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  • CLASSES

    Alpha Adrenoreceptor Antagonists/Alpha Blockers

    DEA CLASS

    Rx

    DESCRIPTION

    Oral alpha-blocker; used primarily for HTN; similar to doxazosin and terazosin, but is shorter-acting; has also been used for CHF, but is seldom used for this indication due to the development of tolerance for drug efficacy.

    COMMON BRAND NAMES

    Minipress

    HOW SUPPLIED

    Minipress/Prazosin/Prazosin Hydrochloride Oral Cap: 1mg, 2mg, 5mg

    DOSAGE & INDICATIONS

    For the treatment of hypertension.
    NOTE: A landmark clinical trial (ALLHAT) compared another alpha-blocker, doxazosin, to chlorthalidone in the treatment of high-risk hypertensive patients. In this study, only the diuretic significantly reduced the risk of combined cardiovascular disease events, especially heart failure. These results led to discontinuation of the alpha-blocker treatment arm of the study.
    Oral dosage
    Adults

    Initially, 1 mg PO given 2 to 3 times per day. The first dose can be given at bedtime to minimize orthostatic hypotension. The average dosage is 6 to 15 mg/day PO, given in divided doses. Maximum dosage is 20 mg/day PO, given in divided doses; however, some patients may need higher doses up to 40 mg/day. When adding additional hypotensive agents or diuretics to prazosin therapy, decrease the dosage of prazosin to 1 to 2 mg PO 3 times per day, then gradually increase as needed.

    Geriatric

    Initially, 1 mg PO given 1 to 2 times per day. Elderly patients may be more sensitive to the hypotensive and adverse effects of prazosin. Adjust dosage based on clinical response.

    Children†

    Initially, 5 mcg/kg PO every 6 hours. Increase dosage gradually to 25 mcg/kg PO every 6 hours. Maximum dosage is 15 mg/day or 400 mcg/kg/day PO. When stable, the total daily dosage can be divided into 2 to 3 doses.

    For the treatment of hypertensive urgency†, especially crises associated with increased circulating catecholamines.
    Oral dosage
    Adults

    Initially, 10 to 20 mg PO. If needed, repeat dose in 30 minutes.

    Geriatric

    See adult dosage. Elderly patients may be more sensitive to the hypotensive and adverse effects of prazosin. Adjust dosage based on clinical response.

    For the prevention of Raynaud's phenomenon†.
    Oral dosage
    Adults

    The dosage range is 0.5 to 3 mg PO twice daily. The first dose can be given at bedtime to minimize orthostatic hypotension. A small study revealed that doses greater than 6 mg/day PO were poorly tolerated. Efficacy may decrease with time.

    Geriatric

    See adult dosage. Elderly patients may be more sensitive to the hypotensive and adverse effects of prazosin. Adjust dosage based on clinical response.

    For the treatment of symptomatic benign prostatic hyperplasia (BPH)†.
    Oral dosage
    Adults

    Initially, 2 mg PO twice daily. The first dose can be given at bedtime to minimize orthostatic hypotension. The maintenance dosage range is 1 to 9 mg/day PO.

    Geriatric

    See adult dosage. Elderly patients may be more sensitive to the hypotensive and adverse effects of prazosin. Adjust dosage based on clinical response.

    For the treatment of posttraumatic stress disorder (PTSD)†, particularly sleep-related disturbances (e.g., nightmares) .
    For the treatment of nightmares† associated with civilian-related PTSD†.
    Oral dosage
    Adults

    Initiate at 1 mg PO once daily at bedtime; may titrate up to 6 mg/day PO at bedtime as needed and tolerated. According to the 2009 American Psychiatric Association (APA) treatment guidelines, prazosin is among the most promising advances in the treatment of post-traumatic stress disorder (PTSD), specifically for treating trauma-related nightmares and sleep disruption. In one study evaluating civilian trauma PTSD (n = 13), patients initially received prazosin 1 mg or placebo PO at bedtime, with titration up to a maximum of 6 mg PO once daily at bedtime. The mean prazosin dose achieved was 3.1 +/- 1.3 mg (range 2 mg/day to 6 mg/day). In the prazosin group, trauma-related nightmares were significantly reduced, total sleep time increased by 94 minutes, and rapid eye movement (REM) sleep time and mean REM period duration increased without an alteration in sleep onset latency. Open-label studies and other published reports also suggest that prazosin is effective in reducing nightmares as well as improving general symptoms of refractory PTSD.

    Adolescents >= 15 years

    According to case reports, doses beginning with 1 mg PO once daily at bedtime and titrated to a range of 1.5 mg/day PO up to 4 mg/day PO once daily at bedtime have resulted in complete resolution of nightmares. Future study through controlled clinical trials is needed to formally assess the safety and efficacy of prazosin in trauma-related sleep disturbances in adolescents.

    For the treatment of combat-related PTSD†, including nightmares†.
    Oral dosage
    Adults

