The active ingredient of Ziagen is abacavir sulfate, which belongs in the nucleoside reverse transcriptase inhibitor (NRTI) class of antiretroviral drugs.
Abacavir sulfate in cells gets converted into carbovir triphosphate, an analogue of deoxyguanosine-5′-triphosphate, one of the four nucleotides from which DNA assembles. When viral RNA is reverse-transcribed into DNA in the cell, carbovir triphosphate gets incorporated in the place of deoxyguanosine-5′-triphosphate into the DNA that is being synthesised. When this happens, DNA synthesis is halted, as the next nucleotide can not form a bond with carbovir triphosphate (this DNA synthesis halt is called chain termination).
Ziagen was shown to decrease the levels of HIV RNA in the body, and to increase the levels of CD4+ cells (cells of our immune system and one of the main targets of HIV – their levels normally decrease after an HIV infection).