A patient suffering from AIDS is on zidovudine, lamivudine and indinavir therapy. He develops pulmonary tuberculosis for which treatment is started. Which of the following should be avoided in him?
First, I need to recall the interactions between antiretrovirals and TB medications. Zidovudine is a NRTI, lamivudine is also a NRTI, and indinavir is a protease inhibitor. The TB treatment typically includes INH, RIF, EMB, and PZA. The key here is rifampin (RIF), which is a potent inducer of hepatic enzymes. Since indinavir is metabolized by the liver, especially the CYP450 system, RIF can induce this system, leading to decreased levels of indinavir. That's a problem because lower indinavir levels can lead to treatment failure and resistance.
So, the answer is to avoid rifampin. The options might have RIF as one of the choices. Let me check the options again. The question says "which should be avoided," and if RIF is an option, that's the correct answer. The other TB drugs like INH, EMB, or PZA don't interact as significantly with protease inhibitors. Also, some guidelines recommend using rifabutin instead of RIF when on protease inhibitors because it has less enzyme induction.
Wait, but the question is about which to avoid. So the correct answer is RIF. The other options would be the other TB drugs. Let me make sure. Yes, RIF is the one that's contraindicated here because of the interaction with indinavir. The other drugs aren't a problem. So the correct answer is the option with rifampin.
**Core Concept**
This question examines drug interactions between antiretroviral therapy (ART) and tuberculosis (TB) medications. Specifically, **rifampin** (a first-line TB drug) induces hepatic CYP3A4 enzymes, reducing plasma concentrations of **protease inhibitors** like indinavir, thereby compromising HIV treatment efficacy.
**Why the Correct Answer is Right**
Rifampin is a potent inducer of the **CYP3A4 enzyme system**, which metabolizes indinavir. This induction accelerates indinavir breakdown, lowering its serum levels below therapeutic thresholds and risking HIV-1 resistance. Clinically, **rifampin should be avoided** in patients on protease inhibitors. Alternative TB drugs like **rifabutin** (a weaker inducer) are preferred to minimize this interaction.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid (INH) inhibits CYP2E1 and weakly inhibits CYP3A4; no significant interaction with indinavir.
**Option B:** Pyrazinamide (PZA) has minimal effect on CYP enzymes and is safe with protease inhibitors.
**Option C:** Ethambutol (EMB) is metabolized independently of CYP450 and does not interfere with indinavir.
**Clinical Pearl / High-Yield Fact**
**Rifampin induces CYP3A4**, reducing protease inhibitors (e.g., ind