What is the recommended duration of isoniazid prophylaxis after TB exposure?

• A. 1-2 weeks
• B. 6-12 months
• C. 1-2 years
• D. 5 years

Answer: (B)

Preventing progression from latent TB infection to active disease relies on giving enough time for isoniazid to eliminate dormant bacilli and for the body to control the infection. The standard approach after exposure is a prolonged course of isoniazid, typically about 6 months, with many guidelines allowing up to 9 months, and some describing a range of 6–12 months to cover different patient factors. This makes 6–12 months the best choice because it reflects the usual duration that provides effective protection while balancing adherence and risk of side effects. Short courses like 1–2 weeks are far too brief to be effective, and much longer durations (1–2 years or 5 years) are not routinely required for most exposures and would add unnecessary burden and potential toxicity.