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    1st Generation Cephalosporin Antibiotics

    DEA CLASS

    Rx

    DESCRIPTION

    Oral, first-generation cephalosporin used primarily for otitis media and infections of the respiratory tract due to susceptible staphylococci, Streptococcus pneumoniae, and group A beta-hemolytic streptococci.

    COMMON BRAND NAMES

    Biocef, Daxbia, Keflex

    HOW SUPPLIED

    Biocef/Cephalexin Monohydrate/Daxbia/Keflex Oral Cap: 250mg, 333mg, 500mg, 750mg
    Biocef/Cephalexin Monohydrate/Keflex Oral Pwd F/Recon: 5mL, 125mg, 250mg
    Cephalexin Monohydrate Oral Tab: 250mg, 500mg

    DOSAGE & INDICATIONS

    For the treatment of upper respiratory tract infections, including tonsillitis and/or pharyngitis secondary to Streptococcus pyogenes (i.e., primary rheumatic fever prophylaxis).
    Oral dosage
    Adults

    500 mg PO every 12 hours for 10 days for group A streptococcal pharyngitis as an alternative for those with non-immediate type penicillin allergy per clinical practice guidelines. The FDA-approved dosage is 1 to 4 g daily, divided in 2 to 4 doses and generally 250 mg PO every 6 hours or 500 mg PO every 12 hours; higher doses may be necessary for more severe infections. Maximum dose is 4 g/day. In general, a treatment duration of 7 to 14 days is recommended for most indications.

    Children and Adolescents

    20 mg/kg/dose (Max: 500 mg/dose) PO twice daily for 10 days for group A streptococcal pharyngitis as an alternative for those with non-immediate type penicillin allergy per clinical practice guidelines. The FDA-approved dosage range is 25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day). For severe infections, 50 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 4 g/day) may be used. In general, a treatment duration of 7 to 14 days is recommended for most indications. Cephalexin given twice daily has been shown to achieve comparable bacteriologic and clinical cure rates as cephalexin given 3 or 4 times daily in clinical studies of children with group A beta-hemolytic streptococcal tonsillopharyngitis.

    Infants†

    20 mg/kg/dose PO twice daily for 10 days is recommended for group A streptococcal pharyngitis as an alternative for those with non-immediate type penicillin allergy per clinical practice guidelines.

    For the treatment of lower respiratory tract infections (e.g., pneumonia, community-acquired pneumonia).
    Oral dosage
    Adults

    1 to 4 g daily, divided in 2 to 4 equal doses and generally 250 mg PO every 6 hours or 500 mg PO every 12 hours; higher doses may be necessary for more severe infections. Maximum dose is 4 g/day. In general, a treatment duration of 7 to 14 days is recommended for most indications. Clinical practice guidelines for community-acquired pneumonia (CAP) suggest a first generation cephalosporin may be used for methicillin-sensitive Staphylococcus aureus (MSSA). Patients should be treated for at least 5 days and should be afebrile for 48 to 72 hours with no more than 1 CAP-associated sign of clinical instability before discontinuing therapy. A longer duration may be needed if the initial therapy is not active against identified pathogens or if there are complications.

    Infants†, Children, and Adolescents

    25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day) for mild to moderate infections or 50 to 100 mg/kg/day (Max: 4 g/day) PO in 3 to 4 divided doses for severe infections. For community-acquired pneumonia (CAP) due to methicillin-sensitive Staphylococcus aureus (MSSA) in children 3 months and older, 75 to 100 mg/kg/day PO in 3 or 4 divided doses (Max: 4 g/day) for 10 days is recommended by clinical practice guidelines. Cephalexin is recommended as the preferred oral step-down therapy or initial therapy for mild infection.

    For the treatment skin and skin structure infections (e.g., cellulitis, impetigo) due to susceptible organisms.
    Oral dosage
    Adults

    1 to 4 g daily, divided in 2 to 4 equal doses and generally 250 mg PO every 6 hours or 500 mg PO every 12 hours; higher doses may be necessary for more severe infections. Maximum dose is 4 g/day. In general, a treatment duration of 7 to 14 days is recommended for most indications. Clinical practice guidelines recommend 500 mg PO every 6 hours for methicillin-susceptible Staphylococcus aureus (MSSA) or streptococcal infections and 250 mg PO every 6 hours for 7 days for impetigo or ecthyma. Cephalexin is included as an option for the treatment of mild nonpurulent SSTIs (e.g., cellulitis) and for moderate purulent SSTIs (e.g., furuncle, carbuncle, abscess) caused by MSSA. Unless cultures have yielded streptococci alone, ecthyma or impetigo therapy should cover Staphylococcus aureus. Because S. aureus isolates from ecthyma or impetigo are usually methicillin susceptible, cephalexin is recommended.