    Gradually titrate from low initial dosages (e.g., 1 mg/day PO at bedtime) up to an effective dose. Usual maximum dose: 15 mg/day PO (given in divided doses at varying time schedules); however, clinical studies did use higher titrations in men. According to the 2009 American Psychiatric Association (APA) treatment guidelines, prazosin is among the most promising advances in the treatment of post-traumatic stress disorder (PTSD), specifically trauma-related nightmares and sleep disruption. Prazosin may be particularly useful in combat-related nightmares since emerging evidence indicates that other widely used medications for PTSD, such as SSRIs, are not as effective in combat-related PTSD symptoms as in non-combat-related PTSD symptoms. In one placebo-controlled trial (n = 40), combat veterans with intractable trauma nightmares and other sleep disturbances were randomized to placebo or an initial prazosin dose of 1 mg PO at bedtime. The prazosin dose could be gradually titrated up to a maximum daily dose of 15 mg/day (5 mg in the morning and 10 mg at bedtime) if clinically indicated. The mean daily prazosin dose was 13 mg/day during the trial. Prazosin demonstrated efficacy in reducing the frequency and intensity of trauma-related nightmares, improving sleep quality, and decreasing overall PTSD symptoms severity. Similar results were observed in a separate trial (n = 10) with prazosin titration up to a maximum of 10 mg/day (6 mg PO at bedtime + 4 mg PO at 3 PM) if clinically indicated (mean total dose 9.5 mg/day). Prazosin was also effective in a third controlled trial evaluating the nightmare item of the Clinician-Administered PTSD Scale (CAPS), the Pittsburgh Sleep Quality Index, and the change item of the Clinical Global Impressions Scale anchored to functioning. The maximum allowed dose was 5 mg midmorning and 20 mg at bedtime for men and 2 mg midmorning and 10 mg at bedtime for women. Lower maximum morning and bedtime doses for women were chosen due to prior clinical observation of the investigators of an apparent increased sensitivity to both beneficial and adverse effects of prazosin in women with PTSD. At study end, the mean prazosin maintenance dose was 4 mg PO in the morning and 15.6 mg PO at bedtime for men, and 1.7 mg PO in the morning and 7 mg PO at bedtime for women. A subgroup analysis of patients randomized to receive prazosin who were established on SSRI therapy revealed a significant reduction in the treatment effect of prazosin in patients who were also receiving an SSRI for CAPS-dream scores, PSQI, and the total CAPS scores. Since a comparison was not made between prazosin patients on SSRIs and placebo patients on SSRIs, it cannot be determined whether this is a result of selection bias for treatment-resistant PTSD sufferers with severe PTSD required for study inclusion, or whether this represents evidence of an antagonistic effect of SSRI treatment on the clinical benefits of prazosin.

    †Indicates off-label use

    MAXIMUM DOSAGE

    Adults

    20 mg/day PO for heart failure or hypertension (some patients have required up to 40 mg/day PO for hypertension); 9 mg/day PO for benign prostatic hyperplasia (BPH).

    Elderly

    20 mg/day PO for heart failure or hypertension (some patients have required up to 40 mg/day PO for hypertension); 9 mg/day PO for benign prostatic hyperplasia (BPH).

    Adolescents

    No maximum dosage information is available. See adult and children's dosage.

    Children

    15 mg/day PO or 400 mcg/kg/day PO.

    DOSING CONSIDERATIONS

    Hepatic Impairment

    No specific recommendations are available for hepatic disease. Since prazosin is extensively metabolized, it is prudent to start with the lowest initial dosage (1 mg PO once daily at bedtime). Monitor and adjust dosage based on clinical response.

    Renal Impairment

    No dosage adjustment is needed.
     
    Intermittent hemodialysis
    No dosage adjustment is needed; prazosin is highly protein bound and is not significantly removed during hemodialysis.

    ADMINISTRATION

    Oral Administration

    Food delays the rate but not the extent of absorption of prazosin.

    STORAGE

    Minipress:
    - Protect from light
    - Protect from moisture
    - Store at controlled room temperature (between 68 and 77 degrees F)

    CONTRAINDICATIONS / PRECAUTIONS

    Angina, hypotension, orthostatic hypotension, syncope

    The addition of prazosin to other antihypertensive agents can cause a rapid decrease in blood pressure. Prazosin should be used with caution in patients with angina pectoris because severe hypotension may cause or worsen angina. Prazosin can cause orthostatic hypotension and syncope, which can be hazardous for patients in certain occupations for which alertness is required. This effect can be dramatic after the initial dose (also known as the "first-dose effect").

    Pregnancy

    Prazosin is classified in FDA pregnancy risk category C. No adequate well-controlled studies in pregnant women have been done to assess the safety of prazosin use during pregnancy. Prazosin should be used in pregnancy only if the benefits to the mother outweigh the risks to the fetus.

    Breast-feeding

    Caution is advisable for breast-feeding mothers because prazosin distributes into breast milk. An alternative agent may be preferred for treating the patient's condition during lactation. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, healthcare providers are encouraged to report the adverse effect to the FDA.

    Ocular surgery

    Patients receiving or who have previously received treatment with alpha-1 blockers, such as prazosin, may be at risk for intraoperative floppy iris syndrome during surgery for cataracts (ocular surgery). Intraoperative floppy iris syndrome is a small pupil syndrome variant that is characterized by a flaccid iris that billows in response to intraoperative irrigation currents, progressive intraoperative miosis despite preoperative dilation with standard mydriatic drugs, and potential prolapse of the iris toward the phacoemulsification incisions. There does not appear to be a benefit of stopping alpha-1 blocker therapy prior to cataract surgery, but ophthalmologists should be prepared for possible modifications to their surgical technique such as the use of iris hooks, iris dilator rings, or viscoelastic substances.

    Priapism

    Prazosin, like other alpha adrenergic antagonists, has been associated with priapism (persistent painful penile erection unrelated to sexual activity). Priapism, if not treated promptly, can result in irreversible damage to the erectile tissue. Males who have an erection lasting greater than 4 hours, whether painful or not, should seek emergency medical attention.

    Geriatric

    Geriatric patients are more likely to be affected by postural hypotension and the possibility of syncope when administered prazosin. Orthostasis may occur frequently in this population, particularly with the first dose of the drug. According to the Beers Criteria, prazosin is considered a potentially inappropriate medication (PIM) in geriatric patients and is not recommended as routine treatment of hypertension due to the high risk of orthostatic hypotension and the availability of alternative agents with a superior benefit to risk profile in the elderly. The Beers panel also recommends avoiding prazosin in geriatric patients whose syncope may be due to orthostasis. Also, avoid use in geriatric females with urinary incontinence of any type because the aggravation of incontinence may occur.[63923] The federal Omnibus Budget Reconciliation Act (OBRA) regulates medication use in residents of long-term care facilities (LTCFs); antihypertensive regimens should be individualized to achieve the desired outcome while minimizing adverse effects. Alpha-blockers may cause dizziness, postural hypotension, fatigue, and there is an increased risk for falls. Prazosin can cause significant hypotension and syncope during the first few doses; therefore, the dose should be administered at bedtime initially, and the drug slowly titrated as needed. Alpha-blockers may require a gradual taper to avoid adverse consequences caused by abrupt discontinuation. Alpha-blockers are infrequently used as a treatment for urinary incontinence; these drugs have specific and limited uses for incontinence and are not approved for this indication. Patients should be assessed periodically for medication effects on urinary incontinence as well as lower urinary tract symptoms and treatment tolerability.[60742]

