**Core Concept**
The question tests the understanding of drug interactions, specifically between antiretroviral therapy and other medications that may exacerbate hematologic side effects. **Zidovudine**, an antiretroviral drug, is known to cause bone marrow suppression, leading to anemia and neutropenia.

**Why the Correct Answer is Right**
Given that **zidovudine** can cause bone marrow suppression, a drug that also affects the bone marrow or has similar side effects would likely exacerbate these conditions. **Ganciclovir**, an antiviral medication, is known to cause neutropenia as a side effect, making it a likely candidate to worsen anemia and neutropenia when co-administered with zidovudine.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific drug listed, it's impossible to assess its potential for additive toxicity.
**Option B:** Similarly, without the specific drug, its side effect profile cannot be considered.
**Option D:** This option is also unspecified, making it impossible to evaluate its potential for causing additive anemia and neutropenia.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that patients on **zidovudine** or other bone marrow suppressants require careful monitoring and selection of co-prescribed medications to avoid exacerbating hematologic side effects.

**Correct Answer:** D. Ganciclovir.