Glaxosmithkline plc (GSK), of London, said a pivotal phase III study of mepolizumab, an investigational IL-5 antagonist monoclonal antibody, met its primary endpoint of reducing the frequency of exacerbations in patients with severe eosinophilic asthma. The study evaluated the efficacy of two dose regimens of mepolizumab in patients with severe eosinophilic asthma. Patients remained on their current asthma maintenance therapy throughout the study and were randomized to mepolizumab 75 mg intravenous (I.V.), 100 mg subcutaneous (SC) or placebo every four weeks. For the primary endpoint, both mepolizumab treatment arms showed statistically significant reductions in the frequency of clinically significant exacerbations of asthma compared to placebo (75 mg I.V., 47 percent, p < 0.001; 100 mg SC, 53 percent, p < 0.001). Adverse events were similar across all treatment groups, mostly nasopharyngitis, headache, upper respiratory tract infection and asthma. A second phase III study designed to evaluate mepolizumab 100 mg SC every four weeks vs. placebo in reducing daily oral corticosteroid use while maintaining asthma control also met its primary endpoint, showing that patients on the study drug were able to achieve greater reductions in their maintenance oral corticosteroid dose during weeks 20 to 24 compared to patients on placebo (p = 0.008), while maintaining asthma control. GSK said it plans to present full results at an undisclosed scientific meeting.