Tenofovir disoproxil is a nucleotide analog reverse-transcriptase inhibitor (NtRTI).[15] It selectively inhibits viral reverse transcriptase, a crucial enzyme in retroviruses such as human immunodeficiency virus (HIV), while showing limited inhibition of human enzymes, such as DNA polymerases α, β, and mitochondrial DNA polymerase γ.[8][15] In vivo tenofovir disoproxil fumarate is converted to tenofovir, an acyclic analog of deoxyadenosine 5'-monophosphate (d-AMP). Tenofovir lacks a hydroxyl group in the position corresponding to the 3' carbon of the d-AMP, preventing the formation of the 5′ to 3′ phosphodiester linkage essential for DNA chain elongation.[15] Once incorporated into a growing DNA strand, tenofovir causes premature termination of DNA transcription, preventing viral replication.[15]
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