    Infants†, Children, and Adolescents

    25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day for most SSTIs, Max: 1 g/day for impetigo). In general, a treatment duration of 7 to 14 days is recommended for most indications. Cephalexin is included as an option for the treatment of mild nonpurulent SSTIs (e.g., cellulitis) and for moderate purulent SSTIs (e.g., furuncle, carbuncle, abscess) caused by MSSA. Unless cultures have yielded streptococci alone, ecthyma or impetigo therapy should cover Staphylococcus aureus. Because S. aureus isolates from ecthyma or impetigo are usually methicillin susceptible, cephalexin is recommended; treat for 7 days.

    For the treatment of otitis media.
    Oral dosage
    Infants†, Children, and Adolescents

    75 to 100 mg/kg/day PO given in 3 to 4 divided doses (Max: 2 to 4 g/day). Although cephalexin is FDA-approved for the treatment of otitis media, it is not recommended as a treatment option in clinical practice guidelines. Second- or third-generation oral cephalosporins (i.e., cefdinir, cefuroxime, and cefpodoxime) are the recommended agents for patients allergic to amoxicillin.

    For the treatment of bone and joint infections (i.e., osteomyelitis, infectious arthritis).
    Oral dosage
    Adults

    1 to 4 g daily, divided in 2 to 4 doses and generally 250 mg PO every 6 hours or 500 mg PO every 12 hours; higher doses may be necessary for more severe infections. Maximum dose is 4 g/day. In general, a treatment duration of 7 to 14 days is recommended for most indications. Clinical practice guidelines suggest 500 mg PO 3 to 4 times daily as an alternative to a fluoroquinolone for prosthetic joint infections in combination with rifampin after initial IV treatment. Treat for 3 to 6 months depending on the infected joint. Depending on organism, cephalexin is also recommended as a preferred or alternate treatment for chronic suppression.

    Infants†, Children, and Adolescents

    100 mg/kg/day PO in 4 divided doses is commonly used in clinical practice and is recommended in clinical practice guidelines for septic arthritis. The FDA-approved dosage for severe infections in pediatric patients older than 1 year is 50 to 100 mg/kg/day PO in 3 to 4 divided doses (Max: 4 g/day).

    For the treatment of genitourinary infection (i.e., urinary tract infection (UTI), cystitis, prostatitis).
    Oral dosage
    Adults

    1 to 4 g daily, divided in 2 to 4 doses and generally 250 mg PO every 6 hours or 500 mg PO every 12 hours; higher doses may be necessary for more severe infections. Maximum dose is 4 g/day. In general, a treatment duration of 7 to 14 days is recommended for most indications. Clinical practice guidelines recommend a beta-lactam for 3 to 7 days as alternative therapy for cystitis when other agents cannot be used. Beta-lactams generally have inferior efficacy than other agents.

    Children and Adolescents 3 years and older

    25 to 50 mg/kg/day PO in 2 to 4 divided doses (Max: 2 g/day). For severe infections, 50 to 100 mg/kg/day PO PO in 3 to 4 divided doses (Max: 4 g/day) may be used. In general, a treatment duration of 7 to 14 days is recommended for most indications.

    Infants† and Children 2 months to 2 years

    50 to 100 mg/kg/day PO in 4 divided doses for 7 to 14 days is recommended by the American Academy of Pediatrics (AAP) for the treatment of initial UTI in febrile infants and young children. The general FDA-approved dosage for pediatric patients older than 1 year is 25 to 50 mg/kg/day PO in 2 to 4 divided doses. For severe infections, 50 to 100 mg/kg/day PO in 3 to 4 divided doses may be used. In general, a treatment duration of 7 to 14 days is recommended for most indications.

