PHENYTOIN
(fen'i-toy-in)
Dilantin-125, Dilantin-30 Pediatric, Dilantin Infatab
PHENYTOIN SODIUM EXTENDED
Dilantin Kapseals
PHENYTOIN SODIUM PROMPT
Dilantin
Classifications: central nervous system agent; anticonvulsant; hydantoin
Pregnancy Category: D

Availability

100 mg prompt release capsule; 30 mg, 100 mg sustained release capsule; 50 mg chewable tablet; 125 mg/5 mL suspension; 50 mg/mL injection

Actions

Hydantoin derivative chemically related to phenobarbital. Precise mechanism of anticonvulsant action is not known, but drug use is accompanied by reduced voltage, frequency, and spread of electrical discharges within the motor cortex. Class IB antiarrhythmic properties similar to those of lidocaine and tocainide (also class IB agents). Has class IB antiarrhythmic properties.

Therapeutic Effects

Inhibits seizure activity. In abnormal tissue causes slight increase in AV conduction velocity depressed by digitalis glycoside; prolongs effective refractory period, suppresses ventricular pacemaker automaticity, and may slow conduction or cause complete block in abnormal ventricular fibers.

Uses

To control tonic-clonic (grand mal) seizures, psychomotor and nonepileptic seizures (e.g., Reye's syndrome, after head trauma). Also used to prevent or treat seizures occurring during or after neurosurgery. Is not effective for absence seizures.

Unlabeled Uses

Antiarrhythmic agent (phenytoin IV) especially in treatment of digitalis-induced arrhythmias; treatment of trigeminal neuralgia (tic douloureux).

Contraindications

Hypersensitivity to hydantoin products; rash; seizures due to hypoglycemia; sinus bradycardia, complete or incomplete heart block; Adams-Stokes syndrome; pregnancy (category D), lactation.

Cautious Use

Impaired liver or kidney function; alcoholism; blood dyscrasias; hypotension, heart block, bradycardia, severe myocardial insufficiency, impending or frank heart failure; older adult, debilitated, gravely ill patients; pancreatic adenoma; diabetes mellitus, hyperglycemia; respiratory depression; acute intermittent porphyria.

Route & Dosage

Anticonvulsant
Adult: PO 15–18 mg/kg or 1 g loading dose, then 300 mg/d in 1–3 divided doses, may be gradually increased by 100 mg/wk until seizures are controlled IV 15–18 mg/kg or 1 g loading dose, then 100 mg t.i.d.
Child: PO/IV 15–20 mg/kg loading dose, then 5 mg/kg or 250 mg/m2 in 2–3 divided doses

Administration

Oral
Intravenous
  • Note: Verify correct rate of IV injection for administration to infants or children with physician.
  • Inspect solution prior to use. May use a slightly yellowed injectable solution safely. Precipitation may be caused by refrigeration, but slow warming to room temperature restores clarity.

PREPARE: Direct: Give undiluted. Use only when clear without precipitate.  

ADMINISTER: Direct: Give 50 mg or fraction thereof over 1 min (25 mg/min in older adult or when used as antiarrhythmic). Follow with an injection of sterile saline through the same in-place catheter or needle. Do not use solutions containing dextrose.  

INCOMPATIBILITIES Solution/additive: 5% dextrose, amikacin, aminophylline, bretylium, cephapirin, codeine phosphate, dobutamine, hydromorphone, insulin, levorphanol, lidocaine, lincomycin, meperidine, metaraminol, methadone, morphine, nitroglycerin, norepinephrine, pentobarbital, procaine, secobarbital, streptomycin, sufentanil. Y-site: Amikacin, amphotericin B cholesteryl complex, bretylium, ciprofloxacin, clindamycin, diltiazem, dobutamine, enalaprilat, lidocaine, heparin, hydromorphone, potassium chloride, propofol, sufentanil, theophylline, TPN, vitamin B complex with C.

  • Observe injection site frequently during administration to prevent infiltration. Local soft tissue irritation may be serious, leading to erosion of tissues.

Adverse Effects (1%)

CNS: Usually dose-related: Nystagmus, drowsiness, ataxia, dizziness, mental confusion, tremors, insomnia, headache, seizures. CV: Bradycardia, hypotension, cardiovascular collapse, ventricular fibrillation, phlebitis. Special Senses: Photophobia, conjunctivitis, diplopia, blurred vision. GI: Gingival hyperplasia, nausea, vomiting, constipation, epigastric pain, dysphagia, loss of taste, weight loss, hepatitis, liver necrosis. Hematologic: Thrombocytopenia, leukopenia, leukocytosis, agranulocytosis, pancytopenia, eosinophilia; megaloblastic, hemolytic, or aplastic anemias. Metabolic: Fever, hyperglycemia, glycosuria, weight gain, edema, transient increase in serum thyrotropic (TSH) level, osteomalacia or rickets associated with hypocalcemia and elevated alkaline phosphatase activity. Skin: Alopecia, hirsutism (especially in young female); rash: scarlatiniform, maculopapular, urticaria, morbilliform; bullous, exfoliative, or purpuric dermatitis; Stevens-Johnson syndrome, toxic epidermal necrolysis, keratosis, neonatal hemorrhage. Urogenital: Acute renal failure, Peyronie's disease. Respiratory: Acute pneumonitis, pulmonary fibrosis. Body as a Whole: Periarteritis nodosum, acute systemic lupus erythematosus, craniofacial abnormalities (with enlargement of lips); lymphadenopathy.

Diagnostic Test Interference

Phenytoin (hydantoins) may produce lower than normal values for dexamethasone or metyrapone tests; may increase serum levels of glucose, BSP, and alkaline phosphatase and may decrease PBI and urinary steroid levels.

Interactions

Drug: Alcohol decreases phenytoin effects; other anticonvulsants may increase or decrease phenytoin levels; phenytoin may decrease absorption and increase metabolism of oral anticoagulants; phenytoin increases metabolism of corticosteroids, oral contraceptives, and nisoldipine, thus decreasing their effectiveness; amiodarone, chloramphenicol, omeprazole, and ticlopidine increase phenytoin levels; antituberculosis agents decrease phenytoin levels. Food: Folic acid, calcium, and vitamin D absorption may be decreased by phenytoin; phenytoin absorption may be decreased by enteral nutrition supplements. Herbal: Ginkgo may decrease anticonvulsant effectiveness.

Pharmacokinetics

Absorption: Completely absorbed from GI tract. Peak: 1.5–3 h prompt release; 4–12 h sustained release. Distribution: 95% protein bound; crosses placenta; small amount in breast milk. Metabolism: Oxidized in liver to inactive metabolites. Elimination: Metabolites excreted by kidneys. Half-Life: 22 h.

Nursing Implications

Assessment & Drug Effects

Patient & Family Education


Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug