A 32-year-old man from rural Maharashtra presents with a 3-month history of productive cough, fever, and night sweats. Chest X-ray shows cavitary lesions in the right upper lobe. Sputum smear microscopy is positive for acid-fast bacilli. He is started on standard first-line anti-tuberculous therapy (RIPE: Rifampicin, Isoniazid, Pyrazinamide, Ethambutol). After 2 weeks of treatment, he develops acute onset jaundice with ALT 320 U/L and AST 380 U/L. Total bilirubin is 4.2 mg/dL. Which drug is most likely responsible for this hepatotoxicity and should be temporarily discontinued?

Explanation

## Drug-Induced Hepatotoxicity in TB Treatment ### Clinical Scenario Analysis The patient has developed acute hepatotoxicity (elevated transaminases and hyperbilirubinemia) within 2 weeks of initiating standard first-line therapy. Among the four first-line drugs, three are hepatotoxic: Rifampicin, Isoniazid, and Pyrazinamide. ### Hepatotoxicity Profile of First-Line Agents | Drug | Hepatotoxicity Incidence | Onset | Mechanism | Severity | |------|--------------------------|-------|-----------|----------| | **Pyrazinamide** | 1–3% | 2–8 weeks | Dose-dependent; metabolite uric acid accumulation | Mild to moderate; dose-related | | Isoniazid | 0.5–2% | Variable (weeks to months) | Idiosyncratic; acetylator status-dependent | Can be severe; slow onset | | Rifampicin | <1% | Rare | Enzyme induction; usually mild | Mild; rarely clinically significant | | Ethambutol | <0.5% | Rare | Minimal hepatotoxicity | Negligible | **Key Point:** Pyrazinamide is the most common cause of hepatotoxicity in the first 2–8 weeks of TB treatment, with a dose-dependent mechanism. ### Why Pyrazinamide? 1. **Timing**: Hepatotoxicity typically appears 2–8 weeks into therapy — this patient is at 2 weeks, the earliest window. 2. **Dose-dependent**: Pyrazinamide's hepatotoxicity is directly related to drug accumulation and dose; it is the most predictable hepatotoxin among first-line drugs. 3. **Mechanism**: Pyrazinamide is metabolized to uric acid, which can cause both hepatotoxicity and hyperuricemia. 4. **Incidence**: 1–3% of patients develop clinically significant hepatotoxicity, the highest among first-line agents. ### Management Algorithm ```mermaid flowchart TD A["Acute hepatotoxicity on TB therapy"]:::outcome --> B{"Transaminases > 3× ULN?"}:::decision B -->|Yes| C["Stop all hepatotoxic drugs"]:::action C --> D["Identify culprit drug"]:::action D --> E{"Timeline & pattern?"}:::decision E -->|"Early onset 2–8 weeks"| F["Likely Pyrazinamide"]:::outcome E -->|"Delayed or idiosyncratic"| G["Likely Isoniazid"]:::outcome F --> H["Restart therapy without PZA"]:::action G --> I["Restart therapy without INH"]:::action H --> J["Rechallenge PZA after LFTs normalize"]:::action ``` **Clinical Pearl:** If pyrazinamide must be reintroduced, do so cautiously after liver function normalizes; some patients tolerate lower doses or intermittent dosing. **High-Yield:** Pyrazinamide is the single most common cause of hepatotoxicity in the intensive phase of TB treatment. Always monitor LFTs at baseline and weeks 2, 4, and 8. **Mnemonic:** **RIPE-H** (Rifampicin, Isoniazid, Pyrazinamide, Ethambutol, Hepatotoxicity) — remember **P** for **Pyrazinamide = Primary hepatotoxin early on**.