A 4-year-old girl with newly diagnosed pulmonary TB is found to have hepatic dysfunction (ALT 120 U/L, AST 140 U/L) during baseline investigations. Which drug should be AVOIDED or used with extreme caution in the first-line regimen due to hepatotoxicity risk?

Explanation

## Hepatotoxicity and Anti-TB Drug Selection **Key Point:** Pyrazinamide is the most hepatotoxic of the first-line anti-TB drugs and should be avoided or used with extreme caution in children with pre-existing hepatic dysfunction. ### Hepatotoxicity Profile of First-Line Drugs | Drug | Hepatotoxicity Risk | Mechanism | Clinical Significance | | --- | --- | --- | --- | | **Pyrazinamide** | **High (3–5%)** | Hyperuricemia; direct hepatocyte injury | **Most hepatotoxic; avoid in liver disease** | | Isoniazid | Moderate (0.5–1%) | Acetylation-dependent metabolite; slow acetylators at risk | Acceptable with monitoring | | Rifampicin | Low–Moderate (0.5–1%) | Enzyme induction; rare direct toxicity | Acceptable; induces own metabolism | | Ethambutol | Very Low (<0.1%) | Minimal hepatic metabolism | Safe in hepatic dysfunction | **High-Yield:** In a child with pre-existing hepatic dysfunction, pyrazinamide should be omitted from the regimen. The alternative regimen becomes: - **Intensive phase:** Isoniazid + Rifampicin + Ethambutol for **3 months** (instead of 2 months) - **Continuation phase:** Isoniazid + Rifampicin for **5 months** (instead of 4 months) - **Total duration:** 8 months (instead of 6 months) ### Management of Hepatic Dysfunction in TB 1. **Baseline LFTs:** Measure ALT, AST, bilirubin, albumin before starting therapy 2. **Pyrazinamide avoidance:** If ALT/AST > 3× upper limit of normal or bilirubin elevated, omit pyrazinamide 3. **Monitoring:** Repeat LFTs at 2 weeks, 1 month, and 3 months 4. **Drug-induced hepatitis:** If ALT rises >5× ULN or symptoms develop (jaundice, right upper quadrant pain), stop all drugs and investigate **Clinical Pearl:** Pyrazinamide also causes hyperuricemia and can precipitate gout in susceptible individuals — an additional reason to avoid it in high-risk patients. **Mnemonic:** **"PZA Hurts the Liver"** — Pyrazinamide is the Hepatotoxic Agent to avoid in liver disease. [cite:Park 26e Ch 12; WHO Guidelines on TB in Children 2022]