Phenytoin

Phenytoin

1. Drug at a glance & historical perspective

• Phenytoin = 5,5-diphenylhydantoin — a five-membered hydantoin ring with two phenyl substituents on the C5 carbon; structurally similar to barbiturates but with a 5-member (not 6-member) ring (Katzung 16e Ch-24, pp.435-9; G&G 14e Ch-20, pp.391-2).
• Synthesised in 1908 as a barbiturate analogue but shelved due to poor sedative property; its anticonvulsant activity was specifically discovered in 1938 by Merritt and Putnam using the newly-developed maximal-electroshock seizure model — a landmark in rational anticonvulsant screening (KDT 8e Ch-30, p.440; G&G 14e Ch-20, p.391).
• Pharmacologically pivotal because it was the first non-sedating anticonvulsant — it abolishes the tonic phase of maximal-electroshock seizures without general CNS depression at therapeutic doses (KDT 8e Ch-30, p.440).
• Still in the WHO Model List of Essential Medicines despite being the oldest non-sedating AED still in routine clinical use; in the modern era it has been displaced as a chronic first-line agent by carbamazepine, valproate, lamotrigine, and levetiracetam owing to its ADR burden and interaction profile — but it remains indispensable for status epilepticus and is widely used in low-resource settings (Katzung 16e Ch-24, p.444; G&G 14e Ch-20, p.391).
• For the Indian context, phenytoin (Eptoin, Dilantin, Epsolin, Fentoin-ER) remains widely prescribed: 100 mg cap ≈ ₹2; oral suspension and IV formulations are routinely stocked (KDT 8e Ch-30, p.441).