A 35-year-old patient with smear-positive pulmonary TB is started on first-line treatment. After 2 months, sputum culture remains positive. DST reveals resistance to isoniazid (INH) and rifampicin but sensitivity to fluoroquinolones and injectable agents. Which drug resistance pattern is this?
- A Multidrug-resistant TB (MDR-TB) — requires at least 18 months of second-line therapy ✓
- B Pre-XDR TB — requires third-line agents including bedaquiline and delamanid
- C Extensively drug-resistant TB (XDR-TB) — requires >24 months of treatment with novel agents
- D Rifampicin-resistant TB (RR-TB) — can be treated with isoniazid-containing regimens
Explanation
Multidrug-resistant TB (MDR-TB) is defined as resistance to at least isoniazid AND rifampicin (the two most important first-line drugs). This case shows INH+rifampicin resistance with preserved fluoroquinolone and injectable sensitivity, which is MDR-TB (not XDR). Pre-XDR TB (WHO 2021 revised definition) is MDR-TB resistant to any fluoroquinolone, while XDR-TB is MDR-TB + resistance to any fluoroquinolone + at least one of bedaquiline/linezolid. MDR-TB treatment per NTEP in India uses the Bedaquiline-containing shorter or longer regimen (6BPaLM or 18–20 months) with outcomes monitored by culture conversion. Pyrazinamide, ethambutol, ethionamide, PAS, and cycloserine are adjunct options based on DST.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.