    For bacterial endocarditis prophylaxis†.
    Oral dosage
    Adults

    2 g PO as a single dose given 30 to 60 minutes before procedure as an alternative for patients allergic to penicillin. Prophylaxis is recommended for at-risk cardiac patients who are undergoing dental procedures that involve manipulation of gingival tissue, manipulation of the periapical region of teeth, or perforation of the oral mucosa. Cardiac patients that are considered to be at highest risk include those with prosthetic cardiac valves or prosthetic material used for cardiac valve repair, previous infective endocarditis, select types of congenital heart disease (CHD), and cardiac transplantation with valvulopathy.

    Children and Adolescents

    50 mg/kg PO as a single dose (Max: 2 g/dose) given 30 to 60 minutes before procedure as an alternative for patients allergic to penicillin. Prophylaxis is recommended for at-risk cardiac patients who are undergoing dental procedures that involve manipulation of gingival tissue, manipulation of the periapical region of teeth, or perforation of the oral mucosa. Cardiac patients that are considered to be at highest risk include those with prosthetic cardiac valves or prosthetic material used for cardiac valve repair, previous infective endocarditis, select types of congenital heart disease (CHD), and cardiac transplantation with valvulopathy.

    †Indicates off-label use

    MAXIMUM DOSAGE

    Adults

    4 grams/day PO.

    Geriatric

    4 grams/day PO.

    Adolescents

    100 mg/kg/day PO (Max: 4 grams/day).

    Children

    100 mg/kg/day PO (Max: 4 grams/day).

    Infants

    100 mg/kg/day PO.

    Neonates

    Safety and efficacy have not been established; however, doses up to 15 mg/kg/day PO have been used for UTI prophylaxis.

    DOSING CONSIDERATIONS

    Hepatic Impairment

    No dosage adjustment is necessary.

    Renal Impairment

    FDA-approved dosage adjustments (adults and adolescents at least 15 years of age)
    CrCl 60 mL/minute or greater: No dosage adjustment is needed.
    CrCl 30 to 59 mL/minute: No dosage adjustment is needed; maximum daily dose not to exceed 1 gram/day.
    CrCl 15 to 29 mL/minute: 250 mg PO every 8 to 12 hours.
    CrCl 5 to 14 mL/minute and not on dialysis: 250 mg PO every 24 hours.
    CrCl 1 to 4 mL/minute and not on dialysis: 250 mg PO every 48 to 60 hours.
     
    Pediatric renal dosage adjustments based on a usual dose in pediatric patients of 25 to 50 mg/kg/day PO divided every 6 hours
    CrCl greater than 50 mL/minute/1.73 m2: No dosage adjustment needed.
    CrCl 30 to 50 mL/minute/1.73 m2: 5 to 10 mg/kg/dose PO every 8 hours.
    CrCl 10 to 29 mL/minute/1.73 m2: 5 to 10 mg/kg/dose PO every 12 hours.
    CrCl less than 10 mL/minute/1.73 m2: 5 to 10 mg/kg/dose PO every 24 hours.
     
    Intermittent hemodialysis
    Adults: For patients receiving intermittent hemodialysis, dose after dialysis.
    Pediatric patients: 5 to 10 mg/kg/dose PO every 24 hours, after hemodialysis.
     
    Peritoneal dialysis
    For mild infections (adults): 250 to 500 mg PO every 12 to 24 hours.
    For mild infections (pediatric patients): 5 to 10 mg/kg/dose PO every 24 hours.
    For exit-site and tunnel infections (adults): 500 mg PO every 8 to 12 hours.
    For exit-site and tunnel infections (pediatric patients): 10 to 20 mg/kg/day given in 1 or 2 doses (Max: 1 gram/day).

    ADMINISTRATION

    Oral Administration

    Cephalexin is administered orally. All dosage forms may be administered without regard to meals.
    Cephalexin and cephalexin hydrochloride are commercially available as monohydrates; the dosage is expressed as cephalexin base.

    Oral Solid Formulations

    Capsules: Swallow whole with a drink of water.

    Oral Liquid Formulations

    Oral suspension: Shake well prior to each use. To ensure accurate dosage, measure dose with a calibrated oral syringe, spoon, or measuring cup.
     
    Reconstitution of oral suspension:
    Follow the manufacturer's directions for mixing; the water volume is usually added in 2 aliquots, shaking well after each addition. 
    After mixing, store oral suspension in a refrigerator. May be kept for 14 days without significant loss of potency. Shake well before using. Keep tightly closed.

