Phenytoin

A classic antiepileptic drug used to control seizures and prevent status epilepticus.

What is Phenytoin?

Phenytoin is an antiepileptic (anticonvulsant) medication used to control tonic–clonic and partial seizures.

It stabilizes neuronal membranes and prevents abnormal electrical activity in the brain.

History & Background

Phenytoin was introduced in the 1930s and marked a major breakthrough in epilepsy treatment due to its effectiveness without excessive sedation.

Chemical Structure & Properties

• IUPAC name: 5,5-diphenylimidazolidine-2,4-dione
• Molecular formula: C₁₅H₁₂N₂O₂
• Molar mass: 252.27 g/mol
• Functional groups: Hydantoin ring, aromatic rings

Mechanism of Action

Phenytoin prevents seizures by:

• Blocking voltage-gated sodium channels
• Reducing repetitive neuronal firing
• Stabilizing neuronal membranes

Pharmacokinetics

• Absorption: Variable oral absorption
• Peak plasma time: 3–12 hours
• Half-life: ~22 hours (dose-dependent)
• Metabolism: Liver (CYP2C9, CYP2C19)
• Excretion: Urine

Medical Uses

• Tonic–clonic seizures
• Partial seizures
• Status epilepticus (prevention)
• Seizure prophylaxis after neurosurgery

Dosage Guidelines

Adults: 300–400 mg/day in divided doses

Therapeutic level: 10–20 µg/mL

⚠️ Blood level monitoring is essential.

Side Effects

• Gingival hyperplasia
• Ataxia
• Nystagmus
• Hirsutism

Warnings & Precautions

• Narrow therapeutic index
• Avoid abrupt discontinuation
• Teratogenic risk

Drug Interactions

• Oral contraceptives
• Warfarin
• Alcohol

Frequently Asked Questions

Is phenytoin for epilepsy? – Yes.

Does it require blood monitoring? – Yes.

Can it be used long-term? – Yes, under supervision.

Is it sedating? – Minimal sedation.

⚠️ Educational content only. Not a substitute for professional medical advice.