Which antiepileptic drug acts primarily by blocking voltage-gated sodium channels and is known to cause gingival hyperplasia as a chronic side effect?

Explanation

## Phenytoin: Mechanism and Side Effects **Key Point:** Phenytoin is a first-generation antiepileptic that stabilizes neuronal membranes by blocking voltage-gated sodium channels, preventing repetitive firing of action potentials. ### Mechanism of Action Phenytoin binds to the inactive state of Na⁺ channels and prolongs their inactivation, reducing neuronal excitability. This is particularly effective for tonic-clonic seizures and focal seizures. ### Gingival Hyperplasia Gingival hyperplasia occurs in 20–30% of patients on chronic phenytoin therapy. This is a dose-dependent, reversible side effect that results from: - Increased collagen synthesis in gingival fibroblasts - Impaired collagen degradation - Enhanced response to plaque and inflammation **Clinical Pearl:** Good oral hygiene can reduce the severity of gingival hyperplasia, but the condition often necessitates switching to an alternative antiepileptic if cosmetically or functionally problematic. ### Other Notable Phenytoin Side Effects - Hirsutism (hypertrichosis) - Coarse facial features - Osteomalacia (chronic use) - Fetal hydantoin syndrome (teratogenic in pregnancy) - Hepatotoxicity (rare) - Drug interactions (induces CYP450 enzymes) **High-Yield:** Phenytoin is a classic cause of gingival hyperplasia in medical education — this association is frequently tested in NEET PG.