Mepolizumab Steroid-Sparing Study in Subjects With Severe Refractory Asthma

This is a randomised, double-blind, placebo-controlled, parallel-group, multicenter study of mepolizumab in comparison with placebo in reducing Oral Corticosteroid (OCS) use in subjects with severe refractory asthma. The study consists of four phases, OCS Optimisation Phase (Week -8 to Week 0), and the double-blind treatment period divided into an Induction Phase (Week 0 to Week 4), OCS Reduction Phase (Week 5 upto Week 20) followed by Maintenance Phase (Week 20 to Week 24). During the Optimisation Phase the investigator will adjust the OCS (prednisone/prednisolone) dose according to the Optimisation titration schedule based on a review of Asthma Control Questionnaire (ACQ)-5 score and exacerbation. In the Induction Phase subjects will be randomized 1:1 (approximately 60 per arm) to receive either mepolizumab (100 mg) administered subcutaneously (SC) or placebo every 4 weeks in addition to their existing maintenance asthma therapy with the lowest dose of OCS from Optimisation Phase. The Induction Phase will allow sufficient time for those subjects randomised to the mepolizumab arm to achieve a decrease in the eosinophilic inflammation prior to the reduction in OCS. During the Reduction Phase, subjects will continue receiving 100 mg mepolizumab/placebo every 4 weeks and the OCS dose reduction will be done every 4 weeks using the reduction titration schedule based on a review of eDiary parameters recorded by the subject, the subjects' exacerbation history, and a review of the signs and symptoms of adrenal insufficiency. In the Maintenance Phase subjects will be maintained without any further OCS dose adjustment. Subjects who complete the 24 week double-blind period and meet the eligibility criteria, will be offered the opportunity to participate in an open label extension (OLE) study otherwise they will return for a Follow-up Visit 12 weeks after their last dose of double blind study treatment. At each clinic visit, adverse events, safety labs, spirometery parameters