Combivir tablets contain two active ingredients, zidovudine (also known as azidothymidine or AZT) and lamivudine (also known as 3TC). These are both medicines called nucleoside reverse transcriptase inhibitors. They are used in the treatment of HIV (human immunodeficiency virus) infection. AIDS (acquired immune deficiency syndrome) is caused by infection with HIV. This virus invades cells of the immune system, particularly the white blood cells known as CD4 T-helper lymphocytes. These cells normally work to activate other cells in the immune system to fight infection. Since HIV kills CD4 T-helper cells, over time the body becomes less able to fight the virus or subsequent infections.