    STORAGE

    Generic:
    - Store at room temperature (between 59 to 86 degrees F)
    Biocef:
    - Store at controlled room temperature (between 68 and 77 degrees F)
    - Store reconstituted product in refrigerator (36 to 46 degrees F), discard after 14 days
    Daxbia :
    - Store between 68 to 77 degrees F, excursions permitted 59 to 86 degrees F
    Keflex:
    - Store at controlled room temperature (between 68 and 77 degrees F)
    - Store reconstituted product in refrigerator (36 to 46 degrees F), discard after 14 days
    Panixine:
    - Store at controlled room temperature (between 68 and 77 degrees F)

    CONTRAINDICATIONS / PRECAUTIONS

    Antimicrobial resistance, viral infection

    Cephalexin does not treat viral infection (e.g., common cold). Prescribing in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria (antimicrobial resistance). Patients should be told to complete the full course of treatment, even if they feel better earlier.

    Cephalosporin hypersensitivity, penicillin hypersensitivity

    Cephalexin is contraindicated for use in patients with cephalosporin hypersensitivity. Cephalosporins cause hypersensitivity reactions in <= 5% of patients receiving them. A variety of hypersensitivity reactions ranging from mild rash to fatal anaphylaxis may occur. Serum sickness reactions are a form of hypersensitivity to cephalosporins and may occur after a second course of cephalosporin therapy. Certain individuals may be more susceptible to allergic reactions to cephalosporins. The structural similarity between cephalexin and penicillin means that cross-reactivity can occur. The incidence of cross-reactivity to cephalosporins is approximately up to 10% in patients with a documented history of allergy to penicillin. Cephalexin should be administered with caution to individuals with a history of hypersensitivity to penicillin. Patients who have experienced severe, immediate-type penicillin hypersensitivity (e.g., acute bronchospasm, anaphylaxis, severe dermatologic reactions) should not receive cephalexin. The health care professional should have immediate availability of agents used in the treatment of severe anaphylaxis in the event of a serious allergic reaction to cephalexin.

    Renal failure, renal impairment

    Cephalexin should be used with caution in patients with renal impairment or renal failure since the drug is eliminated via renal mechanisms. The degree of renal impairment and the severity of the infection will determine if renal dose adjustments or dosage interval adjustments are required. Dosages may need to be reduced in these patients. Cephalexin may rarely worsen renal function; pre-existing renal impairment may increase the risk of drug-induced renal toxicity.

    Colitis, diarrhea, GI disease, inflammatory bowel disease, pseudomembranous colitis, ulcerative colitis

    Prolonged use of cephalexin may result in overgrowth of nonsusceptilble organisms. Observe the patient for signs of a superinfection, particularly with Candida or Clostridium difficile. Antibacterial agents have been associated with pseudomembranous colitis (antibiotic-associated colitis) which may range in severity from mild to life-threatening. In the colon, overgrowth of Clostridia may exist when normal flora is altered subsequent to antibacterial administration. The toxin produced by Clostridium difficile is a primary cause of pseudomembranous colitis. It is known that systemic use of antibiotics predisposes patients to development of pseudomembranous colitis. Consideration should be given to the diagnosis of pseudomembranous colitis in patients presenting with diarrhea following antibacterial administration. Systemic antibiotics should be prescribed with caution to patients with inflammatory bowel disease such as ulcerative colitis or other GI disease. If diarrhea develops during therapy, the drug should be discontinued. Following diagnosis of pseudomembranous colitis, therapeutic measures should be instituted. In milder cases, the colitis may respond to discontinuation of the offending agent. In moderate to severe cases, fluids and electrolytes, protein supplementation, and treatment with an antibacterial effective against Clostridium difficile may be warranted. Products inhibiting peristalsis are contraindicated in this clinical situation. Practitioners should be aware that antibiotic-associated colitis has been observed to occur over two months or more following discontinuation of systemic antibiotic therapy; a careful medical history should be taken.

