Phenytoin

Antiepileptic (Na⁺ Channel Blocker)

Drug Class: Antiepileptic (Na⁺ Channel Blocker)
Mechanism of Action (MOA): Stabilizes inactivated voltage-gated Na⁺ channels → ↓ repetitive neuronal firing.
Black Box Warning: IV use — cardiovascular risk with rapid infusion: do not exceed 50 mg/min (adults); too-rapid IV can cause severe hypotension and cardiac arrhythmia (also applies to fosphenytoin).
Clinical Notes: Focal/tonic-clonic seizures and status. Zero-order kinetics (narrow window); gingival hyperplasia, hirsutism, nystagmus/ataxia, SJS (HLA-B*1502).
Source: FDA label