What is the standard initial intensive phase of therapy for drug-susceptible tuberculosis?

• A. 6 months of therapy with INH and rifampin only
• B. 2 months of RIPE (rifampin, isoniazid, pyrazinamide, ethambutol)
• C. 4 months of therapy with RIPE
• D. 3 months of INH, rifampin, ethambutol

Answer: (B)

The main idea is that initial treatment for drug-susceptible tuberculosis uses a four-drug intensive phase to rapidly kill bacilli and prevent resistance. This intensive phase lasts two months and combines rifampin, isoniazid, pyrazinamide, and ethambutol. Pyrazinamide is particularly valuable because it targets semi-dormant bacilli in acidic environments, allowing the total duration of therapy to be shorter. Ethambutol serves as a safeguard during the early period when susceptibility is being confirmed.

After this two-month intensive phase, therapy continues with just isoniazid and rifampin for an additional four months, making the total course six months.

Why the other options aren’t correct: using six months of therapy with only INH and rifampin leaves out pyrazinamide and ethambutol and misses the crucial initial four-drug phase. A four-month regimen with RIPE omits the two-month intensive start, which is needed to rapidly reduce bacterial load and prevent resistance. A three-month course with INH, rifampin, and ethambutol excludes pyrazinamide and uses an incorrect duration, so it wouldn’t provide the proven initial intensiv phase or the standard total treatment length.