    ADVERSE REACTIONS

    Severe

    pancreatitis / Delayed / 0-1.0
    bradycardia / Rapid / Incidence not known
    vasculitis / Delayed / Incidence not known

    Moderate

    palpitations / Early / 5.3-5.3
    depression / Delayed / 1.0-4.0
    edema / Delayed / 1.0-4.0
    peripheral edema / Delayed / 1.0-4.0
    dyspnea / Early / 1.0-4.0
    orthostatic hypotension / Delayed / 1.0-4.0
    constipation / Delayed / 1.0-4.0
    blurred vision / Early / 1.0-4.0
    hyperemia / Delayed / 1.0-4.0
    hallucinations / Early / 0-1.0
    sinus tachycardia / Rapid / 0-1.0
    elevated hepatic enzymes / Delayed / 0-1.0
    priapism / Early / 0-1.0
    urinary incontinence / Early / 0-1.0
    impotence (erectile dysfunction) / Delayed / 0-1.0
    hypotension / Rapid / Incidence not known
    angina / Early / Incidence not known
    floppy iris syndrome / Delayed / Incidence not known

    Mild

    dizziness / Early / 10.3-10.3
    headache / Early / 7.8-7.8
    drowsiness / Early / 7.6-7.6
    fatigue / Early / 6.9-6.9
    weakness / Early / 6.5-6.5
    nausea / Early / 4.9-4.9
    anxiety / Delayed / 1.0-4.0
    vertigo / Early / 1.0-4.0
    syncope / Early / 1.0-4.0
    abdominal pain / Early / 1.0-4.0
    vomiting / Early / 1.0-4.0
    xerostomia / Early / 1.0-4.0
    diarrhea / Early / 1.0-4.0
    rash / Early / 1.0-4.0
    increased urinary frequency / Early / 1.0-4.0
    nasal congestion / Early / 1.0-4.0
    epistaxis / Delayed / 1.0-4.0
    paresthesias / Delayed / 0-1.0
    fever / Early / 0-1.0
    arthralgia / Delayed / 0-1.0
    diaphoresis / Early / 0-1.0
    alopecia / Delayed / 0-1.0
    pruritus / Rapid / 0-1.0
    lichen planus-like eruption / Delayed / 0-1.0
    tinnitus / Delayed / 0-1.0
    insomnia / Early / Incidence not known
    asthenia / Delayed / Incidence not known
    gynecomastia / Delayed / Incidence not known
    malaise / Early / Incidence not known
    flushing / Rapid / Incidence not known
    urticaria / Rapid / Incidence not known
    ocular pain / Early / Incidence not known

