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
Resistance to zidovudine develops due to- 
Select and explain. 
A. Mutations at reverse transcriptase, B. Increased efflux of the drug from inside the cell, C. Increased metabolism of the drug, D. Decreased zidovudine 5 triphosphate formation
A: Mutations at reverse transcriptase
Answer: A: Mutations at reverse transcriptase 
Explanation: Ans. is 'a' i.e., Mutations at reverse transcriptase "Resistance to Zidovudine occurs by point mutation which alters reverse transcriptase enzyme. In the past when AZT was used alone, > 50% patients became nonresponsive to AZT within 1-2 years therapy due to growth of resistant mutants" - KDT