BioCryst Pharmaceuticals, Inc. completed its analysis of results from a study of a low dose of BCX5191 in chimpanzees to characterize its efficacy against the hepatitis C virus (HCV). In response to regulatory feedback, this experiment was designed to determine if non-toxic doses of BCX5191 would have a potent antiviral effect. Preclinical toxicology studies in rats had previously established a no observed adverse effect level, or NOAEL, of 0.5 mg/kg/day BCX5191.

In a preliminary experiment, uninfected chimpanzees were given a single 20 mg dose of BCX5191. The blood levels achieved with this dose were similar to those observed in rats at the NOAEL dose. Chimpanzees chronically infected with HCV were then dosed with 20mg/day BCX5191 for seven days and HCV RNA copies/mL measured daily.

Following seven days of treatment at that dose, the viral load reduction observed in the animals was insufficient to justify continued development. As a consequence, BioCryst is terminating its BCX5191 preclinical program, and the Company does not intend to pursue the development of BCX5191 or backup compounds against HCV.