    DRUG INTERACTIONS

    Acetaminophen; Chlorpheniramine; Dextromethorphan; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Acetaminophen; Chlorpheniramine; Dextromethorphan; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Acetaminophen; Chlorpheniramine; Phenylephrine; Phenyltoloxamine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Acetaminophen; Dextromethorphan; Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Acetaminophen; Dextromethorphan; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Acetaminophen; Dextromethorphan; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Acetaminophen; Dichloralphenazone; Isometheptene: (Major) Sympathomimetics can antagonize the antihypertensive effects of adrenergic agonists when administered concomitantly. Patients should be monitored for loss of blood pressure control.
    Acetaminophen; Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Acetaminophen; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Acrivastine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Aldesleukin, IL-2: (Moderate) Prazosin may potentiate the hypotension seen with aldesleukin, IL-2.
    Alemtuzumab: (Moderate) Alemtuzumab may cause hypotension. Careful monitoring of blood pressure and hypotensive symptoms is recommended especially in patients with ischemic heart disease and in patients on antihypertensive agents.
    Alfuzosin: (Major) Alfuzosin should not be administered in combination with other alpha-blockers. The pharmacokinetic and pharmacodynamic interactions between alfuzosin and other alpha-blockers (used for high blood pressure or for benign prostatic hyperplasia) have not been determined. However, interactions or side effects (dizziness, hypotension, syncope, etc.) may be expected from the duplication of pharmacologic effects.
    Aliskiren: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Aliskiren; Amlodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Aliskiren; Amlodipine; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Aliskiren; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Aliskiren; Valsartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Alprostadil: (Minor) The concomitant use of systemic alprostadil injection and antihypertensive agents, such as prazosin, may cause additive hypotension. Caution is advised with this combination. Systemic drug interactions with the urethral suppository (MUSE) or alprostadil intracavernous injection are unlikely in most patients because low or undetectable amounts of the drug are found in the peripheral venous circulation following administration. In those men with significant corpora cavernosa venous leakage, hypotension might be more likely. Use caution with in-clinic dosing for erectile dysfunction (ED) and monitor for the effects on blood pressure. In addition, the presence of medications in the circulation that attenuate erectile function may influence the response to alprostadil. However, in clinical trials with alprostadil intracavernous injection, anti-hypertensive agents had no apparent effect on the safety and efficacy of alprostadil.
    Ambrisentan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving other antihypertensive agents. Lower dosages of each agent should be used.
    Amifostine: (Major) Patients receiving alpha-blockers should be closely monitored during amifostine infusions due to additive effects. Patients receiving amifostine at doses recommended for chemotherapy should have antihypertensive therapy interrupted 24 hours preceding administration of amifostine. If the antihypertensive cannot be stopped, patients should not receive amifostine.
    Amlodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Amlodipine; Atorvastatin: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Amlodipine; Benazepril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Amlodipine; Hydrochlorothiazide, HCTZ; Olmesartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Amlodipine; Hydrochlorothiazide, HCTZ; Valsartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Amlodipine; Olmesartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Amlodipine; Telmisartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Amlodipine; Valsartan: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin. (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Amobarbital: (Moderate) Concurrent use of amobarbital with antihypertensive agents may lead to hypotension. Monitor for decreases in blood pressure during times of coadministration.
    Amphetamines: (Minor) Close monitoring of blood pressure or the selection of alternative therapeutic agents may be needed in patients receiving prazosin and amphetamines. Amphetamines increase both systolic and diastolic blood pressure and may counteract the activity of some antihypertensive agents, such as prazosin.
    Amyl Nitrite: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary.
    Angiotensin II receptor antagonists: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Angiotensin-converting enzyme inhibitors: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Apomorphine: (Moderate) Use of prazosin and apomorphine together can increase the hypotensive effects of apomorphine. Monitor blood pressure regularly during use of this combination.
    Apraclonidine: (Minor) Alpha blockers as a class may reduce heart rate and blood pressure. While no specific drug interactions have been identified with systemic agents and apraclonidine during clinical trials, it is theoretically possible that additive blood pressure reductions could occur when apraclonidine is combined with the use of antihypertensive agents. Patients using cardiovascular drugs concomitantly with apraclonidine should have their pulse and blood pressure monitored periodically.
    Aripiprazole: (Minor) Aripiprazole may enhance the hypotensive effects of antihypertensive agents.
    Articaine; Epinephrine: (Major) Sympathomimetics, such as epinephrine, can antagonize the effects of alpha-blockers when administered concomitantly. Patients receiving alpha-blockers can exhibit a decreased pressor response to epinephrine, resulting in an increased risk of developing hypotension and tachycardia. Blood pressure should be monitored closely.
    Asenapine: (Moderate) Secondary to alpha-blockade, asenapine can produce vasodilation that may result in additive effects during concurrent use of antihypertensive agents. The potential reduction in blood pressure can precipitate orthostatic hypotension and associated dizziness, tachycardia, and syncope. If concurrent use of asenapine and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
    Avanafil: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on alpha-blocker therapy before initiating therapy with the lowest dose of avanafil. Conversely, patients already receiving an optimized dose of avanafil should be started on the lowest dose of the alpha-blocker; increases in the alpha-blocker dose should be done in a stepwise fashion. Other variables, such as intravascular volume depletion, concurrent antihypertensive therapy, or evidence of hemodynamic instability with alpha-blocker monotherapy, may affect the safety of concomitant use of avanafil and alpha-blockers.
    Azilsartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Azilsartan; Chlorthalidone: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Baclofen: (Moderate) Baclofen has been associated with hypotension. Concurrent use with baclofen and antihypertensive agents may result in additive hypotension. Dosage adjustments of the antihypertensive medication may be required.
    Benazepril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Benazepril; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Beta-blockers: (Moderate) Orthostatic hypotension may be more likely if beta-blockers are coadministered with alpha-blockers.
    Bortezomib: (Moderate) Patients on antihypertensive agents receiving bortezomib treatment may require close monitoring of their blood pressure and dosage adjustment of their medication. During clinical trials of bortezomib, hypotension was reported in roughly 12 percent of patients.
    Bosentan: (Moderate) Although no specific interactions have been documented, bosentan has vasodilatory effects and may contribute additive hypotensive effects when given with antihypertensive alpha-blockers (i.e., doxazosin, phenoxybenzamine, phentolamine, prazosin, terazosin, and tolazoline).
    Brexpiprazole: (Moderate) Due to brexpiprazole's antagonism at alpha 1-adrenergic receptors, the drug may enhance the hypotensive effects of alpha-blockers and other antihypertensive agents.
    Brompheniramine; Carbetapentane; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Brompheniramine; Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Brompheniramine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Cabergoline: (Minor) Cabergoline has minimal affinity for adrenergic receptors; however, it has been associated with hypotension in some instances. Cabergoline should be used cautiously in those receiving antihypertensive agents or other medications known to cause hypotension.
    Calcium-channel blockers: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Candesartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Candesartan; Hydrochlorothiazide, HCTZ: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Captopril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Captopril; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Carbetapentane; Chlorpheniramine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbetapentane; Diphenhydramine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbetapentane; Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbetapentane; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbetapentane; Phenylephrine; Pyrilamine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbetapentane; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Carbidopa; Levodopa: (Moderate) Concomitant use of antihypertensive agents with levodopa can result in additive hypotensive effects.
    Carbidopa; Levodopa; Entacapone: (Moderate) Concomitant use of antihypertensive agents with levodopa can result in additive hypotensive effects.
    Carbinoxamine; Dextromethorphan; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Carbinoxamine; Hydrocodone; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbinoxamine; Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Carbinoxamine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Carbinoxamine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Cariprazine: (Moderate) Orthostatic vital signs should be monitored in patients who are at risk for hypotension, such as those receiving cariprazine in combination with antihypertensive agents. Atypical antipsychotics may cause orthostatic hypotension and syncope, most commonly during treatment initiation and dosage increases. Patients should be informed about measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning, or rising slowly from a seated position. Consider a cariprazine dose reduction if hypotension occurs.
