phenytoin sodium
phenytoin sodium (extended)
Pregnancy Risk Category D
How supplied
phenytoin
Tablets (chewable): 50 mg
Oral suspension: 125 mg/5 ml
phenytoin sodium
Capsules: 100 mg (92-mg base)
Injection: 50 mg/ml (46-mg base)
phenytoin sodium (extended)
Capsules: 30 mg (27.6-mg base), 100 mg (92-mg base)
Action
Unknown. A hydantoin derivative that probably stabilizes neuronal membranes and limits seizure activity by either increasing efflux or decreasing influx of sodium ions across cell membranes in the motor cortex during generation of nerve impulses.
Indications & dosage
Control of tonic-clonic (grand mal) and complex partial (temporal lobe) seizures--
Adults: highly individualized. Initially, 100 mg P.O. t.i.d., increased in increments of 100 mg P.O. q 2 to 4 weeks until desired response is obtained. Usual range is 300 to 600 mg daily. If patient is stabilized with extended-release capsules, once-daily dosing with 300-mg extended-release capsules is possible as an alternative.
Children: 5 mg/kg or 250 mg/m2 P.O. divided b.i.d. or t.i.d. Maximum daily dose is 300 mg.
For patient requiring a loading dose--
Adults: initially, 1 g P.O. daily divided into three doses and administered at 2-hour intervals. Or, 10 to 15 mg/kg I.V. at a rate not exceeding 50 mg/minute. Normal maintenance dose is instituted 24 hours later.
Children: 5 mg/kg/day P.O. in two or three equally divided doses with subsequent dose individualized to maximum of 300 mg daily.
Prevention and treatment of seizures occurring during neurosurgery--
Adults: 100 to 200 mg I.M. q 4 hours during surgery and continued during postoperative period.
Status epilepticus--
Adults: loading dose of 10 to 15 mg/kg I.V. (1 to 1.5 g may be needed) at a rate not exceeding 50 mg/minute; then maintenance doses of 100 mg P.O. or I.V. q 6 to 8 hours.
Elderly: may require lower dosages.
Children: loading dose of 15 to 20 mg/kg I.V., at a rate not exceeding 1 to 3 mg/kg/
minute; then highly individualized maintenance doses.
Adverse reactions
CNS: ataxia, slurred speech, dizziness, insomnia, nervousness, twitching, headache, mental confusion, decreased coordination.
CV: periarteritis nodosa.
EENT: nystagmus, diplopia, blurred vision, gingival hyperplasia (especially in children).
GI: nausea, vomiting, constipation.
Hematologic: thrombocytopenia, leukopenia, agranulocytosis, pancytopenia, macrocythemia, megaloblastic anemia.
Hepatic: toxic hepatitis, increased serum levels of alkaline phosphatase or gamma-glutamyltransferase.
Metabolic: hyperglycemia.
Musculoskeletal: osteomalacia.
Skin: scarlatiniform or morbilliform rash; bullous or purpuric dermatitis; exfoliative dermatitis; Stevens-Johnson syndrome; lupus erythematosus; hirsutism; toxic epidermal necrolysis; photosensitivity; pain, necrosis, inflammation at injection site; discoloration of skin (purple-glove syndrome) if given by I.V. push in back of hand; hypertrichosis.
Other: lymphadenopathy.
Interactions
Drug-drug. Amiodarone, antihistamines, chloramphenicol, cimetidine, cycloserine, diazepam, disulfiram, isoniazid, phenylbutazone, salicylates, sulfamethizole, valproate: may increase phenytoin activity and toxicity. Monitor patient.
Barbiturates, carbamazepine, dexamethasone, diazoxide, folic acid, rifampin: decreased phenytoin activity. Monitor levels.
Carbamazepine, cardiac glycosides, oral contraceptives, quinidine, theophylline, valproic acid: effects may be decreased by phenytoin. Monitor patient.
Drug-food. Oral tube feedings with Osmolite or Isocal: may interfere with absorption of oral phenytoin. Stop enteral feedings for 2 hours before and 2 hours after phenytoin administration.
Drug-lifestyle. Long-term alcohol use: decreased phenytoin activity. Inform patient that heavy alcohol use may diminish drug's benefits.
Effects on diagnostic tests
Drug may cause reduced serum protein-bound iodine and free thyroxine levels without evidence of hypothyroidism; a slight decrease in urinary 17-hydroxysteroid and 17-ketosteroid levels; increased urine 6-b hydroxycortisol excretion, and decreased values for dexamethasone suppression or metyrapone tests.
Contraindications
Contraindicated in patients with hypersensitivity to hydantoin and in those with sinus bradycardia, SA block, second- or third-degree AV block, or Adams-Stokes syndrome.
Nursing considerations
I.V. administration
Patient teaching
*Liquid contains alcohol. **May contain tartrazine. †Canada ‡Australia §U.K. OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING