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

Step 1: Understanding the Question:
This patient is on antiretroviral therapy that includes indinavir, a protease inhibitor, along with zalcitabine and lamivudine. We need to find which anti-tubercular drug is unsafe to add to this combination.

Step 2: Key Concept:
Protease inhibitors like indinavir are broken down by the liver enzyme CYP3A4. Any drug that strongly switches on (induces) this enzyme will speed up the breakdown of indinavir, drop its blood level, and risk failure of the HIV treatment along with drug resistance.

Step 3: Detailed Explanation:
Rifampin is one of the strongest known inducers of CYP3A4. Giving it with indinavir can cut the protease inhibitor's blood level so much that the antiretroviral regimen stops working properly. Because of this, rifampin is avoided in patients on protease inhibitors, and rifabutin, a much weaker enzyme inducer, is used in its place when anti-TB cover is needed.
INH is mainly cleared by liver acetylation and does not meaningfully induce CYP3A4, so it does not threaten indinavir levels.
Pyrazinamide (PZA) has no major interaction with protease inhibitors through this enzyme pathway.
Ethambutol is excreted mostly by the kidney and also does not induce CYP3A4.

Step 4: Final Answer:
Rifampin should be avoided because it drives down indinavir levels through CYP3A4 induction.