What is the standard initial four-drug regimen for drug-susceptible pulmonary TB and its typical duration?

• A. Isoniazid, rifampin, pyrazinamide, ethambutol for 2 months, followed by isoniazid and rifampin for 4 additional months (total 6 months).
• B. Isoniazid, rifampin for 9 months.
• C. Ethambutol and pyrazinamide only for 6 months.
• D. Rifampin and ethambutol for 2 months then STOP.

Answer: (A)

The main idea is that drug-susceptible pulmonary TB is treated with a four-drug intensive phase to rapidly kill bacteria and prevent resistance, followed by a two-drug continuation phase to finish therapy. The standard plan uses isoniazid, rifampin, pyrazinamide, and ethambutol for two months, then continues with isoniazid and rifampin for four additional months, for a total of six months.

Pyrazinamide helps shorten treatment by sterilizing bacilli that are active but in a dormant state, while ethambutol provides coverage against potential resistance until full drug susceptibility is confirmed. Isoniazid and rifampin are the core, most potent drugs for active TB, and continuing them together after the initial phase completes the regimen once susceptibility is established, resulting in a high cure rate with good adherence.

The other options omit essential components or extend therapy inappropriately for drug-susceptible TB. For example, using only two drugs or stopping early would risk ongoing infection and development of resistance, while leaving out a key drug like pyrazinamide or ethambutol misses parts of the standard initial phase that help ensure effectiveness.