Viro 4 Kit is used in the treatment of HIV infection. Viro 4 Kit is a combination of four antiviral medicines: Tenofovir disoproxil fumarate, Lamivudine, Atazanavir and Ritonavir. Tenofovir disoproxil fumarate and Lamivudine work by preventing HIV (virus) from multiplying, thereby reducing the amount of virus in your body. They also increase the CD4 cell (white blood cells that protect against infection) count in your blood. Atazanavir and Ritonavir work by interfering with an enzyme (protease), which is required by HIV-infected cells to make new viruses.