    Breast-feeding

    According to the manufacturer, cephalexin should be used with caution during breast-feeding. Most cephalosporins, including cephalexin, are excreted in breast milk in small quantities. After a 500 mg dose, the excretion of cephalexin in human milk increased up to 4 hours after the dose and reached a maximum concentration of 4 mcg/ml. The concentration then decreased gradually and was undetectable 8 hours after administration. In one mother being treated for a breast infection with cephalexin (500 mg PO q6h) and probenecid (500 mg PO q6h), breast milk concentrations of cephalexin and probenecid were 0.745 and 0.964 mcg/ml, respectively. These concentrations correspond to infant doses of 112 mcg/kg/day for cephalexin and 145 mcg/kg/day probenecid assuming a milk consumption of 150 ml/kg/day. This dose of cephalexin is significantly lower (i.e. < 1%) than doses prescribed for infants and children. In this case report, the nursing infant had severe diarrhea and discomfort and was crying; it is unclear whether these same effects would have been seen with cephalexin monotherapy. As with other oral antibiotics, alterations in the infant gut flora resulting in diarrhea may be expected; however, significant systemic effects do not appear to be common. Although the American Academy of Pediatrics (AAP) has not evaluated the use of cephalexin during breast-feeding, the AAP considers several other cephalosporins, such as cefazolin, cefprozil, and cefadroxil, to be usually compatible with breast-feeding. Consider the benefits of breast-feeding, the risk of potential drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding baby experiences an adverse effect related to a maternally ingested drug, healthcare providers are encouraged to report the adverse effect to the FDA.

    Pregnancy

    Cephalexin is classified in FDA pregnancy risk category B. Animal data suggest that cephalexin does not impair fertility or cause harm to the fetus. Cephalexin does cross the placenta and distributes to fetal tissues. However, there are no adequate and well-controlled studies in pregnant women. Because limited data are available, cephalexin should be used during pregnancy only if clearly needed.

    Coagulopathy, vitamin K deficiency

    All cephalosporins, including cephalexin, may rarely cause hypothrombinemia and have the potential to cause bleeding. The mechanism is usually via the inhibition of normal gut flora and decreases in normal vitamin K synthesis, leading to coagulopathy. Cephalosporins which contain the NMTT side chain (i.e., cefoperazone, cefamandole, cefotetan) have been associated with an increased risk of hypoprothrombinemia. Cephalosporins should be used cautiously when there is a need for prolonged antibiotic therapy or other risk factors (e.g., malnutrition). Patients with a preexisting coagulopathy (e.g., vitamin K deficiency) may be at higher risk for developing bleeding complications.

    Diabetes mellitus

    Cephalosporins have also been reported to cause false-positive results in urine glucose tests that contain cupric sulfate solution (e.g., Benedict's reagent, Clinitest); patients with diabetes mellitus who use urinary testing methods may receive caution regarding this interference. In addition, positive direct Coombs' tests have been reported in patients receiving cephalosporins, including cephalexin. If hematological testing is done in patients receiving cephalosporins, a false-positive Coombs' test may be caused by the antibiotic.

    Geriatric

    Cephalexin is renally eliminated. In clinical studies of cephalexin, no overall differences in safety or effectiveness were observed between geriatric and younger adults. However, because geriatric patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function. The federal Omnibus Budget Reconciliation Act (OBRA) regulates medication use in residents of long-term care facilities. According to OBRA, use of antibiotics should be limited to confirmed or suspected bacterial infections. Antibiotics are non-selective and may result in the eradication of beneficial microorganisms while promoting the emergence of undesired ones, causing secondary infections such as oral thrush, colitis, or vaginitis. Any antibiotic may cause diarrhea, nausea, vomiting, anorexia, and hypersensitivity reactions.

    ADVERSE REACTIONS

    Severe

    interstitial nephritis / Delayed / 0-1.0
    seizures / Delayed / 0-1.0
    hemolytic anemia / Delayed / 0-1.0
    anaphylactoid reactions / Rapid / 0-0.1
    erythema multiforme / Delayed / Incidence not known
    Stevens-Johnson syndrome / Delayed / Incidence not known
    angioedema / Rapid / Incidence not known
    toxic epidermal necrolysis / Delayed / Incidence not known
    acute generalized exanthematous pustulosis (AGEP) / Delayed / Incidence not known
    aplastic anemia / Delayed / Incidence not known
    pancytopenia / Delayed / Incidence not known
    agranulocytosis / Delayed / Incidence not known

    Moderate

    eosinophilia / Delayed / 2.7-8.2
    elevated hepatic enzymes / Delayed / 1.0-7.0
    thrombocytopenia / Delayed / 0-3.0
    neutropenia / Delayed / 0-1.0
    hypoprothrombinemia / Delayed / 0-1.0
    pseudomembranous colitis / Delayed / Incidence not known
    jaundice / Delayed / Incidence not known
    hepatitis / Delayed / Incidence not known
    gastritis / Delayed / Incidence not known
    vaginitis / Delayed / Incidence not known
    superinfection / Delayed / Incidence not known
    hallucinations / Early / Incidence not known
    leukopenia / Delayed / Incidence not known
    candidiasis / Delayed / Incidence not known
    confusion / Early / Incidence not known
    bleeding / Early / Incidence not known

