There are five classes of drugs, which are usually used in combination, to treat HIV infection.
Use of these drugs in combination can be termed anti-retroviral therapy (ART), combination anti-retroviral therapy (cART), or highly active anti-retroviral therapy (HAART).

Anti-retroviral (ARV) drugs are broadly classified by the phase of the retrovirus life cycle that the drug inhibits. Typical combinations include 2 NRTIs as a "backbone" along with 1 NNRTI, PI, or INSTI as a "base."

Entry inhibitors (or fusion inhibitors) interfere with binding, fusion and entry of HIV-1 to the host cell by blocking one of several targets. Examples include maraviroc and enfuvirtide.

Nucleoside reverse transcriptase inhibitors (NRTI) and nucleotide reverse transcriptase inhibitors (NtRTI) are nucleoside and nucleotide analogues that inhibit reverse transcription. Examples include zidovudine, abacavir, lamivudine, emtricitabine, and tenofovir.

Non-Nucleoside reverse transcriptase inhibitors (NNRTI) inhibit reverse transcriptase by binding to an allosteric site of the enzyme. Examples include nevirapine and efavirenz (1st generation), and etravirine and rilpivirine (2nd generation)

Integrase inhibitors (also known as integrase nuclear strand transfer inhibitors, or INSTIs) inhibit the viral enzyme integrase, which is responsible for integration of viral DNA into the DNA of the infected cell. Examples include elvitegravir and dolutegravir.

Protease inhibitors (PI) block the viral protease enzyme necessary to produce mature virions upon budding from the host membrane. Examples include lopinavir, indinavir, nelfinavir, amprenavir, ritonavir, darunavir and atazanavir.

Adapted from Wikipedia, the free encyclopedia. Management of HIV/AIDS. Internet. Accessed on January 25, 2016.