Anti-HIV drugs act by blocking intracellular replication of the virus by inhibiting viral enzyme either reverse transcriptase or protease. Reverse transcriptase inhibitors belong to 3 different categories: nucleoside analogues, which active forms are the triphosphorylated intracellular compound, non nucleoside inhibitors and the more recent nucleotide analogues. Protease inhibitors are very active in vitro but besides their digestive side effects, have numerous drug interactions because they are metabolised through P450 liver cytochromes, and are associated with long-term toxicity.