**Core Concept**
The question requires knowledge of the pharmacological interactions between antitubercular drugs and antiretroviral therapy for AIDS patients. Ethambutol, streptomycin, and pyrazinamide are first-line antitubercular drugs, but their use in patients with AIDS must be carefully considered due to potential pharmacokinetic and pharmacodynamic interactions.

**Why the Correct Answer is Right**
Rifampicin, a key component of antiretroviral therapy for AIDS patients, is a potent inducer of the cytochrome P450 enzyme system. This can lead to decreased levels of antiretroviral drugs such as protease inhibitors, compromising their efficacy. Conversely, rifampicin is not compatible with certain antiretroviral regimens, making it a critical choice for patients with AIDS. **Option A** is the correct answer because it highlights the importance of avoiding rifampicin in AIDS patients.

**Why Each Wrong Option is Incorrect**
**Option B:** Ethambutol is not contraindicated in AIDS patients but should be used with caution due to the risk of optic neuritis. This side effect is more common in patients with renal impairment or those taking other potentially ototoxic medications like streptomycin.
**Option C:** Streptomycin is an aminoglycoside antibiotic and has ototoxicity as a major side effect. While it should be used with caution in AIDS patients, it is not the primary concern in this context.
**Option D:** Pyrazinamide is a first-line antitubercular drug and is generally safe for use in AIDS patients. Its primary concern is hepatotoxicity, which requires careful monitoring.

**Clinical Pearl / High-Yield Fact**
When managing patients with AIDS and tuberculosis, carefully consider the potential interactions between antitubercular drugs and antiretroviral therapy. Rifampicin, a key component of antiretroviral therapy, can induce the cytochrome P450 enzyme system, leading to decreased levels of protease inhibitors and compromising their efficacy.

**✓ Correct Answer: A. Rifampicin**