Select the drug that is active against both HIV and hepatitis B virus :
**Core Concept**
The question requires knowledge of antiviral medications that are effective against dual infections of HIV and hepatitis B virus (HBV). This involves understanding the pharmacological properties of antiretroviral and antiviral medications, as well as their mechanisms of action.
**Why the Correct Answer is Right**
Entecavir is a nucleoside analog reverse transcriptase inhibitor (NtRTI) that is active against both HIV and HBV. It works by inhibiting the replication of both viruses through the inhibition of viral DNA synthesis. Entecavir is specifically designed to target the HBV polymerase, preventing the virus from replicating. Its dual activity makes it an attractive option for patients co-infected with HIV and HBV.
**Why Each Wrong Option is Incorrect**
**Option A:** Tenofovir disoproxil fumarate (TDF) is a nucleotide reverse transcriptase inhibitor (NtRTI) that is effective against HIV, but it is not specifically indicated for the treatment of HBV. While TDF may have some activity against HBV, it is not the preferred treatment option for dual infection.
**Option B:** Lamivudine is a nucleoside analog reverse transcriptase inhibitor (NtRTI) that is effective against both HIV and HBV. However, it is not as potent as entecavir against HBV, and its use is often limited by the development of resistance.
**Option C:** Emtricitabine is a nucleoside analog reverse transcriptase inhibitor (NtRTI) that is effective against both HIV and HBV. Like lamivudine, it is not as potent as entecavir against HBV, and its use is often limited by the development of resistance.
**Clinical Pearl / High-Yield Fact**
When treating patients co-infected with HIV and HBV, it is essential to use antiviral medications that are effective against both viruses. Entecavir is a preferred option due to its potent activity against HBV and its ability to prevent the development of resistance.
**Correct Answer:** C. Emtricitabine