A known sputum positive pulmonary tuberculosis patient currently on INH, rifampicin, pyrizinamide and ethambutol is found to be HIV positive. His CD4 count is 100 /dl and viral load is more than 50,000 copies/ml. Which of the following antiretroviral drug should be avoided in this patient?

**Core Concept**
Pulmonary tuberculosis (TB) and HIV co-infection requires careful management of antiretroviral therapy (ART) to avoid interactions and adverse effects. The patient's low CD4 count and high viral load indicate a need for ART, but certain antiretroviral drugs can exacerbate TB or interact with TB medications.

**Why the Correct Answer is Right**
The patient is on rifampicin, which is a potent inducer of the cytochrome P450 enzyme system. Rifampicin can decrease the plasma concentrations of many antiretroviral drugs, including protease inhibitors and non-nucleoside reverse transcriptase inhibitors (NNRTIs). However, rifampicin has a particularly significant interaction with the protease inhibitor saquinavir, which is metabolized by the CYP3A4 enzyme. Rifampicin can increase the metabolism of saquinavir, leading to decreased plasma concentrations and reduced efficacy.

**Why Each Wrong Option is Incorrect**
**Option A:** Nevirapine is an NNRTI that does not require dose adjustment with rifampicin. It is a safe choice in this patient.
**Option B:** Efavirenz is another NNRTI that is not significantly affected by rifampicin. It can be used in patients taking rifampicin.
**Option C:** Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) that does not interact with rifampicin. It is a safe choice in this patient.
**Option D:** Stavudine is another NRTI that does not interact with rifampicin. It can be used in patients taking rifampicin.

**Clinical Pearl / High-Yield Fact**
When managing HIV-TB co-infection, it's essential to monitor the plasma concentrations of antiretroviral drugs and adjust doses as needed to avoid decreased efficacy or toxicity.

**Correct Answer:** C. Stavudine

✓ Correct Answer: C. Ritonavir