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Drug Categories
There are four main categories of antiretroviral (slows down HIV's progress) drugs that are generally used: nucleoside analogue reverse transcriptase inhibitors (NRTIs or Nukes), nonnucleoside reverse transcriptase inhibitors (NNRTIs or NonNukes), protease inhibitors (PIs), and fusion inhibitors.
NRTIs inhibit the synthesis of DNA of the HIV virus by reverse transcriptase, which is the viral enzyme that copies the RNA from the virus into DNA in the infected cell. Nucleoside analogues resemble the building blocks of DNA because of their structure: adenosine, gunosine (purines), thymidine, and cytidine (pyrimidines). Basically, NRTIs function as false nucleotides, causing the virus to attempt to use the drugs in the synthesis of viral DNA. When an NRTI has been incorporated into a DNA strand that is being synthesized, further nucleotides are prevented from being added to the strand. Thus, a copy of the viral DNA is not produced.
NNRTIs function similarly in the sense that they inhibit the synthesis of viral DNA, but they do not act as false nucleotides. Instead, they work by inhibiting the enzyme's activity by binding to reverse transcriptase.
PIs function by binding to the active sites of the viral protease enzyme. This prohibits the viral proteins from assuming functional forms by preventing them from being processed. Although viral particles are still produced when the protease is inhibited, these particles cannot form new cells.
Fusion inhibitors prevent HIV's entrance into target cells. Fusion inhibitors bind to a certain viral protein, gp41, which aids in viral entry to target cells. Because they block the gp41's interactions, these drugs interfere with the change that is necessary for HIV fusion with the target cell's membrane.
For facts pertaining to antiretroviral drugs in all four categories, please visit aidsinfonet.org's fact sheet.
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