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: Pharmacology
Nucleoside reverse transcriptase inhibiting drug, which is a guanosine analogue: March 2012 
Select and explain. 
A. Ritonavir, B. Zidovudine, C. Abacavir, D. Acyclovir
C: Abacavir
Answer: C: Abacavir 
Explanation: Ans: C i.e. Abacavir Anti-viral drugs and mechanism of action Ritonavir is a potent retroviral protease inhibitor Zidovudine is a thymidine analogue, the prototype of nucleoside reverse transcriptase inhibitors (NI) Abacavir, a guanosine analogue (nucleoside reverse transcriptase inhibitors), is a potent ARV drug that acts after intracellular conversion to carbovir triphosphate. Acyclovir is a deoxiguanosine analogue antiviral drug (anti-herpes), which requires a virus specific enzyme for conversion to the active metabolite that inhibits DNA synthesis and viral replication