## **Core Concept**
Zidovudine, also known as AZT (azidothymidine), is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of HIV/AIDS. It works by inhibiting the reverse transcriptase enzyme, which is essential for the replication of the HIV virus. However, like all medications, zidovudine can cause side effects.

## **Why the Correct Answer is Right**
The correct answer, **Bone marrow suppression**, is a well-known side effect of zidovudine. This suppression can lead to **anemia** and **neutropenia** (a decrease in white blood cells), which are significant concerns in patients with AIDS, as they can increase the risk of infections and anemia-related complications. The mechanism involves the drug's interference with the mitochondrial DNA synthesis in bone marrow cells, leading to their suppression.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While gastrointestinal disturbances are common side effects of many drugs, they are not the most notable or specific side effect associated with zidovudine compared to bone marrow suppression.
- **Option B:** Hepatotoxicity can occur with some antiretroviral drugs but is more commonly associated with other classes of antiretroviral medications, not specifically highlighting zidovudine's primary concern.
- **Option C:** Nephrotoxicity is a side effect seen with certain antiretroviral drugs, particularly tenofovir, another NRTI, but not primarily with zidovudine.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **bone marrow suppression** due to zidovudine often necessitates dose adjustment or temporary cessation of the drug, and **monitoring of blood counts** is a crucial part of managing patients on this medication. This side effect highlights the importance of regular laboratory monitoring in patients on antiretroviral therapy.

## **Correct Answer:** D. Bone marrow suppression