Pharmacology: Tenofovir disoproxil fumarate is an acyclic nucleoside phosphonate diester analog of adenosine monophosphate. After phosphorylation to the active tenofovir diphosphate form, it inhibits the activity of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase and hepatitis B virus (HBV) reverse transcriptase by competing with the natural substrate deoxyadenosine 5'-triphosphate and terminates the deoxyribonucleic acid (DNA) chain after incorporation into viral DNA.