Which of these is a nucleotide-analog reverse transcriptase inhibitor?

• A. Abacavir
• B. Emtricitabine
• C. Stavudine
• D. Tenofovir

Answer: (D)

Understanding the difference between nucleoside and nucleotide reverse transcriptase inhibitors helps explain why this one is the correct pick. Nucleoside RT inhibitors—like Abacavir, Emtricitabine, and Stavudine—need to be phosphorylated inside the cell to become active and then inhibit HIV reverse transcriptase. Tenofovir is a nucleotide analog, containing a phosphate group, and is taken up as a prodrug. Inside cells it’s converted to tenofovir diphosphate, which directly inhibits reverse transcriptase and terminates DNA synthesis. Because it’s a nucleotide analog, it fits the category described here, unlike the other three.