Maraviroc: a new CCR5 antagonist.

Maraviroc is a small molecule and a member of a new class of antiretroviral compounds known as CCR5 antagonists, which block R5-tropic HIV entry into CD4 cells. HIV entry into the cell requires binding to a CD4 molecule and, in the majority of cases, to a coreceptor, either chemokine coreceptor 4 (CXCR4) or 5 (CCR5). In August 2007, the US FDA approved maraviroc for use in combination with other antiretroviral agents for treatment-experienced adults infected with CCR5-tropic HIV-1 only and who have evidence of viral replication. Maraviroc prevents the virus from entering uninfected cells by blocking the CCR5 coreceptor. Maraviroc has two dose formulations (150- and 300-mg tablets) and can be taken with or without food. The dosing recommendations are based on concomitant medications due to drug interactions. It is excreted primarily in the feces, with approximately 25% via urine. The safety and efficacy of maraviroc have not been established in pregnant women or pediatric patients. Maraviroc has been shown to achieve an undetectable HIV-1 RNA level in clinically advanced, class 3 antiretroviral treatment-experienced adults with evidence of CCR5-tropic HIV-1 replication despite ongoing antiretroviral therapy. It is generally well tolerated and its development is responding to a desperate need for new classes of antiretroviral agents that can target novel steps of the HIV lifecycle and do not share crossresistance with currently available therapy.