PANACOS' ANTIVIRAL STUDY FALLS SHORT OF GOAL

Panacos Pharmaceuticals has announced preliminary results from the first cohort of a Phase IIb study of bevirimat (PA-457) in patients failing HIV therapy due to drug resistance. The data confirm the clinical antiviral activity of bevirimat shown in previous studies; however, the bevirimat plasma concentrations were lower than anticipated, suggesting that the tablet formulation used for this study did not deliver the drug as expected.

After 14 days of dosing with 400 mg of bevirimat tablets administered on top of patients' background regimens, an antiviral effect was seen in the bevirimat treatment group. Two out of 12 patients with multiple-drug-resistant HIV who received bevirimat achieved an undetectable level of virus. These two patients and one other individual had a viral load reduction of greater than 1 log 10. However, the overall antiviral response in this first cohort was less than expected, in line with the patients' lower than anticipated bevirimat plasma concentrations.

A previous bioavailability study had predicted that the plasma concentrations, and therefore the antiviral response, of the 400-mg tablet dose would be comparable to the highest (200 mg) dose of the oral solution used in the Phase IIa study. Instead, both the plasma concentrations and the antiviral response observed in the 400-mg tablet cohort were similar to the 100-mg Phase IIa oral solution dose. The data suggest that the lower plasma concentrations of drug resulted from the properties of the 50-mg tablet, a prototype designed specifically for use in the Phase IIb trial. Preliminary analysis of the safety profile of bevirimat in the first cohort indicated that bevirimat was generally safe and well tolerated.