    Central-acting adrenergic agents: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Cetirizine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlophedianol; Dexchlorpheniramine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlophedianol; Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Chlorpheniramine; Dextromethorphan; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Chlorpheniramine; Dihydrocodeine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Chlorpheniramine; Dihydrocodeine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlorpheniramine; Guaifenesin; Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlorpheniramine; Hydrocodone; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Chlorpheniramine; Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlorpheniramine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Chlorpheniramine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Chlorthalidone; Clonidine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Clevidipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Clonidine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Clozapine: (Moderate) Clozapine used concomitantly with the antihypertensive agents can increase the risk and severity of hypotension by potentiating the effect of the antihypertensive drug.
    Codeine; Phenylephrine; Promethazine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Co-Enzyme Q10, Ubiquinone: (Moderate) Co-enzyme Q10, ubiquinone (CoQ10) may lower blood pressure. CoQ10 use in combination with antihypertensive agents may lead to additional reductions in blood pressure in some individuals. Patients who choose to take CoQ10 concurrently with antihypertensive medications should receive periodic blood pressure monitoring. Patients should be advised to inform their prescriber of their use of CoQ10.
    Darolutamide: (Moderate) Caution is advised with the coadministration of darolutamide and prazosin due to the potential for increased plasma concentrations of prazosin increasing the risk of adverse effects. Prazosin is a substrate of breast cancer resistance protein (BCRP) and darolutamide is a BCRP inhibitor.
    Desloratadine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Dexchlorpheniramine; Dextromethorphan; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Dexmethylphenidate: (Moderate) Dexmethylphenidate can reduce the hypotensive effect of antihypertensive agents, including alpha-blockers. Periodic evaluation of blood pressure is advisable during concurrent use of dexmethylphenidate and antihypertensive agents, particularly during initial coadministration and after dosage increases of dexmethylphenidate.
    Dextromethorphan; Diphenhydramine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Dextromethorphan; Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Dextromethorphan; Guaifenesin; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Dextromethorphan; Quinidine: (Moderate) Quinidine can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents due to the potential for additive hypotension.
    Diazoxide: (Moderate) Additive hypotensive effects can occur with the concomitant administration of diazoxide with other antihypertensive agents. This interaction can be therapeutically advantageous, but dosages must be adjusted accordingly. The manufacturer advises that IV diazoxide should not be administered to patients within 6 hours of receiving other antihypertensive agents.
    Diethylpropion: (Major) Diethylpropion has vasopressor effects and may limit the benefit of alpha-blockers. Although leading drug interaction texts differ in the potential for an interaction between diethylpropion and this group of antihypertensive agents, these effects are likely to be clinically significant and have been described in hypertensive patients on these medications.
    Dihydrocodeine; Guaifenesin; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Diltiazem: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Diphenhydramine; Hydrocodone; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Diphenhydramine; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Dobutamine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Dopamine: (Major) In general, alpha-blockers should not be used during dopamine infusion. The undesired peripheral vasoconstriction observed with high-dose dopamine is opposed by alpha-adrenergic blockers. The renal, mesenteric, or cerebral vasodilatory properties resulting from dopaminergic-receptor stimulation are not affected by alpha-blockers .
    Drospirenone; Ethinyl Estradiol: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Drospirenone; Ethinyl Estradiol; Levomefolate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Duloxetine: (Moderate) Orthostatic hypotension and syncope have been reported during duloxetine administration. The concurrent administration of antihypertensive agents and duloxetine may increase the risk of hypotension. Monitor blood pressure if the combination is necessary.
    Dutasteride; Tamsulosin: (Major) Tamsulosin should not be administered in combination with other alpha-blockers. The pharmacokinetic and pharmacodynamic interactions between tamsulosin and other alpha-blockers (used for high blood pressure or for benign prostatic hyperplasia) have not been determined. However, interactions or side effects (dizziness, hypotension, syncope, etc.) may be expected from the duplication of pharmacologic effects.
    Enalapril, Enalaprilat: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Enalapril; Felodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Enalapril; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Enflurane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Ephedrine: (Major) The cardiovascular effects of sympathomimetics, such as ephedrine, may reduce the antihypertensive effects produced by alpha-blockers. Blood pressure and heart rates should be monitored closely to confirm that the desired antihypertensive effect is achieved.
    Epinephrine: (Major) Sympathomimetics, such as epinephrine, can antagonize the effects of alpha-blockers when administered concomitantly. Patients receiving alpha-blockers can exhibit a decreased pressor response to epinephrine, resulting in an increased risk of developing hypotension and tachycardia. Blood pressure should be monitored closely.
    Eplerenone: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Epoprostenol: (Minor) Epoprostenol can have additive effects when administered with other antihypertensive agents, including alpha-blockers. These effects can be used to therapeutic advantage, but dosage adjustments may be necessary.
    Eprosartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Eprosartan; Hydrochlorothiazide, HCTZ: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Estradiol Cypionate; Medroxyprogesterone: (Minor) Estrogens can induce fluid retention and may increase blood pressure in some patients; patients who are receiving antihypertensive agents concurrently with hormonal contraceptives should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Estradiol: (Minor) Estrogens can induce fluid retention and may increase blood pressure in some patients; patients who are receiving antihypertensive agents concurrently with hormonal contraceptives should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethanol: (Moderate) Some experts and manufacturers advise that the patient to limit alcohol use while using alpha-blockers. Alcohol-containing beverages may increase the effects of alpha-blockers, which may lower the blood pressure.
    Ethinyl Estradiol: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Desogestrel: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Ethynodiol Diacetate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Etonogestrel: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Levonorgestrel: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Levonorgestrel; Ferrous bisglycinate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Levonorgestrel; Folic Acid; Levomefolate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norelgestromin: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norethindrone Acetate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norethindrone Acetate; Ferrous fumarate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norethindrone: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norethindrone; Ferrous fumarate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norgestimate: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Ethinyl Estradiol; Norgestrel: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Etomidate: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Felodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Fenoldopam: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Fexofenadine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Fish Oil, Omega-3 Fatty Acids (Dietary Supplements): (Moderate) High doses of fish oil supplements may produce a blood pressure lowering effect. It is possible that additive reductions in blood pressure may be seen when fish oils are used in a patient already taking antihypertensive agents.
    Fosinopril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Fosinopril; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Fospropofol: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    General anesthetics: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Guaifenesin; Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Guaifenesin; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Guaifenesin; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Guanabenz: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Guanfacine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Haloperidol: (Moderate) In general, haloperidol should be used cautiously with antihypertensive agents due to the possibility of additive hypotension.
