What is the typical duration of isoniazid therapy for latent TB infection?

• A. 6–9 months
• B. 3 months
• C. 12 months
• D. 18 months

Answer: (A)

Treating latent TB infection with isoniazid aims to eradicate dormant bacilli and prevent reactivation, so a prolonged course is used. The usual monotherapy duration is six to nine months because this range provides effective protection while balancing safety and adherence. Six months works well for many patients, but extending to nine months offers slightly higher protection in some groups and ensures adequate treatment completion. Extending beyond nine months does not significantly improve outcomes and raises the risk of hepatotoxicity and poor adherence. Shorter regimens, such as three months, are not sufficient with isoniazid alone to reliably prevent progression of latent infection.