Product Details

Phenytoin

A to Z Drug Facts

Phenytoin

Action
Indications
Contraindications
Route/Dosage
Interactions
Lab Test Interferences
Adverse Reactions
PrecautionsPatient Care Considerations
Administration/Storage
Assessment/Interventions
Patient/Family Education

(FEN-ih-toe-in)PhenytoinDilantin Infatab, Dilantin-125Phenytoin SodiumDilantin, Dilantin KapsealsClass: Anticonvulsant/Hydantoin

 Action 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 post-tetanic potentiation at synapse.

 Indications 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). Unlabeled use(s): 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.

 Contraindications Hypersensitivity to phenytoin or other hydantoins; sinoatrial block; sinus bradycardia; second- and third-degree atrioventricular block; Adams-Stokes syndrome.

 Route/Dosage

Individualize dose within clinically effective therapeutic serum level of 10 to 20 mcg/ml.

Seizures

ADULTS: PO 100 mg (or 125 mg of suspension) tid initially. Maintenance: 300 to 400 mg/day (maximum 600 mg/day). Sometimes initial 1 g loading dose is divided into 3 doses (400 mg, 300 mg, and 300 mg) and is given at 2 hr interval). 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 (maximum 300 mg/day).

Status Epilepticus

ADULTS: IV Loading dose of 10 to 15 mg/kg via slow IV. Then PO/IV 100 mg q 6 to 8 hr. CHILDREN: IV Loading dose of 15 to 20 mg/kg at rate not exceeding 1 to 3 mg/kg/min.

Neurosurgery Prophylaxis

ADULTS: IM 100 to 200 mg at 4-hr intervals during surgery and postoperatively.

 Interactions

Acetaminophen: 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.

 Lab Test Interferences 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. Incompatibilities: Do not mix with other drugs in syringe.

 Adverse Reactions

CV: (IV use): CV collapse; hypotension; atrial and ventricular conduction depression; ventricular fibrillation. CNS: Nystagmus; ataxia; dysarthria; slurred speech; mental confusion; dizziness; insomnia; transient nervousness; motor twitching; diplopia; fatigue; irritability; drowsiness; depression; numbness; tremor; headache; choreoathetosis (IV use). DERM: Rashes, sometimes accompanied by fever; bullous, exfoliative or purpuric dermatitis; lupus erythematosus; Stevens-Johnson syndrome; toxic epidermal necrolysis; hirsutism; alopecia. EENT: Conjunctivitis. GI: Nausea; vomiting; diarrhea; constipation. HEMA: Thrombocytopenia; leukopenia; granulocytopenia; agranulocytosis; pancytopenia; macrocytosis; megaloblastic anemia; eosinophilia; monocytosis; leukocytosis; simple anemia; hemolytic anemia; aplastic anemia. HEPA: Toxic hepatitis and liver damage; hepatocellular degeneration and necrosis; hepatitis; jaundice; nephrosis. OTHER: 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.

 Precautions

Pregnancy: Pregnancy category undetermined. Consult physician. Possible risk of birth defects must be considered along with risk of seizures to fetus in untreated epileptic mothers. Lactation: Excreted in breast milk. Special-risk patients: Use drug with caution with hepatic impairment, acute intermittent poryphria, alcohol abuse, hypotension, and severe myocardial insufficiency. Bioavailability: Because products vary in bioavailability; brand interchange is not recommended. Hypersensitivity reactions: Rapid substitution of alternate therapy may be necessary. Seizures: Drug should not be given to treat seizures due to hypoglycemia or other metabolic causes or petit mal (absence) epilepsy. Withdrawal: Abrupt withdrawal may precipitate status epilepticus. Dosage must be reduced or other anticonvulsant medicine substituted gradually.

PATIENT CARE CONSIDERATIONS

 

 Administration/Storage

• Shake oral suspension well.
• Do not administer discolored capsules.
• Administer oral forms with food.
• Only extended-release capsules are recommended for once-a-day dosage.
• Do not crush or allow patient to chew extended-release capsules.
• Do not substitute one brand for another; bioequivalence problems exist.
• For parenteral administration, direct IV administration is recommended.
• Administer IV into large vein via large-gauge needle or cannula. Do not exceed rate of 50 mg/min for adults or 1 to 3 mg/kg/min in neonates. Immediately flush with normal saline solution. Avoid continuous infusion.
• Monitor BP for possible hypotension during IV infusion. Rate of infusion may need to be decreased.
• Avoid IM route when possible. If IM administration is needed for > 1 wk, consider alternatives such as gastric intubation.
• When patient is stabilized with oral phenytoin and switched from oral to IM route, dose must be increased by 50%. When patient returns to oral form after IM administration, ½ original oral dose should be given for 1 wk.
• Do not abruptly discontinue medication; withdrawal must be slowly tapered.
• Do not use parenteral solution if precipitates form that will not dissolve at room temperature.
• Do not use parenteral solution if it is hazy; faint, clear yellow color is acceptable for use.

 Assessment/Interventions

• Obtain patient history, including drug history and any known allergies. Note hepatic impairment, cardiac disease and porphyria.
• Perform blood counts and urinalyses on initiation of therapy and at monthly intervals for several months.
• Observe for rash, which may signify hypersensitivity reaction that can lead to serious dermatological reactions. If rash occurs, withhold drug and notify physician.
• Monitor ECG and BP continuously.
• Monitor for elevated blood glucose values in diabetic patients and report to physician.
• Observe for side effects including nystagmus, ataxia, drowsiness, severe nausea or vomiting, gingival hyperplasia or jaundice, and report to physician.

OVERDOSAGE: SIGNS & SYMPTOMS Nystagmus, ataxia, dysarthria, hypotension, diminished mental capacity, coma, unresponsive pupils, respiratory and cardiovascular depression

 Patient/Family Education

• Advise patient to take medication with food.
• Teach patient to shake oral suspension well.
• Instruct patient taking capsules not to use discolored ones.
• Tell patient to notify physician if skin rash develops.
• Instruct patient to report the following symptoms to physician: Nystagmus, ataxia, drowsiness, severe nausea or vomiting, gingival hyperplasia, or jaundice.
• Caution patient to consult with physician before using alcohol or taking any other drug including otc medications.
• Warn patient that stopping medication too quickly may precipitate seizures. Stress that dose should be changed only under physician's direction.
• Inform patient that it is important to maintain good oral hygiene and to inform dentist of phenytoin therapy.
• Instruct diabetic patient that changes may occur in blood sugars and to monitor and report any abnormal results to physician.
• Inform patient that urine may turn pink.
• Advise patient to carry identification such as Medi-Alert that identifies illness and medication.
• Warn patient to inform surgeon, physician, or dentist about this medication before any surgical, emergency, or dental procedure.
• Advise patient that drug may cause drowsiness, and to use caution while driving or performing other tasks requiring mental alertness.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts