What is the typical duration of therapy for drug-susceptible TB in adults?

• A. 3 months
• B. 9 months
• C. 12 months
• D. 6 months (2 months intensive, 4 months continuation)

Answer: (D)

The standard treatment for drug-susceptible TB in adults lasts six months. This uses two phases: an intensive phase of two months with four first-line drugs (isoniazid, rifampin, pyrazinamide, ethambutol) to rapidly reduce the bacillary load and prevent resistance, followed by a continuation phase of four months with isoniazid and rifampin to finish eradicating remaining bacilli and prevent relapse. Pyrazinamide and ethambutol are stopped after the intensive phase once susceptibility is confirmed or the phase completes. This six-month schedule provides effective cure with a manageable treatment burden; shorter durations fall short of adequately clearing bacteria, while longer regimens don’t improve outcomes for typical drug-susceptible TB. Exceptions exist for certain forms or slow responses, but six months is the standard.