    Halothane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Hydralazine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydralazine; Hydrochlorothiazide, HCTZ: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydralazine; Isosorbide Dinitrate, ISDN: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Irbesartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Lisinopril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Losartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Methyldopa: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Moexipril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Olmesartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Quinapril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Telmisartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrochlorothiazide, HCTZ; Valsartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Hydrocodone; Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Hydrocodone; Potassium Guaiacolsulfonate; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Hydrocodone; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Ibuprofen; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Iloperidone: (Moderate) Secondary to alpha-blockade, iloperidone can produce vasodilation that may result in additive effects during concurrent use with antihypertensive agents. The potential reduction in blood pressure can precipitate orthostatic hypotension and associated dizziness, tachycardia, and syncope. If concurrent use of iloperidone and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
    Iloprost: (Moderate) Further reductions in blood pressure may occur when inhaled iloprost is administered to patients receiving other antihypertensive agents.
    Indapamide: (Moderate) The effects of indapamide may be additive when administered with other antihypertensive agents or diuretics. This may be desirable, but occasionally orthostatic hypotension may occur. Decreased indapamide dosages may be necessary during concomitant use.
    Intravenous Lipid Emulsions: (Moderate) High doses of fish oil supplements may produce a blood pressure lowering effect. It is possible that additive reductions in blood pressure may be seen when fish oils are used in a patient already taking antihypertensive agents.
    Irbesartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Isocarboxazid: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with antihypertensives. Careful monitoring of blood pressure is suggested during concurrent therapy with antihypertensives such as alpha-blockers. Patients should be instructed to rise slowly from a sitting position, and to report syncope or changes in blood pressure or heart rate to their health care provider.
    Isoflurane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Isoproterenol: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Isosorbide Dinitrate, ISDN: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary.
    Isosorbide Mononitrate: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary.
    Isradipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Ketamine: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Levodopa: (Moderate) Concomitant use of antihypertensive agents with levodopa can result in additive hypotensive effects.
    Lisinopril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Lofexidine: (Major) Because the central alpha-2 agonist effects of lofexidine can cause hypotension and orthostasis, the drug should be avoided, if possible, in combination with other medications that can significantly decrease blood pressure such as the antihypertensive alpha-blockers. If coadministration is required, blood pressure should be monitored, particularly after dose changes of either agent. Adjustments should be made as clinically indicated. Patients being given lofexidine in an outpatient setting should be capable of and instructed on self-monitoring for hypotension, orthostasis, bradycardia, and associated symptoms. If clinically significant or symptomatic hypotension and/or bradycardia occur, the next dose of lofexidine should be reduced in amount, delayed, or skipped.
    Loop diuretics: (Moderate) The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving loop diuretics. This effect can be minimized by reducing the prazosin dose to 1 to 2 mg three times a day, by introducing the loop diuretic cautiously, and then by retitrating prazosin to clinical response.
    Loratadine; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Losartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Lovastatin; Niacin: (Moderate) Cutaneous vasodilation induced by niacin may become problematic if high-dose niacin is used concomitantly with other antihypertensive agents. This effect is of particular concern in the setting of acute myocardial infarction, unstable angina, or other acute hemodynamic compromise.
    Lurasidone: (Moderate) Due to the antagonism of lurasidone at alpha-1 adrenergic receptors, the drug may enhance the hypotensive effects of alpha-blockers and other antihypertensive agents. If concurrent use of lurasidone and antihypertensive agents is necessary, patients should be counseled on measures to prevent orthostatic hypotension, such as sitting on the edge of the bed for several minutes prior to standing in the morning and rising slowly from a seated position. Close monitoring of blood pressure is recommended until the full effects of the combination therapy are known.
    Mestranol; Norethindrone: (Minor) Estrogen containing oral contraceptives can induce fluid retention and may increase blood pressure in some patients; monitor patients receiving concurrent therapy to confirm that the desired antihypertensive effect is being obtained.
    Methohexital: (Moderate) Concurrent use of methohexital and alpha-blockers increases the risk of developing hypotension and hypothermia.
    Methyldopa: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Methylphenidate: (Minor) Periodic evaluation of blood pressure is advisable during concurrent use of methylphenidate and antihypertensive agents, particularly during initial coadministration and after dosage increases of methylphenidate. Methylphenidate can reduce the hypotensive effect of antihypertensive agents such as alpha-blockers.
    Midodrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Milrinone: (Moderate) Concurrent administration of antihypertensive agents could lead to additive hypotension when administered with milrinone. Titrate milrinone dosage according to hemodynamic response.
    Minoxidil: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Moexipril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Naproxen; Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Nebivolol; Valsartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Nesiritide, BNP: (Major) The potential for hypotension may be increased when coadministering nesiritide with antihypertensive agents.
    Niacin, Niacinamide: (Moderate) Cutaneous vasodilation induced by niacin may become problematic if high-dose niacin is used concomitantly with other antihypertensive agents. This effect is of particular concern in the setting of acute myocardial infarction, unstable angina, or other acute hemodynamic compromise.
    Niacin; Simvastatin: (Moderate) Cutaneous vasodilation induced by niacin may become problematic if high-dose niacin is used concomitantly with other antihypertensive agents. This effect is of particular concern in the setting of acute myocardial infarction, unstable angina, or other acute hemodynamic compromise.
    Nicardipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Nicotine: (Moderate) Nicotine use may reduce the clinical effects of the alpha-blockers. If significant changes in nicotine intake occur, the dosages of these drugs may need adjustment.
    Nifedipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Nimodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Nisoldipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Nitrates: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary.
    Nitroglycerin: (Moderate) Concomitant use of nitrates with other antihypertensive agents can cause additive hypotensive effects. Dosage adjustments may be necessary.
    Nitroprusside: (Moderate) Additive hypotensive effects may occur when nitroprusside is used concomitantly with other antihypertensive agents. Dosages should be adjusted carefully, according to blood pressure.
    Nonsteroidal antiinflammatory drugs: (Moderate) If nonsteroidal anti-inflammatory drugs (NSAIDs) and an antihypertensive drug are concurrently used, carefully monitor the patient for signs and symptoms of renal insufficiency and blood pressure control. Doses of antihypertensive medications may require adjustment in patients receiving concurrent NSAIDs. NSAIDs, to varying degrees, have been associated with an elevation in blood pressure. This effect is most significant in patients receiving concurrent antihypertensive agents and long-term NSAID therapy. NSAIDs cause a dose-dependent reduction in prostaglandin formation, which may result in a reduction in renal blood flow leading to renal insufficiency and an increase in blood pressure that are often accompanied by peripheral edema and weight gain. Patients who rely upon renal prostaglandins to maintain renal perfusion may have acute renal blood flow reduction with NSAID usage. Elderly patients may be at increased risk of adverse effects from combined long-term NSAID therapy and antihypertensive agents, especially diuretics, due to age-related decreases in renal function and an increased risk of stroke and coronary artery disease.
    Norepinephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly. Also, because norepinephrine is an alpha-adrenergic agonist, drugs with alpha-blocking activity such as alpha-blockers directly counteract the vasopressor effects of norepinephrine.
    Olmesartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Oxymetazoline: (Major) Caution is advised when administering prazosin with oxymetazoline. Prazosin, an alpha adrenergic blocker, would likely antagonize the sympathomimetic effects of oxymetazoline, alpha adrenergic agonists; thereby reducing the effectiveness of oxymetazoline.
    Paliperidone: (Moderate) Paliperidone may cause orthostatic hypotension, thereby enhancing the hypotensive effects of antihypertensive agents. Orthostatic vital signs should be monitored in patients receiving paliperidone and prazosin who are susceptible to hypotension.
    Pentoxifylline: (Moderate) Pentoxifylline has been used concurrently with antihypertensive drugs (beta blockers, diuretics) without observed problems. Small decreases in blood pressure have been observed in some patients treated with pentoxifylline; periodic systemic blood pressure monitoring is recommended for patients receiving concomitant antihypertensives. If indicated, dosage of the antihypertensive agents should be reduced.
