Which of the following anti-tubercular drug is avoided in a HIV positive patient on zidovudine, lamivudine and indinavir therapy who develops TB?
**Core Concept**
Rifampicin is a potent inducer of the cytochrome P450 enzyme system, which plays a crucial role in the metabolism of many drugs, including antiretroviral medications used in HIV therapy. This enzyme induction can lead to significant reductions in the plasma concentrations of these medications, potentially compromising their efficacy and increasing the risk of antiretroviral resistance.
**Why the Correct Answer is Right**
Rifampicin's ability to induce the cytochrome P450 system is particularly concerning when co-administered with antiretroviral medications such as zidovudine, lamivudine, and indinavir. By inducing these enzymes, rifampicin can accelerate the metabolism of these medications, resulting in decreased plasma levels and reduced antiviral efficacy. This interaction can have serious consequences, including the development of antiretroviral-resistant HIV strains and increased risk of treatment failure.
**Why Each Wrong Option is Incorrect**
**Option A:** Pyrazinamide is not known to interact significantly with antiretroviral medications, making it a safer choice for HIV-positive patients with TB.
**Option B:** Isoniazid is generally well-tolerated and does not have significant interactions with antiretroviral medications, although it may require regular monitoring for liver toxicity.
**Option C:** Ethambutol can cause optic neuritis, but it does not have significant interactions with antiretroviral medications and is not the primary concern in this scenario.
**Clinical Pearl / High-Yield Fact**
When treating HIV-positive patients with TB, it is essential to carefully consider potential drug interactions and choose antitubercular medications that minimize the risk of pharmacokinetic interactions with antiretroviral therapies. Rifampicin is a potent inducer of the cytochrome P450 system, making it a high-risk choice for patients on antiretroviral therapy.
**✓ Correct Answer:** D. Rifampicin