Question

What drug should be avoided in the case of an HIV patient who is receiving zalcitabine, indinavir and lamivudine?

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

Hint:

Think about which anti-TB drug strongly induces the liver enzyme that breaks down protease inhibitors.

Answer 1

The Correct Option is B

Indinavir, one of this patient's HIV drugs, is a protease inhibitor broken down by the liver enzyme CYP3A4. Any drug that strongly revs up this enzyme will lower indinavir's blood level. Let's check each option.

1. INH: Cleared mainly by acetylation in the liver and does not meaningfully switch on CYP3A4, so it is safe with indinavir.
2. Rifampin: A powerful CYP3A4 inducer. It speeds up the breakdown of indinavir so much that blood levels can fall below the amount needed to keep the virus suppressed, risking treatment failure and resistance.
3. PZA: Does not act on CYP3A4 in a way that harms protease inhibitor levels.
4. Ethambutol: Leaves the body mainly through the kidney and does not induce CYP3A4 either.

Because rifampin can silently sink indinavir's blood level, it is the drug to avoid, with rifabutin used instead when TB treatment is unavoidable.

Let's summarize:

• Protease inhibitors depend on stable CYP3A4 activity to stay effective.
• Rifampin's strong enzyme induction drops indinavir levels and threatens HIV control.

The drug to avoid here is rifampin.