    Perindopril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Perindopril; Amlodipine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Phendimetrazine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Phenelzine: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with antihypertensives. Careful monitoring of blood pressure is suggested during concurrent therapy with antihypertensives such as alpha-blockers. Patients should be instructed to rise slowly from a sitting position, and to report syncope or changes in blood pressure or heart rate to their health care provider.
    Phentermine: (Moderate) Monitor for desired antihypertensive effect of alpha-blockers when administered with phentermine, Sympathomimetics like phentermine can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Phentermine; Topiramate: (Moderate) Monitor for desired antihypertensive effect of alpha-blockers when administered with phentermine, Sympathomimetics like phentermine can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Phenylephrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Phenylephrine; Promethazine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Potassium-sparing diuretics: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Prilocaine; Epinephrine: (Major) Sympathomimetics, such as epinephrine, can antagonize the effects of alpha-blockers when administered concomitantly. Patients receiving alpha-blockers can exhibit a decreased pressor response to epinephrine, resulting in an increased risk of developing hypotension and tachycardia. Blood pressure should be monitored closely.
    Procainamide: (Moderate) Procainamide can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents. Intravenous administration of procainamide is more likely to cause hypotensive effects.
    Procaine: (Moderate) Local anesthetics may cause additive hypotension in combination with antihypertensive agents.
    Propofol: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Pseudoephedrine: (Moderate) The cardiovascular effects of pseudoephedrine may reduce the antihypertensive effects produced by alpha-blockers. Monitor blood pressure and heart rate.
    Quinapril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Quinidine: (Moderate) Quinidine can decrease blood pressure and should be used cautiously in patients receiving antihypertensive agents due to the potential for additive hypotension.
    Ramipril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Rasagiline: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with antihypertensives. Careful monitoring of blood pressure is suggested during concurrent therapy with antihypertensives such as alpha-blockers. Patients should be instructed to rise slowly from a sitting position, and to report syncope or changes in blood pressure or heart rate to their health care provider.
    Reserpine: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Risperidone: (Moderate) Risperidone may induce orthostatic hypotension and thus enhance the hypotensive effects of antihypertensive agents. Lower initial doses or slower dose titration of risperidone may be necessary in patients receiving antihypertensive agents concomitantly.
    Ritodrine: (Major) Sympathomimetics can antagonize the effects of antihypertensives such as alpha-blockers when administered concomitantly.
    Sacubitril; Valsartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Segesterone Acetate; Ethinyl Estradiol: (Minor) Estrogen-containing oral contraceptive may induce fluid retention and may increase blood pressure in some patients taking antihypertensive agents. Such patients should be monitored to confirm that the desired antihypertensive effect is being obtained.
    Selegiline: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with antihypertensives. Careful monitoring of blood pressure is suggested during concurrent therapy with antihypertensives such as alpha-blockers. Patients should be instructed to rise slowly from a sitting position, and to report syncope or changes in blood pressure or heart rate to their health care provider.
    Sevoflurane: (Moderate) General anesthetics can potentiate the hypotensive effects of antihypertensive agents.
    Sildenafil: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on alpha-blocker therapy before initiating therapy with the lowest dose of sildenafil. Conversely, patients already receiving an optimized dose of sildenafil should be started on the lowest dose of the alpha-blocker; increases in the alpha-blocker dose should be done in a stepwise fashion. Other variables, such as intravascular volume depletion, concurrent antihypertensive therapy, or evidence of hemodynamic instability with alpha-blocker monotherapy, may affect the safety of concomitant use of sildenafil and an alpha-blocker.
    Silodosin: (Major) Silodosin should not be administered in combination with other alpha-blockers. The pharmacokinetic and pharmacodynamic interactions between silodosin and other alpha-blockers (used for high blood pressure or for benign prostatic hyperplasia) have not been determined. However, interactions or side effects (dizziness, hypotension, syncope, etc.) may be expected from the duplication of pharmacologic effects.
    Tadalafil: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on alpha-blocker therapy before initiating therapy with the lowest recommended dose of tadalafil. Conversely, patients already receiving an optimized dose of tadalafil should be started on the lowest dose of the alpha-blocker; increases in the alpha-blocker dose should be done in stepwise fashion. When tadalafil is used for benign prostatic hypertrophy (BPH), discontinue alpha-blocker therapy at least 1 day prior to initiating tadalafil therapy. Other variables, such as intravascular volume depletion, concurrent antihypertensive therapy, or evidence of hemodynamic instability with alpha-blocker monotherapy, may affect the safety of concomitant use of tadalafil and an alpha-blocker.
    Tafamidis: (Moderate) Caution is advised with the coadministration of tafamidis and prazosin due to the potential for increased plasma concentrations of prazosin increasing the risk of adverse effects. Prazosin dose adjustment may be needed with coadministration. Prazosin is a substrate of breast cancer resistance protein (BCRP) and tafamidis is a BCRP inhibitor.
    Tamsulosin: (Major) Tamsulosin should not be administered in combination with other alpha-blockers. The pharmacokinetic and pharmacodynamic interactions between tamsulosin and other alpha-blockers (used for high blood pressure or for benign prostatic hyperplasia) have not been determined. However, interactions or side effects (dizziness, hypotension, syncope, etc.) may be expected from the duplication of pharmacologic effects.
    Telmisartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Tetrabenazine: (Moderate) Tetrabenazine may induce orthostatic hypotension and thus enhance the hypotensive effects of antihypertensive agents. Lower initial doses or slower dose titration of tetrabenazine may be necessary in patients receiving antihypertensive agents concomitantly.
    Tetracaine: (Moderate) Local anesthetics may cause additive hypotension in combination with antihypertensive agents. Use extreme caution with the concomitant use of tetracaine and antihypertensive agents.
    Thalidomide: (Moderate) Thalidomide and other agents that slow cardiac conduction such as alpha-blockers should be used cautiously due to the potential for additive bradycardia.
    Thiazide diuretics: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Thiopental: (Moderate) Concurrent use of thiopental and alpha-blockers or antihypertensive agents increases the risk of developing hypotension.
    Thiothixene: (Moderate) Thiothixene should be used cautiously in patients receiving antihypertensive agents. Additive hypotensive effects are possible.
    Tizanidine: (Moderate) Concurrent use of tizanidine with antihypertensive agents can result in significant hypotension. Caution is advised when tizanidine is to be used in patients receiving concurrent antihypertensive therapy.
    Trandolapril: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Trandolapril; Verapamil: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Tranylcypromine: (Severe) The use of hypotensive agents and tranylcypromine is contraindicated by the manufacturer of tranylcypromine because the effects of hypotensive agents may be markedly potentiated.
    Trazodone: (Minor) Due to additive hypotensive effects, patients receiving antihypertensive agents concurrently with trazodone may have excessive hypotension. Decreased dosage of the antihypertensive agent may be required when given with trazodone.
    Treprostinil: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Valsartan: (Moderate) razosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used.
    Vardenafil: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on alpha-blocker therapy before initiating therapy with the lowest dose of vardenafil. Conversely, patients already receiving an optimized dose of vardenafil should be started on the lowest dose of the alpha-blocker; increases in the alpha-blocker dose should be done in a stepwise fashion. Other variables, such as intravascular volume depletion, concurrent antihypertensive therapy, or evidence of hemodynamic instability with alpha-blocker monotherapy, may affect the safety of concomitant use of vardenafil and an alpha-blocker.
    Verapamil: (Moderate) Prazosin is well-known to produce a 'first-dose' phenomenon. Some patients develop significant hypotension shortly after administration of the first dose. The first dose response (acute postural hypotension) of prazosin may be exaggerated in patients who are receiving beta-adrenergic blockers, diuretics, or other antihypertensive agents. Concomitant administration of prazosin with other antihypertensive agents is not prohibited, however. This can be therapeutically advantageous, but lower dosages of each agent should be used. The use of alpha-blockers with verapamil can lead to excessive hypotension; In addition, verapamil has been reported to increase the AUC and Cmax of prazosin.
    Yohimbine: (Moderate) Yohimbine can increase blood pressure and therefore can antagonize the therapeutic action of antihypertensive agents in general. Use with particular caution in hypertensive patients with high or uncontrolled BP.
    Ziprasidone: (Minor) Ziprasidone is a moderate antagonist of alpha-1 receptors and may cause orthostatic hypotension with or without tachycardia, dizziness, or syncope. Additive hypotensive effects are possible if ziprasidone is used concurrently with antihypertensive agents.