    Mild

    vomiting / Early / 0-5.0
    diarrhea / Early / 0-5.0
    nausea / Early / 0-5.0
    rash (unspecified) / Early / 1.0-3.0
    urticaria / Rapid / 1.0-3.0
    maculopapular rash / Early / 1.0-3.0
    abdominal pain / Early / Incidence not known
    dyspepsia / Early / Incidence not known
    arthralgia / Delayed / Incidence not known
    pruritus / Rapid / Incidence not known
    fever / Early / Incidence not known
    dizziness / Early / Incidence not known
    fatigue / Early / Incidence not known
    agitation / Early / Incidence not known
    pruritus ani / Early / Incidence not known
    headache / Early / Incidence not known

    DRUG INTERACTIONS

    Alogliptin; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Azelaic Acid; Copper; Folic Acid; Nicotinamide; Pyridoxine; Zinc: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.
    Canagliflozin; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Carbetapentane; Guaifenesin; Phenylephrine: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.
    Carbetapentane; Phenylephrine: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.
    Chlorpheniramine; Pseudoephedrine: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.
    Cholestyramine: (Minor) Caution may be warranted with coadministration of cephalexin and cholestyramine as cephalexin absorption may be decreased. In a study comparing patients receiving cephalexin alone with cephalexin plus cholestyramine, cephalexin mean and peak plasma concentrations were significantly reduced in patients with malabsorption syndromes.
    Dapagliflozin; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Dienogest; Estradiol valerate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Drospirenone; Estradiol: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Drospirenone; Ethinyl Estradiol: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Drospirenone; Ethinyl Estradiol; Levomefolate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Empagliflozin; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Estradiol; Levonorgestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Estradiol; Norethindrone: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Estradiol; Norgestimate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Desogestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Ethynodiol Diacetate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Etonogestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Levonorgestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Levonorgestrel; Folic Acid; Levomefolate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norelgestromin: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norethindrone Acetate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norethindrone Acetate; Ferrous fumarate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norethindrone: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norethindrone; Ferrous fumarate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norgestimate: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Ethinyl Estradiol; Norgestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Glipizide; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Glyburide; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Leuprolide; Norethindrone: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Levonorgestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Linagliptin; Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Loop diuretics: (Moderate) Nephrotoxicity associated with cephalosporins may be potentiated by concomitant furosemide therapy. Clinicans should be aware that this may occur even in patients with minor or transient renal impairment.
    Mestranol; Norethindrone: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Metformin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Metformin; Pioglitazone: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Metformin; Repaglinide: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Metformin; Rosiglitazone: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Metformin; Saxagliptin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Metformin; Sitagliptin: (Moderate) In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin Cmax and AUC increased by an average of 34% and 24%, respectively; metformin renal clearance decreased by an average of 14%. No information is available about the interaction of cephalexin and metformin following multiple dose administration.
