Which is the most common adverse effect of phenytoin in long-term therapy?

Explanation

## Most Common Adverse Effect of Phenytoin **Key Point:** Gingival hyperplasia is the most frequent chronic adverse effect of phenytoin, occurring in 20–50% of patients on long-term therapy. ### Mechanism of Gingival Hyperplasia 1. Phenytoin stimulates fibroblast proliferation in gingival tissue 2. Increased collagen deposition and connective tissue overgrowth 3. Effect is dose-dependent and reversible upon drug discontinuation 4. More pronounced in patients with poor oral hygiene ### Clinical Features - **Onset:** Usually appears 2–3 months after initiation - **Appearance:** Painless, firm, nodular enlargement of gingival margins - **Distribution:** Typically anterior gingiva (labial surface) - **Severity:** Ranges from mild to severe enough to interfere with mastication ### Management - Meticulous oral hygiene (primary prevention) - Regular dental follow-up - Scaling and polishing - Surgical gingivectomy if severe - Switch to alternative antiepileptic (e.g., levetiracetam, valproate) if unmanageable **High-Yield:** While hepatotoxicity and aplastic anemia are serious, they are rare idiosyncratic reactions. Stevens-Johnson syndrome is a severe but uncommon hypersensitivity reaction. Gingival hyperplasia is the most *common* chronic side effect that most patients on phenytoin will encounter. **Clinical Pearl:** Gingival hyperplasia is cosmetically and functionally bothersome, making it a major reason for non-adherence in young patients. Always counsel patients about oral hygiene before starting phenytoin. ### Comparison of Phenytoin Adverse Effects | Adverse Effect | Frequency | Type | Reversibility | | --- | --- | --- | --- | | Gingival hyperplasia | 20–50% | Chronic | Reversible | | Hirsutism | 20–30% | Chronic | Reversible | | Coarsening of facial features | 10–20% | Chronic | Partially reversible | | Hepatotoxicity | < 1% | Idiosyncratic | Variable | | Aplastic anemia | < 0.01% | Idiosyncratic | Often irreversible | | Stevens-Johnson syndrome | < 0.1% | Hypersensitivity | Reversible | [cite:KD Tripathi 8e Ch 11]