Which drug is commonly used for TB exposure to prevent disease in someone who has been exposed but is not yet symptomatic?

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

Answer: (A)

The key idea is preventing progression from latent TB infection to active disease in someone who has been exposed but has no symptoms. Isoniazid is the standard first-line drug used for this purpose. When given for several months (commonly around 6–9 months), it effectively eliminates dormant TB bacteria and lowers the risk that exposure will lead to active TB. Clinicians also monitor for potential hepatotoxicity and often provide pyridoxine (vitamin B6) to prevent neuropathy.

Rifampin can be used as an alternative in some LTBI regimens, but the longtime, conventional choice for post-exposure prophylaxis in asymptomatic individuals is isoniazid. Ethambutol and pyrazinamide are mainly used as parts of treatment for active TB and are not standard prophylaxis for someone who is exposed but not yet symptomatic.