## Drug-Induced SJS/TEN: Causative Agents **Key Point:** Sulfonamides, particularly TMP-SMX, are the single most common drug trigger for SJS/TEN globally and in India, accounting for 25–30% of drug-induced cases. ### High-Risk Drug Classes and Relative Frequency | Drug Class | Relative Risk | Examples | Frequency in SJS/TEN | |------------|---------------|----------|---------------------| | **Sulfonamides** | Highest | TMP-SMX, sulfadiazine | 25–30% | | Aromatic anticonvulsants | High | Phenytoin, carbamazepine, phenobarbital | 15–20% | | NSAIDs | Moderate–High | Naproxen, ibuprofen, piroxicam | 10–15% | | Allopurinol | Moderate | Especially in renal impairment | 5–10% | | Antibiotics (non-sulfa) | Moderate | Fluoroquinolones, macrolides, beta-lactams | 10–15% | **High-Yield:** In India, TMP-SMX remains the leading cause because of its widespread use in treating urinary tract infections, pneumocystis prophylaxis in HIV, and bacterial infections. The risk is highest in the first 2–8 weeks of exposure. **Clinical Pearl:** Patients with HIV/AIDS on TMP-SMX prophylaxis have a 100–1000-fold increased risk of SJS/TEN compared to the general population. **Mnemonic:** **SCAR Drugs** (Severe Cutaneous Adverse Reactions) — **S**ulfonamides, **C**arbamazepine, **A**llopurinol, **R**etinoids (and aromatic anticonvulsants). [cite:Harrison 21e Ch 56] 
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