Phenytoin
Anti-epileptic · Hydantoin
Indications
Oral: Epilepsy particularly of the grand mal type and psychomotor seizures. Migraine & trigeminal neuralgia. Inj: Status epilepticus; seizures in neurosurgery.
Dosage
Adults: ORAL: 100 mg two or four times before meals with max total of 600 mg daily. Titrate: Every 7-10 days. May give once daily if controlled on 300 mg/day. INJECTION: By slow IV injection or infusion (with blood pressure and ECG monitoring). Status epilepticus: 18 mg/kg at a rate not exceeding 50 mg per min, as a loading dose; maintenance doses of about 100 mg should be given thereafter at intervals of every 6-8 hr, monitored by measurement of plasma concentrations; rate and dose reduced according to weight. Children: Tonic-clonic seizures, focal seizures: IV INJECTION (over 20-30 minutes) or ORAL: Neonate, initial loading dose by slow IV injection (section 4.8.2) 18 mg/kg then by mouth 2.5-5 mg/kg twice daily adjusted according to response and plasma-phenytoin concentration (usual max 7.5 mg/kg twice daily). 1 mth-12 yr, Oral initially 1.5-2.5 mg/kg twice daily, then adjusted…
Administration
Administered by direct IV injection into a large vein. The rate of IV injection should not exceed 50 mg/min in adults or 1-3 mg/kg/min in neonates. Following IV injection, NaCl 0.9% should be injected through the same needle or catheter to reduce irritation. Compatibility: Stable in dextrose 5%, NaCl 0.9%, fat emulsion 10% IV. Stability: Phenytoin is stable as long as it remains free of haziness and precipitation. If refrigerated or frozen, a precipitate may form, but it dissolves on standing at room temperature.
Adverse Effects
Gastric distress, sleeplessness, unsteadiness. Allergic reactions. Gingival hypertrophy, hirsutism and motor activity in young patients. Blood dyscrasias, lymphadenopathy and nystagmus. Withdraw if skin rash occurs. IV injection may cause cardiovascular and CNS depression (particularly if injection too rapid) with arrhythmias, hypotension and cardiovascular collapse; alterations in respiratory function (including respiratory arrest); injection site reactions, ataxia, slurred speech, confusion, decreased coordination, paraesthesia, drowsiness, dizziness, hypersensitivity reactions, dysgeusia, headache, insomnia, nervousness, motor twitching, toxic hepatitis, liver damage, polyarthropathy, interstitial nephritis, pneumonitis, dyskinesia, cerebellar atrophy, coarsening of facial features, hypertrichosis, Peyronie's disease, Dupuytren's contracture, hyperglycaemia, respiratory arrest,…
Risk Factor (Pregnancy/Lactation)
Pregnancy: Positive evidence of risk: Use only when no safer alternative exists for a serious problem. Lactation: Contraindicated or not recommended. Contraindications: Inj: Sinus bradycardia, sino-atrial block and second- and third-degree heart block; Stokes-Adams syndrome; acute porphyria. Precautions: Severe myocardial insufficiency, hypotension. Monitor ECG and BP. Hepatic or renal impairment, diabetes, porphyria. Monitor patients for mood changes or suicidal thoughts. Risk of serious skin reactions. Monitor if lymphadenopathy develops. Elderly.
Interactions
Coumarin anticoagulants, doxycycline, isoniazid, chloramphenicol, oral contraceptives, alcohol, antifungal, antineoplastics, benzodiazepines, corticosteroids, furosemide, oestrogen, vit D, folic acid, theophylline, disulfiram, other anticonvulsants, ulcer healing drugs, antibacterials, analgesics, antacids, antipsychotics, antidepressants, St john's wort, calcium channel blockers, statins, methylphenidate, methadone, neuromuscular blocking agents, praziquantel, albendazole, antiarrhythmics, insulin, hypoglycaemics, diazoxide, antiretrovirals, immunosuppressants, anaesthetics.
Advice to Patient
Take with meals. Do not chew, crush or open capsules, swallow whole. Shake suspension well before use. Do not take antacids or calcium products within 2 hours of taking medication. Do not administer nasogastric or enteral feed to patients 2 hours before or after a dose. Do not change feed timings. Contact prescriber if there is change in mental status, unrelieved nausea, vomiting or constipation, speech impairment, chest pain, palpitations, irregular heartbeat, change in gait, swelling in glands, swollen/sore/bleeding gums, skin rash, acute fatigue, change in vision, unusual bruising or bleeding. Avoid alcohol during therapy. Maintain good oral hygiene and dental care. If you have diabetes, check your blood glucose level regularly and inform prescriber about changes. Carry identification card mentioning your medical condition and names of all medications you take. On start of therapy or…
Pharmacokinetics
Onset of action: IV: Approx. 0.5-1 hr. Absorption: Oral: Slow, variable; dependent on product formulation; decreased in neonates. Metabolism: Major metabolite (via oxidation) HPPA undergoes enterohepatic recycling. Bioavailability: Formulation dependent. Half-life elimination: Range: 7-42 hrs; Newborns (PNA <7 days): Apparent half-life greatly prolonged (clearance decreased) and then rapidly accelerates to infant levels by 5 wks of life. Time to peak, serum: (Formulation dependent): Oral: Extended-release cap: 4-12 hrs; Immediate release preparation: 1.5-3 hrs. Excretion: Urine (<5% as unchanged drug); as glucuronides.
Brands with this active ingredient
Compiled by Healify Pharmacy from published drug references. How we compile it →
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