<unk>  is an analogue of cytidine. It can inhibit both types (1 and 2) of HIV reverse transcriptase and also the reverse transcriptase of hepatitis B virus. It is phosphorylated to active metabolites that compete for incorporation into viral DNA. They inhibit the HIV reverse transcriptase enzyme competitively and act as a chain terminator of DNA synthesis. The lack of a 3'-OH group in the incorporated nucleoside analogue prevents the formation of the 5' to 3' phosphodiester linkage essential for DNA chain elongation, and therefore, the viral DNA growth is terminated.<unk>  is administered by mouth, and it is rapidly absorbed with a bio-availability of over 80%. Some research suggests that<unk>  can cross the blood–brain barrier.<unk>  is often given in combination with zidovudine, with which it is highly synergistic.<unk>  treatment has been shown to restore zidovudine sensitivity of previously resistant HIV.<unk>  showed no evidence of carcinogenicity or mutagenicity in in vivo studies in mice and rats at doses from 10 to 58 times those used in humans. It has a half-life of 5–7 hours in adults and 2 hours in HIV-infected children.
Lamivudine
Telbivudine
Sorivudine
Saquinavir
Fosamprenavir
Abacavir
Maribavir
Indinavir