A 28-year-old woman is diagnosed with drug-resistant tuberculosis (MDR-TB) confirmed by culture and drug susceptibility testing showing resistance to both isoniazid and rifampicin. She has no contraindications to fluoroquinolones. Which drug is the preferred choice for MDR-TB regimens?

Explanation

## Drug of Choice for MDR-TB **Key Point:** Fluoroquinolones, particularly **moxifloxacin** and levofloxacin, are the preferred backbone agents for MDR-TB regimens. They are bactericidal, have excellent tissue penetration, and are the most cost-effective and widely available second-line agents. ### Classification of Second-Line TB Drugs | Category | Agents | Role in MDR-TB | |----------|--------|----------------| | **Group A (Fluoroquinolones)** | Moxifloxacin, Levofloxacin | **Preferred backbone agents** — bactericidal, excellent penetration | | Group B (Injectable agents) | Amikacin, Capreomycin, Streptomycin | Used in intensive phase; ototoxic and nephrotoxic | | Group C (Other oral agents) | Linezolid, Bedaquiline, Clofazimine | Reserved for XDR-TB or intolerance to Group A/B | | Group D (Add-on agents) | PAS, Ethionamide, Prothionamide | Weak activity; used when options limited | ### MDR-TB Regimen Structure (WHO 2023) **Intensive Phase (6–20 months):** - **Moxifloxacin** (or levofloxacin) [backbone] - Injectable agent (amikacin or capreomycin) - High-dose isoniazid (if susceptible) - Ethionamide or prothionamide **Continuation Phase (4–20 months):** - **Moxifloxacin** [backbone] - Ethionamide or prothionamide **High-Yield:** Moxifloxacin is preferred over levofloxacin in MDR-TB because it has: - Faster bactericidal activity - Superior CNS penetration - Better in vitro activity against *M. tuberculosis* **Clinical Pearl:** Fluoroquinolones are the **only oral bactericidal agents** available for MDR-TB. Their inclusion reduces treatment duration from 20+ months to 18–20 months and improves cure rates to 60–75%. **Mnemonic:** **FABLE** = Fluoroquinolone, Amikacin/capreomycin, Bedaquiline, Linezolid, Ethionamide (agents used in MDR-TB when first-line drugs fail). ### Why Moxifloxacin Is Preferred 1. **Bactericidal activity:** Superior to levofloxacin in *in vitro* and clinical studies. 2. **Cost-effectiveness:** Much cheaper than bedaquiline or linezolid; accessible in resource-limited settings. 3. **Tolerability:** Fewer adverse effects than injectable agents (ototoxicity, nephrotoxicity) or linezolid (peripheral neuropathy, bone marrow suppression). 4. **Availability:** Widely available in India and globally. 5. **Penetration:** Excellent lung and CNS penetration. **Warning:** Fluoroquinolones are contraindicated in pregnancy (teratogenic) and should be avoided in patients with QT prolongation or severe hepatic disease.