This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Fusion inhibitor is- 
Select and explain. 
A. Enfuvirtide, B. Ritonavir, C. Efavirenz, D. Didanosine
A: Enfuvirtide
Answer: A: Enfuvirtide 
Explanation: Ans. is 'a' i.e., Enfuvirtide New drugs in HIV infection o Etravirine is recently approved NNRTI. This is the second generation NNRTI and is effective against HIV resistant to first generation NNRTI (Efavirenz, Delavirdine. Nevirapine). Fusion inhibitors (Entry inhibitors) o Enfuvirtide binds to Gp41 subunit of HIV envelop protein and inhibits the fusion of viral and host cell membrane. o Maraviroc is a CCR5 Co-receptor antagonist and is only active against "CCR - 5 - tropic virus" which tends to predominate early in infection. Integrase inhibitors o Raltegravir and Elvitegravir act by inhibiting enzyme integrase.