There are five classes of drugs used to treat HIV/AIDS as of January 2015, according to AIDS.gov, including: integrase inhibitors, protease inhibitors, entry/fusion inhibitors, nucleoside/nucleotide reverse transcriptase inhibitors and non-nucleoside reverse transcriptase inhibitors. They are divided according to how they stop the replication of HIV.
Integrase inhibitors prevent integrase, an enzyme, from integrating the DNA created by the virus into the DNA of a person's cells, says AIDS.gov. This blocks the virus from making new viruses. Protease inhibitors prevent the enzyme protease from cutting the long threads of DNA into shorter pieces, blocking the virus from copying itself. Entry/fusion inhibitors prevent the virus from entering a person's CD4 cells by targeting the receptor sites on CD4 and HIV cells and keeping them from attaching and bonding to each other.
NRTIs, or nukes, behave like fake building blocks in viral DNA production, preventing the virus from using reverse transcriptase enzymes to build its DNA and copy itself, according to AIDS.gov. NNRTIs, or non-nukes, are similar to NRTIs. They block the reverse transcriptase enzymes to keep the virus from copying itself. However, they directly act on the enzymes and prevent them from functioning properly.
People who are taking a drug regimen to treat HIV/AIDS generally take three drugs from two of these classes. This is the standard of care, reports AIDS.gov, and does the best at protecting the immune system and controlling how much of the virus is in the body.