Trade Names:Dilantin Infatab- Tablets, chewable 50 mg
Trade Names:Dilantin-125- Suspension, oral 125 mg/5 mLPhenytoin Sodium
Trade Names:Dilantin- Injection 50 mg/mL (46 mg phenytoin)
Trade Names:Dilantin Kapseals- Capsules 30 mg (27.6 mg phenytoin)- Capsules 100 mg (92 mg phenytoin)Dilantin Capsules (Canada)Dilantin-30 Suspension (Canada)Taro-Phenytoin (Canada)
Appears to act at motor cortex in inhibiting spread of seizure activity. Possibly works by promoting sodium efflux from neurons, thereby stabilizing threshold against hyperexcitability. Also decreases posttetanic potentiation at synapse.
Slow and variable (oral); poor in neonates; rapid (IV); slow but complete (IM). Steady state is 7 to 10 days. T max is 4 to 12 h ( Kapseals ); 1.5 to 3 h ( Infatabs , Dilantin-125 oral suspension).
Distributes into CSF, saliva, semen, GI fluids, bile, breast milk, and crosses the placenta. Protein binding is high (more than 90%) but may be lower in neonates (84%).
Hydroxylated in the liver by an enzyme system, which is saturable at high plasma levels.
Mostly excreted in bile as inactive metabolites, then reabsorbed from the intestinal tract and excreted in the urine (as metabolites). Plasma t 1/2 is 22 h (oral phenytoin) and 14 h ( Infatabs ). Excretion is enhanced by alkaline urine.
Control of grand mal and psychomotor seizures; prevention and treatment of seizures occurring during or after neurosurgery; control of grand mal type of status epilepticus (parenteral administration).
Control of arrhythmias, (particularly cardiac glycoside-induced arrhythmias); control of convulsions in severe preeclampsia; treatment of trigeminal neuralgia (tic douloureux), recessive dystrophic epidermolysis bullosa and junctional epidermolysis bullosa.
Hypersensitivity to phenytoin or other hydantoins; sinoatrial block; sinus bradycardia; second- and third-degree atrioventricular block; Adams-Stokes syndrome.
Individualize dose within clinically effective therapeutic serum level of 10 to 20 mcg/mL.SeizuresAdults
PO 100 mg (or 125 mg of suspension) 3 times daily initially.Maintenance
300 to 400 mg/day (max, 600 mg/day). Sometimes initial 1 g loading dose is divided into 3 doses (400, 300, and 300 mg) and is given at 2-h intervals. Once seizure control is established, extended-release form (300 mg) may be administered for once-a-day dosing.Children
PO 5 mg/kg/day in 2 to 3 divided doses initially.Maintenance
4 to 8 mg/kg/day (max, 300 mg/day).Status EpilepticusAdults
IV Loading dose of 10 to 15 mg/kg via slow IV. Then PO/IV 100 mg every 6 to 8 h.Children
IV Loading dose of 15 to 20 mg/kg at rate not exceeding 1 to 3 mg/kg/min.Neurosurgery ProphylaxisAdults
IM 100 to 200 mg at 4-h intervals during surgery and postoperatively.
May increase hepatotoxicity potential with chronic phenytoin use.Amiodarone, chloramphenicol, disulfiram, estrogens, felbamate, fluconazole, isoniazid, cimetidine, trimethoprim, phenylbutazone, oxyphenbutazone, phenacemide, sulfonamides
May increase phenytoin serum levels.Carbamazepine, sucralfate, antineoplastic agents, rifampin, rifabutin
May decrease phenytoin serum levels.Corticosteroids, coumarin anticoagulants, doxycycline, estrogens, levodopa, felodipine, methadone, loop diuretics, oral contraceptives, quinidine, rifampin, rifabutin
May impair effects of these agents.Cyclosporine
May reduce cyclosporine levels.Disopyramide
May cause decreased disopyramide levels and bioavailability and may enhance anticholinergic actions.Enteral nutritional therapy
May reduce phenytoin concentrations.Folic acid
May cause folic acid deficiency.Metyrapone
Phenytoin may cause subnormal response to metyrapone.Mexiletine
May decrease mexiletine levels and effects.Nondepolarizing muscle relaxants
May cause these agents to have shorter duration or decreased effects.Phenobarbital, sodium valproate, valproic acid
May increase or decrease phenytoin levels. Phenytoin may increase phenobarbital and decrease valproic acid levels.Primidone
May increase concentrations of primidone and metabolites.Sympathomimetics (eg, dopamine)
May cause profound hypotension and possibly cardiac arrest.Theophyllines
Effects of either agent may be decreased.
Do not mix with other drugs in syringe.
Phenytoin may interfere with metapyrone and dexamethasone tests, causing inaccurate results because of increased metabolism of these agents. Drug may cause decreases in serum levels of protein-bound iodine. It may cause increased levels of glucose, alkaline phosphatase and gamma glutamyl transpeptidase.
CV collapse, hypotension, atrial and ventricular conduction depression, ventricular fibrillation (IV use).
Nystagmus; ataxia; dysarthria; slurred speech; mental confusion; dizziness; insomnia; transient nervousness; motor twitching; diplopia; fatigue; irritability; drowsiness; depression; numbness; tremor; headache; choreoathetosis (IV use).
Rashes, sometimes accompanied by fever; bullous, exfoliative or purpuric dermatitis; lupus erythematosus; Stevens-Johnson syndrome; toxic epidermal necrolysis; hirsutism; alopecia.
Nausea; vomiting; diarrhea; constipation.
Thrombocytopenia; leukopenia; granulocytopenia; agranulocytosis; pancytopenia; macrocytosis; megaloblastic anemia; eosinophilia; monocytosis; leukocytosis; simple anemia; hemolytic anemia; aplastic anemia.
Toxic hepatitis and liver damage; hepatocellular degeneration and necrosis; hepatitis; jaundice; nephrosis.
Gingival hyperplasia; coarsening of facial features; lip enlargement; Peyronie's disease; polyarthropathy; hyperglycemia; weight gain; chest pain; IgA depression; fever; photophobia; gynecomastia; periarteritis nodosa; pulmonary fibrosis; tissue injury at injection site; lymph node hyperplasia; hypothyroidism.
Pregnancy category undetermined. Consult health care provider. Possible risk of birth defects must be considered along with risk of seizures to fetus in untreated epileptic mothers.
Excreted in breast milk.
Rapid substitution of alternate therapy may be necessary.
Use drug with caution with hepatic function impairment, acute intermittent porphyria, alcohol abuse, hypotension, and severe myocardial insufficiency.
Because products vary in bioavailability; brand interchange is not recommended.
Drug should not be given to treat seizures due to hypoglycemia or other metabolic causes or petit mal (absence) epilepsy.
Abrupt withdrawal may precipitate status epilepticus. Dosage must be reduced or other anticonvulsant medicine substituted gradually.
Nystagmus, ataxia, dysarthria, hypotension, diminished mental capacity, coma, unresponsive pupils, respiratory and CV depression.
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