Maraviroc is a chemokine receptor antagonist that is used in combination with other antiretroviral agents to treat human immunodeficiency virus type 1 (HIV-1) infection. Maraviroc exerts its therapeutic activity by blocking entry of the HIV-1 virus into immune cells—specifically the CD4-expressing T-helper cells, which play a major role in protecting the body from infection—precursor cells, and dendritic cells. HIV-1 infection is classified in two major forms according to the co-receptor it employs to gain entry in to the cell, namely the chemokine receptor 5 (CCR5) or the CXC chemokine receptor 4 (CXCR4). These co-receptors are expressed on different types of cells, and HIV tropism refers to the types of cells and tissues in which the virus infects and replicates. A tropism assay is conducted to determine which co-receptor the HIV-1 virus uses, i.e., whether the virus is CCR5-tropic, CXCR4-tropic, dual tropic (i.e., HIV-1 virus that is able to use both receptors), or mixed tropic (i.e., a mixture of HIV-1 viruses, some of which use CCR5 and others that use CXCR4). Maraviroc is only indicated for treatment of adults with CCR5 tropic HIV-1 and is not recommended when the CXCR4-tropic virus has been detected. The FDA-approved drug label for maraviroc states that “prior to initiation of maraviroc, test all patients for CCR5 tropism using a highly sensitive tropism assay”. [from
Medical Genetics Summaries]