    Norethindrone: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Norgestrel: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Oral Contraceptives: (Moderate) It would be prudent to recommend alternative or additional contraception when oral contraceptives (OCs) are used in conjunction with antibiotics. It was previously thought that antibiotics may decrease the effectiveness of OCs containing estrogens due to stimulation of metabolism or a reduction in enterohepatic circulation via changes in GI flora. One retrospective study reviewed the literature to determine the effects of oral antibiotics on the pharmacokinetics of contraceptive estrogens and progestins, and also examined clinical studies in which the incidence of pregnancy with OCs and antibiotics was reported. It was concluded that the antibiotics ampicillin, ciprofloxacin, clarithromycin, doxycycline, metronidazole, ofloxacin, roxithromycin, temafloxacin, and tetracycline did not alter plasma concentrations of OCs. Antituberculous drugs (e.g., rifampin) were the only agents associated with OC failure and pregnancy. Based on the study results, these authors recommended that back-up contraception may not be necessary if OCs are used reliably during oral antibiotic use. Another review concurred with these data, but noted that individual patients have been identified who experienced significant decreases in plasma concentrations of combined OC components and who appeared to ovulate; the agents most often associated with these changes were rifampin, tetracyclines, and penicillin derivatives. These authors concluded that because females most at risk for OC failure or noncompliance may not be easily identified and the true incidence of such events may be under-reported, and given the serious consequence of unwanted pregnancy, that recommending an additional method of contraception during short-term antibiotic use may be justified. During long-term antibiotic administration, the risk for drug interaction with OCs is less clear, but alternative or additional contraception may be advisable in selected circumstances. Data regarding progestin-only contraceptives or for newer combined contraceptive deliveries (e.g., patches, rings) are not available.
    Probenecid: (Minor) Probenecid competitively inhibits renal tubular secretion of cephalexin, causing higher, prolonged serum levels of the drug.
    Sodium picosulfate; Magnesium oxide; Anhydrous citric acid: (Major) Prior or concomitant use of antibiotics with sodium picosulfate; magnesium oxide; anhydrous citric acid may reduce efficacy of the bowel preparation as conversion of sodium picosulfate to its active metabolite bis-(p-hydroxy-phenyl)-pyridyl-2-methane (BHPM) is mediated by colonic bacteria. If possible, avoid coadministration. Certain antibiotics (i.e., tetracyclines and quinolones) may chelate with the magnesium in sodium picosulfate; magnesium oxide; anhydrous citric acid solution. Therefore, these antibiotics should be taken at least 2 hours before and not less than 6 hours after the administration of sodium picosulfate; magnesium oxide; anhydrous citric acid solution.
    Warfarin: (Moderate) The concomitant use of warfarin with many classes of antibiotics, including cephalosporins, may increase the INR thereby potentiating the risk for bleeding. Inhibition of vitamin K synthesis due to alterations in the intestinal flora may be a mechanism; however, concurrent infection is also a potential risk factor for elevated INR. Additionally, certain cephalosporins (cefotetan, cefoperazone, cefamandole) are associated with prolongation of the prothrombin time due to the methylthiotetrazole (MTT) side chain at the R2 position, which disturbs the synthesis of vitamin K-dependent clotting factors in the liver. Monitor patients for signs and symptoms of bleeding. Additionally, increased monitoring of the INR, especially during initiation and upon discontinuation of the antibiotic, may be necessary.
    Zinc Salts: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.
    Zinc: (Minor) Caution may be warranted with coadminstration of cephalexin and zinc salts as zinc may decrease the absorption of cephalexin. In a randomized, single-dose, four-way crossover study (n = 12), patients received cephalexin alone, in combination with zinc sulfate (250 mg), 3 hours after zinc sulfate, or 3 hours before zinc sulfate. When administered in combination with zinc, the cephalexin Cmax decreased from 18.07 +/- 4.27 mcg/ml to 12.46 +/- 2.73 mcg/ml (p < 0.05) and the AUC decreased from 41.97 +/- 6.04 mcg x h/ml to 30.47 +/- 3.52 mcg x h/ml (p < 0.05). When cephalexin was administered 3 hours after zinc, the Cmax and AUC were 16 +/- 4.06 mcg/ml (p < 0.05) and 34.37 +/- 1.58 mcg x h/mL (p < 0.05), respectively. When cephalexin was administered 3 hours before zinc, there were no significant differences in the cephalexin Cmax or AUC. One in vitro study suggested that zinc is a competitive inhibitor of the intestinal peptide transporter, PEPT1, which may inhibit the uptake of oral cephalosporins. An additional in vitro study suggested that trace elements may have an antagonistic effect on cephalosporins.

    PREGNANCY AND LACTATION

    Pregnancy

    Cephalexin is classified in FDA pregnancy risk category B. Animal data suggest that cephalexin does not impair fertility or cause harm to the fetus. Cephalexin does cross the placenta and distributes to fetal tissues. However, there are no adequate and well-controlled studies in pregnant women. Because limited data are available, cephalexin should be used during pregnancy only if clearly needed.

