Generic
Phenytoin
2 brands available in the market
At a glance
Phenytoin is an antiepileptic medication used for the treatment and prevention of epilepsy (seizures). It controls seizures by decreasing the abnormal and excessive activity of nerve cells in the brain.
Description
Phenytoin is an anticonvulsant that stabilizes neuronal membranes and decreases seizure activity by increasing efflux or decreasing influx of sodium ions across cell membranes in the motor cortex during generation of nerve impulses. It acts as an antiarrhythmic by extending the effective refractory period and suppressing ventricular pacemaker automaticity.
Indications
- Epilepsy/Seizures (tonic-clonic and complex partial)
- Status epilepticus
- Antiarrhythmic
Therapeutic class
Antiepileptic drugs
Pharmacological class
Sodium Channel Blocker (Anticonvulsant)
Pharmacology
Phenytoin stabilizes neuronal membranes and decreases seizure activity by modulating sodium ion flux across cell membranes in the motor cortex. It extends the effective refractory period and suppresses ventricular pacemaker automaticity, demonstrating antiarrhythmic properties.
Mechanism of action
Reduces seizure activity by blocking sodium channels on neuronal membranes.
Dosage
Adult Dose (Oral):
- Epilepsy: Initially 3-4 mg/kg/day (single or divided doses); alternatively 150-300 mg/day, gradually increased to 600 mg/day if needed; Maintenance: 200-500 mg/day
Pediatric Dose (Oral):
- Neonates (<28 days): 5 mg/kg/day in 2 divided doses
- 6 months-16 years: 5 mg/kg/day in 2-3 divided doses
- Maintenance (age-based): 6 months-4 years: 8-10 mg/kg/day; 4-7 years: 7.5-9 mg/kg/day; 7-10 years: 7-8 mg/kg/day; 10-16 years: 6-7 mg/kg/day
Administration
- May be taken with or without food; take at a fixed time
- Swallow tablet whole; do not chew, crush or break
- Take regularly as prescribed by your doctor
Missed dose
If you miss a dose, take it as soon as you remember; skip if it's almost time for next dose; do not double the dose.
Side effects
Common Side Effects:
- Skin rash
- Headache
- Dizziness
- Vomiting
- Nausea
- Slurred speech
- Vertigo
- Confusion
- Nervousness
- Constipation
- Tremor
- Altered walking
- Gum hypertrophy
Precautions & warnings
- May affect driving ability; do not drive if drowsy or dizzy
- Do not stop suddenly (may increase seizure frequency)
- May cause gum hypertrophy; maintain oral/dental hygiene
- May increase blood sugar levels; inform doctor if taking diabetes medications
- Do not change the brand of the medicine
- Unsafe during pregnancy
Contraindications
- Pregnancy
Drug interactions
- Alcohol, sedatives: Effects potentiated
- Paracetamol, lithium: Toxic effects enhanced
- Acetazolamide: Increased risk of osteomalacia
- Allopurinol, capecitabine, cimetidine, CYP2C9/19 inhibitors, disulfiram, methylphenidate, metronidazole, omeprazole, SSRI, trazodone, trimethoprim: Increased serum concentrations
- Antiarrhythmics, anticonvulsants, antipsychotics, beta-blockers, calcium channel blockers, chloramphenicol, corticosteroids, doxycycline, estrogens, HMG-CoA reductase inhibitors, methadone, theophylline, TCAs: Increased metabolism
- Clozapine, ciclosporin, tacrolimus, digoxin, itraconazole, levodopa, thyroid hormones, topiramate: Decreased levels/effects
- Potentially fatal: Enhances hypotensive properties of dopamine and cardiac depressant properties of lidocaine
Food interactions
Alcohol consumption with Phenytoin is unsafe.
Use in pregnancy
Use in Pregnancy: Unsafe during pregnancy; definite evidence of risk to the developing baby; doctor may prescribe in life-threatening situations if benefits outweigh risks.
Pregnancy Category: D — always consult a doctor before taking during pregnancy.
Use in lactation
Use in Lactation: Safe during breastfeeding; human studies show insignificant transfer to breast milk and no harm to the baby.
Pediatric use
Pediatric dosing based on age and weight; consult your doctor.
Geriatric use
Caution required in elderly patients; dose adjustment may be needed.
Renal / hepatic impairment
Renal Impairment: Caution in kidney disease; dose adjustment may be needed; consult your doctor.
Hepatic Impairment: Caution in liver disease; dose adjustment may be needed; consult your doctor.
Overdose effects
Overdose: Nystagmus, ataxia, diplopia, nausea, vomiting, drowsiness, coma, hypotension, respiratory depression. Treatment: Supportive; gastric lavage; activated charcoal; phenytoin is not removed by dialysis.
Storage conditions
Store in a cool and dry place; keep out of reach of children.
Chemical structure
Phenytoin