 The drugs belong to six different classes that act at different targets.The most popular target in the field of antiretroviral drug development is the HIV-1 reverse transcriptase (RT) enzyme.There are two classes of drugs that target the HIV-1 RT enzyme, nucleoside/nucleotide reverse-transcriptase inhibitors (NRTIs/NtRTIs) and non-nucleoside reverse-transcriptase inhibitors (NNRTIs).