Which antiretroviral inhibits HIV entry by preventing fusion of the viral envelope with the host cell membrane?

• A. Zidovudine
• B. Enfuvirtide
• C. Efavirenz
• D. Lamivudine

Answer: (B)

Blocking HIV entry by preventing fusion of the viral envelope with the host cell membrane is achieved by fusion inhibitors. Enfuvirtide is a fusion inhibitor that binds the gp41 subunit of the HIV envelope glycoprotein, preventing the conformational changes needed for the viral and cellular membranes to fuse. This stops the virus from entering the cell. It’s given by subcutaneous injection and is often used in patients with resistant HIV strains. Other drugs listed work at different steps: zidovudine and lamivudine are nucleoside reverse transcriptase inhibitors that block reverse transcription, and efavirenz is a non-nucleoside reverse transcriptase inhibitor; neither prevents viral entry or fusion.