For a family member of someone with active TB, how long is isoniazid typically taken to help prevent TB?

• A. 2 weeks
• B. 6 to 12 months
• C. 2-3 years
• D. Lifelong

Answer: (B)

Preventing progression from latent TB infection to active disease requires sustained therapy to eradicate dormant bacteria. Isoniazid given to a family member of someone with active TB is typically taken for six to twelve months because this duration provides enough time to kill the latent bacilli and significantly reduce the risk of developing active TB, especially when adherence is good. Short courses of only a couple of weeks aren’t enough to prevent activation, while extending therapy to years or lifelong isn’t necessary for most exposed individuals and increases the risk of drug toxicity and adherence challenges. Six to twelve months strikes the right balance between effectiveness and safety.