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Tonic-Clonic (Grand Mal) and Psychomotor (Temporal Lobe) Seizures:Initial: (Treatment naive) 125mg (1 tsp) tidTitrate: May increase to 625mg (5 tsp) daily, if necessaryClinically effective serum level is usually 10-20mcg/mL; do not change dose at intervals <7-10 days
May require dose adjustment when switching from product formulated w/ free acid to product formulated w/ Na+ salt and vice versa
Tonic-Clonic (Grand Mal) and Psychomotor (Temporal Lobe) Seizures:Initial: 5mg/kg/day in 2 or 3 equally divided dosesMaint: 4-8mg/kg/dayMax: 300mg/day>6 Years: May require the minimum adult dose (300mg/day)Clinically effective serum level is usually 10-20mcg/mL; do not change dose at intervals <7-10 days
Renal ImpairmentCaution when interpreting total phenytoin plasma concentrations; unbound phenytoin concentrations may be more usefulHepatic ImpairmentCaution when interpreting total phenytoin plasma concentrations; unbound phenytoin concentrations may be more usefulElderlyMay require lower or less frequent dosingOther Important ConsiderationsHypoalbuminemia:Caution when interpreting total phenytoin plasma concentrations; unbound phenytoin concentrations may be more useful
Oral routeUse an accurately calibrated measuring device to ensure accurate dosing.
Oral Sus: 125mg/5mL [237mL]
History of hypersensitivity to phenytoin or its inactive ingredients, or other hydantoins. Coadministration w/ delavirdine.
Unbound concentration of phenytoin may be elevated in patients w/ hyperbilirubinemia. Avoid abrupt withdrawal; may precipitate status epilepticus. May increase risk of suicidal thoughts/behavior; monitor for emergence/worsening of depression, suicidal thoughts/behavior, and/or any unusual changes in mood/behavior. Serious and sometimes fatal dermatologic reactions, including toxic epidermal necrolysis (TEN) and Stevens-Johnson syndrome (SJS), reported; d/c at 1st sign of rash, unless the rash is clearly not drug-related. Do not resume therapy, and consider alternative therapy if signs/symptoms suggest SJS/TEN. Consideration should be given to avoid use as an alternative for carbamazepine in patients positive for HLA-B*1502. Drug reaction w/ eosinophilia and systemic symptoms (DRESS)/multiorgan hypersensitivity reported; evaluate immediately if signs and symptoms (eg, rash, fever, lymphadenopathy) are present and d/c if an alternative etiology cannot be established. Consider alternatives to structurally similar drugs (eg, carboxamides, barbiturates, succinimides, oxazolidinediones) in patients who have experienced phenytoin hypersensitivity. Acute hepatotoxicity (eg, acute hepatic failure) reported; d/c immediately and do not readminister. Hematopoietic complications and lymphadenopathy reported; extended follow-up observation is indicated and every effort should be made to achieve seizure control using alternative antiepileptic drugs in all cases of lymphadenopathy. Decreased bone mineral density and bone fractures reported during chronic use; consider screening w/ bone-related laboratory and radiological tests as appropriate and initiating treatment plans according to established guidelines. Caution w/ porphyria, hepatic impairment, and in elderly or gravely ill patients. An increase in seizure frequency may occur during pregnancy due to altered phenytoin pharmacokinetics. May cause fetal harm. Bleeding disorder in newborns may occur; give vitamin K to mother before delivery and to neonate after birth. Check plasma levels immediately if early signs of dose-related CNS toxicity develop. Hyperglycemia reported; may increase serum glucose levels in diabetics. Not indicated for seizures due to hypoglycemia or other metabolic causes. Not effective for absence (petit mal) seizures; if tonic-clonic (grand mal) and absence (petit mal) seizures are present, combined drug therapy is needed. Serum levels of phenytoin sustained above the optimal range may produce confusional states or rarely irreversible cerebellar dysfunction and/or cerebellar atrophy; reduce dose if plasma levels are excessive and d/c if symptoms persist. Lab test interactions may occur.
Rash, nystagmus, ataxia, slurred speech, decreased coordination, somnolence, mental confusion, dizziness, insomnia, transient nervousness, motor twitching, acute hepatic failure, thrombocytopenia, altered taste sensation, Peyronie's disease.
