## Common Causative Drugs in SJS/TEN **Key Point:** Sulfonamides, particularly **trimethoprim-sulfamethoxazole (TMP-SMX)**, are the leading cause of SJS/TEN globally and in India. ### Drug Risk Hierarchy for SJS/TEN | Drug Class | Relative Risk | Notes | |---|---|---| | **Sulfonamides** | **Highest** | TMP-SMX most frequent; risk ~1 per 1,000–3,000 exposures | | **Anticonvulsants** | High | Phenytoin, carbamazepine, phenobarbital | | **Antiretrovirals** | High | Nevirapine (esp. in women with CD4 >250), abacavir | | **NSAIDs** | Moderate | Ibuprofen, naproxen; lower absolute risk than sulfonamides | | **Beta-lactams** | Low–Moderate | Penicillins and cephalosporins; less common than sulfonamides | | **Allopurinol** | Moderate | Especially in renal impairment | ### Why Sulfonamides? **High-Yield:** Sulfonamides are metabolized to reactive intermediates (hydroxylamine metabolites) that form haptens and trigger strong CD8+ T-cell responses. The risk is dose-dependent and increases with prolonged exposure. **Clinical Pearl:** In India, TMP-SMX is widely used for: - Urinary tract infections - Pneumocystis prophylaxis in HIV/AIDS - Toxoplasmosis prophylaxis This widespread use translates to higher incidence of SJS/TEN from sulfonamides compared to other drugs. **Mnemonic:** **SCAR** (Severe Cutaneous Adverse Reactions) — **S**ulfonamides, **C**arbamazepine, **A**llopurinol, **R**etrovirals are the "big four" culprits. [cite:Park 26e Ch 7] 
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