In the trial the drug, an oral endothelin receptor antagonist, met the primary efficacy endpoint of improved exercise capacity, the key secondary endpoint of time to clinical worsening and several other secondary efficacy endpoints.
After 12 weeks of once-daily dosing with 5mg of the drug, patients were able to walk an average of a further 59.4 meters in a six minute walk test. Patients who received a 2.5mg dosing had an improved six minute walk distance of 32.3 meters, whilst the performance of patients who received only placebo decreased by an average of 10.1 meters.
Ambrisentan also proved to be generally well tolerated in the trial. The most frequent adverse event was headache, which occurred in 12.7% of patients in the 5 mg dose group and 7.8% in the 2.5 mg dose group, compared to 6.2% in the placebo group.
“The magnitude of improvement in six-minute walk distance and dose-response for the primary endpoint were impressive,” said Dr Michael Gerber, Senior vice president of Clinical Development and Regulatory Affairs for Myogen. “These results and those of our long-term phase II trial suggest that, if approved, ambrisentan could ultimately represent a major treatment advance for patients with pulmonary arterial hypertension.”