Atazanavir is an oral medication that is used for treating infections caused by the human immunodeficiency virus(HIV). It is in a class of drugs called protease inhibitors that also includesritonavir , nelfinavir (Viracept), indinavir (Crixivan) and saquinavir(Invirase, Fortovase). During infection with HIV, the HIV virus multiplies within the body's cells. Viruses are released from the cells and spread throughout the body where they infect other cells. In this manner, HIV infection is perpetuated among new cells that the body produces continually. During the production of the viruses, new proteins must be made. Some of the proteins are structural proteins, that, is, proteins that form the body of the new viruses. Other proteins are enzymes that manufacture DNA and other components for the new viruses. Protease is the enzyme that forms the new structural proteins and enzymes. Atazanavir blocks the activity of protease and results in the formation of new viruses with defective proteins that are unable to infect the body's cells. As a result, the number of viruses in the body (the viral load) decreases. Nevertheless, atazanavir does not prevent the transmission of HIV among individuals, and it does not cure HIV infections or AIDS. Atazanavir was approved by the FDA in June 2003.

atazanavir sulfate is an azapeptide inhibitor of HIV-1 protease.

The chemical name for atazanavir sulfate is (3S,8S,9S,12S)-3,12-Bis(1,1-dimethylethyl) -8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl)phenyl]methyl]-2,5,6,10,13- pentaazatetradecanedioic acid dimethyl ester, sulfate (1:1). Its molecular formula is C38H52N6O7•H2SO4, which corresponds to a molecular weight of 802.9 (sulfuric acid salt). The free base molecular weight is 704.9. Atazanavir sulfate has the following structural formula:

Atazanavir sulfate is a white to pale yellow crystalline powder. It is slightly soluble in water (4–5 mg/mL, free base equivalent) with the pH of a saturated solution in water being about 1.9 at 24 ± 3° C.