Latent tuberculosis infection — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsLatent tuberculosis infectionUSMLE Step 3

A 31-year-old has LTBI after household exposure to an isolate resistant to isoniazid but susceptible to rifampin. Active tuberculosis has been excluded, HIV testing is negative, and there are no rifamycin drug interactions. Which regimen best addresses the susceptibility result?

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Correct answer: E — Use daily rifampin for 4 months

The best answer is “Use daily rifampin for 4 months”. Four months of rifampin is a complete recommended regimen that avoids the drug to which the source isolate is resistant. Rifabutin is a substitution strategy when rifampin interactions preclude rifampin and isoniazid cannot be used; no such interaction exists here. The rifapentine and combination regimens either retain isoniazid or are not validated monotherapy schedules. CDC preferentially recommends short-course rifamycin-based LTBI regimens; four months of daily rifampin is useful when the presumed infecting strain is resistant to isoniazid but susceptible to rifampin. Rifabutin substitutes for rifampin when rifampin drug interactions preclude its use and isoniazid cannot be used. The alternatives use a different threshold, timing, population, or intervention and therefore do not match the clinical facts presented.

Reference: CDC: Treatment for Latent Tuberculosis Infection: https://www.cdc.gov/tb/hcp/treatment/latent-tuberculosis-infection.html