See Contraindications. Acute alcohol intake, amiodarone, antiepileptic agents (eg, ethosuximide, felbamate, oxcarbazepine), azoles (eg, fluconazole, ketoconazole, itraconazole), capecitabine, chloramphenicol, chlordiazepoxide, disulfiram, estrogens, fluorouracil, fluoxetine, fluvastatin, fluvoxamine, H2-antagonists (eg, cimetidine), halothane, isoniazid, methylphenidate, omeprazole, phenothiazines, salicylates, sertraline, succinimides, sulfonamides (eg, sulfamethizole, sulfadiazine, sulfamethoxazole-trimethoprim), ticlopidine, tolbutamide, trazodone, and warfarin may increase levels. Anticancer drugs usually in combination (eg, bleomycin, carboplatin, cisplatin), carbamazepine, chronic alcohol abuse, diazepam, diazoxide, folic acid, fosamprenavir, nelfinavir, reserpine, rifampin, ritonavir (RTV), St. John's wort, sucralfate, vigabatrin, and theophylline may decrease levels. Administration w/ preparations that increase gastric pH (eg, supplements or antacids containing calcium carbonate, aluminum hydroxide, and magnesium hydroxide) may affect absorption; do not take at the same time of day. Phenobarbital, sodium valproate, and valproic acid may increase or decrease levels. May impair efficacy of azoles (eg, fluconazole, ketoconazole, itraconazole), corticosteroids, doxycycline, estrogens, furosemide, irinotecan, oral contraceptives, paclitaxel, paroxetine, quinidine, rifampin, sertraline, teniposide, theophylline, and vitamin D. Increased and decreased PT/INR responses reported w/ warfarin. May decrease levels of active metabolites of albendazole, certain HIV antivirals (eg, efavirenz, lopinavir/RTV, indinavir), antiepileptic agents (eg, carbamazepine, felbamate, lamotrigine), atorvastatin, chlorpropamide, clozapine, cyclosporine, digoxin, fluvastatin, folic acid, methadone, mexiletine, nifedipine, nimodipine, nisoldipine, praziquantel, simvastatin, and verapamil. May decrease levels of amprenavir (active metabolite) when given w/ fosamprenavir alone. May increase levels of amprenavir when given w/ the combination of fosamprenavir and RTV. Resistance to the neuromuscular blocking action of pancuronium, vecuronium, rocuronium, and cisatracurium reported in patients chronically administered phenytoin; monitor closely for more rapid recovery from neuromuscular blockade than expected and infusion rate requirements may be higher. Enteral feeding preparations and/or related nutritional supplements may decrease levels; avoid w/ enteral feeding preparations.
Pregnancy: Category D; physicians are advised to recommend that pregnant patients enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry.Lactation: Phenytoin appears to be secreted in low concentrations in human milk; not for use in nursing.
Hydantoin; inhibits seizure activity by promoting Na+ efflux from neurons, stabilizing the threshold against hyperexcitability caused by excessive stimulation or environmental changes capable of reducing membrane Na+ gradient. Reduces the maximal activity of the brain stem centers responsible for the tonic phase of tonic-clonic (grand mal) seizures.
Absorption: Tmax=1.5-3 hrs. Distribution: Plasma protein binding (high); crosses the placenta; found in breast milk. Metabolism: Liver (hydroxylation). CYP2C9 and CYP2C19. Elimination: Urine; T1/2=22 hrs.
Assess for hypersensitivity to the drug or other hydantoins, alcohol use, hepatic/renal impairment, porphyria, grave illness, seizures due to hypoglycemia or other metabolic causes, absence seizures, any other conditions where treatment is contraindicated or cautioned, pregnancy/nursing status, and possible drug interactions.
Monitor for hypersensitivity reactions, dermatologic reactions, DRESS/multiorgan hypersensitivity, hepatotoxicity, hematopoietic complications, lymphadenopathy, decreased bone mineral density, bone fractures, exacerbation of porphyria, hyperglycemia, and other adverse reactions. Monitor for emergence/worsening of depression, suicidal thoughts/behavior, and/or any unusual changes in mood/behavior. Monitor serum levels when switching from Na+ salt to free acid form and vice versa.
Instruct to read medication guide and to take ud. Advise of the importance of adhering strictly to the prescribed dosage regimen, and of informing the physician of any clinical condition in which it is not possible to take the drug orally as prescribed (eg, surgery). Inform about the early toxic signs and symptoms of potential hematologic, dermatologic, hypersensitivity, or hepatic reactions; instruct to immediately contact physician if these develop. Caution on the use of other drugs or alcoholic beverages w/o first seeking physician's advice. Stress the importance of good dental hygiene to minimize the development of gingival hyperplasia and its complications. Advise to notify physician immediately if depression, suicidal thoughts/behavior, or thoughts about self-harm emerge. Encourage patients to enroll in the NAAED Pregnancy Registry if they become pregnant.
20-25°C (68-77°F). Protect from freezing and light.