Used in the treatment of HIV-1 infection, specifically for CCR5-tropic strains. It works by blocking the CCR5 co-receptor on human CD4 cells, preventing the virus from entering and infecting immune cells. Maraviroc is prescribed as part of combination antiretroviral therapy, particularly for patients who have failed prior treatments. It is effective only in individuals whose HIV uses the CCR5 receptor for cell entry, as determined by a prior diagnostic test.