Trial of injectable flu drug yields disappointing results

Sep 20, 2007 (CIDRAP News) – BioCryst Pharmaceuticals, Inc, yesterday announced disappointing early results in a phase 2 study of its antiviral drug peramivir, which is seen as a potential new weapon against influenza.

Peramivir is a neuraminidase inhibitor that, unlike the licensed antivirals oseltamivir (Tamiflu) and zanamivir (Relenza), is given by intravenous (IV) or intramuscular (IM) injection. Many countries have stockpiled oseltamivir, an oral drug, and zanamivir, inhaled as a powder, in the hope that they will help if the H5N1 virus evolves into a human pandemic strain.

The phase 2 double-blind, placebo-controlled trial was designed to see if high doses of IM peramivir could reduce the duration of symptoms in patients with seasonal flu, BioCryst reported in a press release. The study involved 344 patients who had flu that was verified by rapid antigen testing. Patients were randomly assigned to receive injections of a placebo or either 150 mg or 300 mg of peramivir, administered in a single dose within 48 hours after symptom onset.

With 313 patients available for evaluation, researchers found that the peramivir group improved more than placebo group, but the difference was not statistically significant, BioCryst reported. The improvement over placebo was 22.9 hours in the 150-mg dose group and 21.1 hours in the 300-mg group.

The company said it believes the results were negatively affected by shorter needles—used for the phase 2 study but not for the phase 1 study—that may have delivered an adequate injection to only a third of the volunteers.

In a post hoc analysis of 101 patients who received an adequate IM peramivir injection, as measured by elevated serum creatine kinase over baseline, investigators found that improvement over placebo was 64.6 hours in the 300-mg dose group and 44.6 hours in the 150-mg group.

Safety and tolerability were similar for the placebo group and both peramivir groups, BioCryst said.

"We're clearly disappointed that we did not achieve the primary endpoint across the entire study population," said Jon P. Stonehouse, president and chief executive officer of BioCryst, based in Birmingham, Ala., in the statement. However, he added the company was buoyed by the safety findings and said the efficacy findings in the patients that received an adequate dose exceeded expectations.

BioCryst will correct the problems identified in the study when it launches a phase 3 study by the end of the year, he said.

Another phase 2 study is under way to evaluate the efficacy of IV peramivir in hospital patients with flu, the company said. The study is designed to compare IV peramivir with oral oseltamivir.

In January 2006 the US Food and Drug Administration (FDA) granted BioCryst a fast-track designation to develop an injection to treat highly virulent, life-threatening strains of influenza, the company said in its statement. In January 2007 the Department of Health and Human Services (HHS) awarded the company a $102.6 million contract to develop peramivir for seasonal and pandemic influenza.

Oct 2, 2006 CIDRAP News story "Injectable drug seen as potential treatment for flu, both seasonal and avian"