Nucleoside Analogues
The first effective class of antiretroviral drugs was the nucleoside analogues. They act by incorporating themselves into the DNA of the virus, thereby stopping the building process. The resulting DNA is incomplete and cannot create new virus.
Protease Inhibitors
Protease inhibitors work at the last stage of the virus reproduction cycle. They prevent HIV from being successfully assembled and released from the infected CD4+ cell.
Non-Nucleoside Reverse Transcriptase Inhibitors
Non-nucleoside reverse transcriptase inhibitors (NNRTIs) stop HIV production by binding directly onto reverse transcriptase and preventing the conversion of RNA to DNA. These drugs are called "non-nucleoside" inhibitors because even though they work at the same stage as nucleoside analogues, they act in a completely different way.
Nucleotide Reverse Transcriptase Inhibitors
Nucleotides and nucleoside reverse transcriptase inhibitors (NRTIs) have a similar mechanism of action. Unlike the nucleoside analogs, however, the nucleotide reverse transcriptase inhibitors are chemically pre-activated with the presence of phosphate group. Since the phosphorylation step is not necessary, nucleotide analogs can incorporate into viral DNA chain more rapidly than nucleoside analogs. More importantly, this will bypass a viral mechanism of nucleoside resistance.