Phenytoin

Introduction

• Phenytoin — 5,5-diphenylhydantoin — a five-membered hydantoin ring with two phenyl groups on C5; a barbiturate analogue but with a 5-membered (not 6-membered) ring.
• Historical landmark — anticonvulsant activity discovered by Merritt & Putnam in 1938 using the maximal-electroshock seizure model — the first non-sedating anticonvulsant, abolishing the tonic phase of MES without general CNS depression.
• Current place — the oldest non-sedating AED still in routine use; displaced as chronic first-line by carbamazepine, valproate, lamotrigine and levetiracetam (ADR + interaction burden) but remains indispensable for status epilepticus and in low-resource settings.
• Indian context — Eptoin, Dilantin, Epsolin, Fentoin-ER — widely prescribed; 100 mg capsule ≈ ₹2; oral suspension and IV forms routinely stocked; retained in WHO mhGAP core AEDs for LMICs.