A 42-year-old woman with newly diagnosed pulmonary tuberculosis is started on standard first-line anti-tuberculous therapy. During the intensive phase, which is the most common adverse effect of the anti-TB drug regimen?

Explanation

## Most Common Adverse Effect of First-Line Anti-TB Drugs **Key Point:** Hepatotoxicity is the most common and most serious adverse effect of standard first-line anti-tuberculous therapy, occurring in 2–28% of patients depending on the definition and population studied. ### First-Line Anti-TB Drugs and Hepatotoxicity | Drug | Hepatotoxic | Mechanism | Frequency | | --- | --- | --- | --- | | Isoniazid (INH) | Yes | Metabolite-induced hepatocyte injury | Common | | Rifampicin (RIF) | Yes | Enzyme induction; direct hepatotoxicity | Common | | Pyrazinamide (PZA) | Yes | Hyperuricemia → gout; hepatitis | Common | | Ethambutol (EMB) | No | — | — | | Streptomycin (SM) | No | — | — | **High-Yield:** The three most hepatotoxic first-line drugs are **INH, RIF, and PZA**. When all three are given together (as in the intensive phase), the risk of drug-induced liver injury (DILI) is significantly increased. ### Risk Factors for Anti-TB Hepatotoxicity - Pre-existing liver disease (cirrhosis, chronic hepatitis) - Alcohol abuse - Malnutrition - Concurrent use of other hepatotoxic drugs - Age >50 years - Female gender - Slow acetylator phenotype (for INH) **Clinical Pearl:** Baseline liver function tests (LFTs) and regular monitoring (at weeks 2, 4, 8, and 12) are essential. If ALT rises >3× upper limit of normal (ULN) with symptoms, or >5× ULN without symptoms, anti-TB drugs should be temporarily discontinued and reintroduced cautiously. **Mnemonic:** **RIPE** = Rifampicin, Isoniazid, Pyrazinamide, Ethambutol (the four main first-line drugs). The first three are hepatotoxic; EMB is not. **Tip:** When a question asks about the "most common adverse effect," think about frequency in the general population, not severity. Hepatotoxicity is both common and serious, making it the best answer.