Question

An HIV patient is on treatment with didanosine, stavudine, and indinavir. He is diagnosed to have pulmonary tuberculosis. Which one of the following ATT drugs is to be avoided?

• A. INH
• B. Rifampin
• C. PZA
• D. Ethambutol

Hint:

Rifampin strongly induces liver enzymes that break down protease inhibitors.

Answer 1

The Correct Option is B

This question is about a drug interaction between anti-TB therapy and antiretroviral therapy (ART) in an HIV positive patient who is already taking a protease inhibitor.

1. INH: A mild liver enzyme inhibitor, generally compatible with protease inhibitor based ART, so it can be continued.
2. Rifampin: A powerful inducer of the CYP3A4 liver enzyme system. Indinavir, a protease inhibitor, is cleared through this same pathway, so rifampin speeds up its clearance and can drop indinavir levels by a large amount, enough to make the HIV treatment fail and encourage drug resistance.
3. PZA: Does not meaningfully induce the liver enzymes that affect protease inhibitors, so it is safe to continue.
4. Ethambutol: Also has no major enzyme induction effect and can be continued alongside indinavir.

The drug that must be avoided, or replaced with a weaker inducer like rifabutin, is rifampin, because of its strong effect on lowering indinavir blood levels.

Let's summarize:

• Indinavir is cleared through CYP3A4.
• Rifampin strongly induces CYP3A4 and drops indinavir levels sharply.
• INH, PZA, and ethambutol do not share this strong interaction and can be continued.

So the ATT drug to avoid here is rifampin.