Description: Bevirimat (formerly known as PA-457, MPC-4326 and YK FH312), an analog of betulinic acid, is a novel and potent anti-HIV drug that acts as a maturation inhibitor. Existing antiretroviral treatments for HIV type-1 (HIV-1) disease are limited by problems of resistance and drug-drug interactions. Bevirimat has a mechanism of action that is distinct from other antiretroviral agents. Specific inhibition of the final rate-limiting step in Gag processing by bevirimat prevents release of mature capsid protein from its precursor (CA-SP1), resulting in the production of immature, non-infectious virus particles. Bevirimat inhibits replication of both wild-type and drug-resistant HIV-1 isolates in vitro, achieving similar 50% inhibitory concentration values with both categories. Serial drug passage studies have identified six single amino acid substitutions that independently confer bevirimat resistance. These resistance mutations occur at or near the CA-SP1 cleavage site, which is not a known target for resistance to other antiretroviral drugs. Bevirimat has demonstrated a consistent pharmacokinetic profile in healthy volunteers and HIV-infected patients, with peak plasma concentrations attained approximately 1-3 h after dosing. Plasma concentrations decrease in a log-linear manner with a mean plasma elimination halflife of 58-80 h, supporting once-daily dosing. Animal studies suggest that elimination of bevirimat is primarily by hepatic glucuronidation and hepatobiliary excretion. There is minimal renal elimination, with < 1% of the administered dose appearing in the urine. In responsive patients, bevirimat has demonstrated a robust dosedependent reduction in viral load (> 1.5 log10 copies/ml). Short-term administration (< or = 14 days) of bevirimat is well tolerated, even when used in combination with other antiretroviral agents. Further studies to evaluate the long-term efficacy and tolerability of bevirimat are currently underway.

References: Smith PF, et al. Phase I and II study of the safety, virologic effect, and pharmacokinetics/pharmacodynamics of single-dose 3-o-(3',3'-dimethylsuccinyl)betulinic acid (bevirimat) against human immunodeficiency virus infection. Antimicrob Agents Chemother. 2007 Oct;51(10):3574-81.