ANTIRETROVIRAL THERAPY FOR HIV AND AIDS.

Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. Different classes of antiretroviral drugs act at different stages of the HIV life cycle. Combination of several (typically three or four) antiretroviral drugs is known as Highly Active Anti-Retroviral Therapy (HAART). Antiretroviral drugs are broadly classified by the phase of the retrovirus life-cyle that the drug inhibits. There are thus five broad classifications of antiretroviral drugs in development, though only the first three classes currently have licensed examples:
* Reverse transcriptase inhibitors (RTIs) target construction of viral DNA by inhibiting activity of reverse transcriptase. There are two subtypes of RTIs with different mechanisms of action: nucleoside-analogue RTIs are incorporated into the viral DNA leading to chain termination, while non-nucleoside-analogue RTIs distort the binding potential of the reverse transcriptase enzyme.
* Protease inhibitors (PIs) target viral assembly by inhibiting the activity of protease, an enzyme used by HIV to cleave nascent proteins for final assembly of new virons.
* Fusion inhibitors block HIV from fusing with a cell's membrane to enter and infect it.
* Integrase inhibitors inhibit the enzyme integrase, which is responsible for integration of viral DNA into the DNA of the infected cell. There are several integrase inhibitors currently under clinical trial but none are commercially available.
* Entry inhibitors block HIV-1 from the host cell by binding CCR5, a molecule on the viral membrane termed a co-receptor that HIV-1 normally uses for entry into the cell.
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