What term describes TB resistance to at least isoniazid and rifampin?

• A. Extensively drug-resistant TB
• B. Pan-drug-resistant TB
• C. Multidrug-resistant TB
• D. Mono-resistant TB

Answer: (C)

Multidrug-resistant TB refers to TB that is resistant to at least the two most potent first-line drugs, isoniazid and rifampin. This is the best label because losing both of these key drugs means standard therapy won’t work, requiring longer, more toxic, and more expensive regimens with second-line medications. Other forms—extensively drug-resistant TB (which adds resistance to fluoroquinolones and a second-line injectable), pan-drug-resistant TB (resistant to nearly all anti-TB drugs), and mono-resistant TB (resistant to only one drug)—are more extensive or narrower patterns of resistance, but the definition focused on resistance to both isoniazid and rifampin is what identifies multidrug-resistant TB.