Safety and Efficacy Study of Mepolizumab in Churg Strauss Syndrome

Inclusion Criteria: * informed consent * documented history of Churg Strauss Syndrome * active disease * subjects must complete screening and baseline assessment * stable corticosteroid dose of \> 12.5 mg prednisolone for at least one week * treatment with cyclophosphamide (pulse or daily oral) or methotrexate or azathioprin or leflunomide in a stable dose for at least 4 weeks * not pregnant or nursing * negative pregnancy test and agree to practice birth control Exclusion Criteria: * life threatening disease or other critical illness deemed inappropriate for inclusion in the study by the principal investigator * treatment with other immunosuppressive agents within 4 weeks prior to randomisation * corticosteroid pulse of \> 60 mg within the last three weeks prior to randomisation * known secondary cause of eosinophilia * no history or clinical features of vasculitis * diagnosis of other primary systemic vasculitis * currently active malignant disease * abnormal laboratory values * impaired cardiac function * history of allergic reaction due to monoclonal antibodies * prior treatment with anti-hIL-5 monoclonal antibody * exposure to investigational drug within 30 days prior to randomisation * positive pregnancy test