Which drug is used for TB exposure prophylaxis?

• A. Rifampin
• B. Ethambutol
• C. Isoniazid
• D. Pyrazinamide

Answer: (C)

Exposure prophylaxis aims to stop a latent infection from progressing to active tuberculosis. Isoniazid is used for this purpose because it effectively prevents the growth of Mycobacterium tuberculosis once a person has been exposed and may harbor latent bacteria. It is activated by the bacterial enzyme KatG and then inhibits mycolic acid synthesis, which disrupts the cell wall of the bacteria. Giving isoniazid for several months (often 6–9 months) greatly reduces the chance that latent infection will become active TB. It’s common to add pyridoxine (vitamin B6) to prevent peripheral neuropathy.

The other drugs listed have different primary roles: ethambutol and pyrazinamide are components of active TB treatment regimens, not standard prophylaxis. Rifampin can be used in some prevention strategies or as an alternative in specific situations, but the classic and most widely taught agent for TB exposure prophylaxis is isoniazid.