    According to the manufacturer, cephalexin should be used with caution during breast-feeding. Most cephalosporins, including cephalexin, are excreted in breast milk in small quantities. After a 500 mg dose, the excretion of cephalexin in human milk increased up to 4 hours after the dose and reached a maximum concentration of 4 mcg/ml. The concentration then decreased gradually and was undetectable 8 hours after administration. In one mother being treated for a breast infection with cephalexin (500 mg PO q6h) and probenecid (500 mg PO q6h), breast milk concentrations of cephalexin and probenecid were 0.745 and 0.964 mcg/ml, respectively. These concentrations correspond to infant doses of 112 mcg/kg/day for cephalexin and 145 mcg/kg/day probenecid assuming a milk consumption of 150 ml/kg/day. This dose of cephalexin is significantly lower (i.e. < 1%) than doses prescribed for infants and children. In this case report, the nursing infant had severe diarrhea and discomfort and was crying; it is unclear whether these same effects would have been seen with cephalexin monotherapy. As with other oral antibiotics, alterations in the infant gut flora resulting in diarrhea may be expected; however, significant systemic effects do not appear to be common. Although the American Academy of Pediatrics (AAP) has not evaluated the use of cephalexin during breast-feeding, the AAP considers several other cephalosporins, such as cefazolin, cefprozil, and cefadroxil, to be usually compatible with breast-feeding. Consider the benefits of breast-feeding, the risk of potential drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding baby experiences an adverse effect related to a maternally ingested drug, healthcare providers are encouraged to report the adverse effect to the FDA.

    MECHANISM OF ACTION

    Cephalexin, a beta-lactam antibiotic similar to penicillins, inhibits the third and final stage of bacterial cell wall synthesis by preferentially binding to specific penicillin-binding proteins (PBPs) that are located inside the bacterial cell wall. Penicillin-binding proteins are responsible for several steps in the synthesis of the cell wall and are found in quantities of several hundred to several thousand molecules per bacterial cell. Penicillin-binding proteins vary among different bacterial species. Thus, the intrinisic activity of cephalexin as well as the other cephalosporins and penicillins against a particular organism depends on its ability to gain access to and bind with the necessary PBP. Like all beta-lactam antibiotics, cephalexin's ability to interfere with PBP-mediated cell wall synthesis ultimately leads to cell lysis. Lysis is mediated by bacterial cell wall autolytic enzymes (i.e., autolysins). The relationship between PBPs and autolysins is unclear, but it is possible that the beta-lactam antibiotic interferes with an autolysin inhibitor.
     
    Beta-lactams, including cephalexin, exhibit concentration-independent or time-dependent killing. In vitro and in vivo animal studies have demonstrated that the major pharmacodynamic parameter that determines efficacy for beta-lactams is the amount of time free (non-protein bound) drug concentrations exceed the minimum inhibitory concentration (MIC) of the organism (free T > MIC). This microbiological killing pattern is due to the mechanism of action, which is acylation of PBPs. There is a maximum proportion of PBPs that can be acylated; therefore, once maximum acylation has occurred, killing rates cannot increase. Free beta-lactam concentrations do not have to remain above the MIC for the entire dosing interval. The percentage of time required for both bacteriostatic and maximal bactericidal activity is different for the various classes of beta-lactams. Cephalosporins require free drug concentrations to be above the MIC for 35—40% of the dosing interval for bacteriostatic activity and 60—70% of the dosing interval for bactericidal activity.
     
    The manufacturer and the Clinical and Laboratory Standards Institute (CLSI) define MICs as susceptible at concentrations <= 8 mcg/mL, intermediate at concentrations of 16 mcg/mL, and resistant at concentrations >= 32 mcg/mL.

    PHARMACOKINETICS

    Cephalexin is administered orally. Approximately 10—15% of the circulating drug is protein-bound. Cephalexin is distributed into most body tissues and fluids but does not reach therapeutic levels within the CSF. It crosses the placenta. A small percentage is excreted in breast milk.
     
    Cephalexin is not metabolized and largely excreted unchanged into the urine, which leads to high urinary concentrations. Approximately 50—60% of the dose appears unchanged in the urine during the first 2 hours and 80—100% of dose appears unchanged in the urine after 6—8 hours. One-third of plasma clearance is by glomerular filtration and the other two-thirds by tubular excretion. The elimination half-life is approximately 1 hour in patients with normal renal function.
     
    Affected cytochrome P450 isoenzymes: none

    Oral Route

    Cephalexin is acid-stable. It is rapidly absorbed in the upper intestine after oral administration. There may be a delay in absorption when cephalexin is administered with food resulting in lower peak concentrations as compared to a fasting state. However, serum concentrations are more prolonged resulting in similar areas under the curve. After doses of 250 mg, 500 mg, and 1 g, average peak serum levels of approximately 9, 18, and 32 mcg/mL, respectively were obtained at 1 hour.