    PREGNANCY AND LACTATION

    Pregnancy

    Prazosin is classified in FDA pregnancy risk category C. No adequate well-controlled studies in pregnant women have been done to assess the safety of prazosin use during pregnancy. Prazosin should be used in pregnancy only if the benefits to the mother outweigh the risks to the fetus.

    Caution is advisable for breast-feeding mothers because prazosin distributes into breast milk. An alternative agent may be preferred for treating the patient's condition during lactation. Consider the benefits of breast-feeding, the risk of potential infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally administered drug, healthcare providers are encouraged to report the adverse effect to the FDA.

    MECHANISM OF ACTION

    Mechanism of Action: Prazosin is a competitive antagonist at postsynaptic alpha1-receptors, unlike phenoxybenzamine and phentolamine, which are nonspecific alpha-receptor antagonists. By sparing presynaptic alpha2-receptors, prazosin does not activate norepinephrine release and, in turn, prazosin has a lower incidence of reflex tachycardia than does either phenoxybenzamine or phentolamine. Prazosin causes peripheral vasodilation by selective, competitive inhibition of vascular postsynaptic alpha1-adrenergic receptors, thus reducing peripheral vascular resistance and blood pressure.Prazosin reduces blood pressure when patients are in either the supine or standing positions, with more dramatic effects on diastolic blood pressure. Since alpha-receptors are predominantly located in the peripheral, superficial circulation, prazosin is effective in the treatment of Raynaud's phenomenon. There is no change in cardiac output or heart rate in these patients, and the response to exercise remains essentially the same. Patients with congestive heart failure who receive prazosin show marked decreases in systemic and pulmonary venous pressures and right atrial pressure, while cardiac output generally increases. In cases of congestive heart failure associated with mitral or aortic valve regurgitation, prazosin may reduce regurgitant volume while increasing cardiac output.In the treatment of benign prostatic hypertrophy (BPH), prazosin relaxes the bladder neck and the prostate by blocking the alpha1-adrenergic receptors located in their smooth muscle. This causes less pressure on the urethra and increases urine flow. Prazosin is effective in treating BPH.Peripheral alpha1-blockers have not been reported to cause serum lipid abnormalities, and therefore may be considered appropriate in hypertensive patients with concurrent hyperlipidemia. Further, these agents have been observed to decrease plasma levels of total cholesterol, LDL, and triglycerides. The clinical implications of these effects are not completely known. Prazosin also does not worsen and may improve LVH, does not worsen insulin resistance, and causes only mild sexual dysfunction.

    PHARMACOKINETICS

    Prazosin is administered orally. Complete antihypertensive effects may not occur for 4—6 weeks. The drug distributes widely throughout the body tissues and is extensively protein-bound (97%). Prazosin is highly metabolized in the liver by demethylation and conjugation, with the majority of an oral dose being eliminated via biliary excretion (in the feces) and the remainder excreted in the urine. Four prazosin metabolites possess 10—15% of the activity of the parent drug and may contribute to prazosin's antihypertensive effects. Antihypertensive effects peak in 2—4 hours. The plasma half-life of prazosin is 2—4 hours, and the duration of antihypertensive effects is less than 24 hours.

    Oral Route

    Prazosin absorption varies following oral administration.