In drug-susceptible pulmonary TB therapy, what is the typical duration of the initial intensive phase?

• A. One month.
• B. Three months.
• C. Two months.
• D. Six months.

Answer: (C)

In drug-susceptible pulmonary TB, treatment is structured to rapidly kill actively growing bacilli and prevent the development of resistance. This is done with a four-drug intensive phase that typically lasts about two months. The standard regimen uses isoniazid, rifampin, pyrazinamide, and ethambutol during this period. Pyrazinamide and ethambutol help target bacilli in different states and prevent early resistance while susceptibility is being confirmed, while isoniazid and rifampin provide strong bactericidal activity to quickly reduce the bacterial load. After these two months, therapy usually continues with two drugs (commonly isoniazid and rifampin) for another four months, making a total of six months of treatment.

Options like one month, three months, or six months do not fit the typical initial phase: one month is too short to achieve adequate sterilization and resistance prevention, three months exceeds the standard initial window, and six months refers to the total duration rather than the intensive phase.