**Core Concept:** Prevention of HIV transmission from an infected pregnant mother to the child is crucial in controlling the HIV epidemic. This can be achieved through the use of antiretroviral medications that suppress the virus and reduce viral load.

**Why the Correct Answer is Right:** The correct answer, AZT (azidothymidine), is a nucleoside reverse transcriptase inhibitor (NRTI) that is widely used in the prevention of mother-to-child transmission of HIV. When administered to pregnant women with HIV, AZT reduces the viral load and prevents the virus from replicating, thus reducing the risk of transmission to the child during labor and delivery.

**Why Each Wrong Option is Incorrect:**

A. AZT is not the only drug used for preventing mother-to-child transmission of HIV. Other drugs like Zidovudine, Tenofovir, and Lamivudine are also used in combination with AZT. However, AZT is the first-line option recommended by WHO.

B. AZT is not a prophylactic drug for the child. Prophylactic drugs are given to the child to prevent HIV infection, but AZT is given to the pregnant mother. Combination therapy with AZT and other antiretroviral drugs is more effective in preventing mother-to-child transmission.

C. AZT is not the only antiretroviral drug used for HIV treatment. There are other classes of antiretroviral drugs, like protease inhibitors and integrase inhibitors, that are used in combination therapy for HIV treatment. However, for preventing mother-to-child transmission, AZT is the first-line option recommended by WHO.

D. AZT is not the only drug used for preventing mother-to-child transmission of HIV during childbirth. Combination therapy with AZT and other antiretroviral drugs is more effective in preventing mother-to-child transmission.

**Clinical Pearl:** In addition to AZT, combination therapy with other antiretroviral drugs, such as lamivudine and nevirapine, is the recommended approach for preventing mother-to-child transmission of HIV. This combination therapy significantly reduces the risk of HIV transmission during childbirth, labor, and breastfeeding.

**Correct Answer:** A. AZT (azidothymidine) is a nucleoside reverse transcriptase inhibitor (NRTI) that is used as part of combination therapy to prevent mother-to-child transmission of HIV. The combination of AZT, lamivudine, and nevirapine is recommended by WHO for this purpose. AZT is administered to the pregnant mother, while lamivudine and nevirapine are given to the child. This combination therapy significantly reduces the risk of HIV transmission during childbirth, labor, and breastfeeding.