A Randomised, Double-blind, Parallel Group PhIII Study to Assess the Clinical Efficacy and Safety of 100 mg SC Mepolizumab as an Add on to Maintenance Treatment in Adults With Severe Bilateral Nasal Polyps - SYNAPSE (StudY in NAsal Polyps Patients to Assess the Safety and Efficacy of Mepolizumab)

Nasal polyps (NP) has long been known as chronic inflammatory disease of the nasal mucosa. This disease is characterized by the presence of polyps in the upper nasal cavity, originating from within the ostiomeatal complex. The presence of polyps can cause long-term symptoms such as prominent nasal obstruction, post-nasal drip, loss of smell, and discharge. Mepolizumab (SB240563) is an Immunoglobulin G 1 \[IgG1\], kappa humanized monoclonal antibody (mAB) that blocks human interleukin-5 (hIL-5) from binding to the interleukin-5 (IL-5) receptor complex expressed on the eosinophil cell surface and thus inhibits signaling. Neutralization of IL-5 with mepolizumab has been shown to reduce blood, sputum and tissue eosinophils and hence is assumed to be a treatment option in a number of eosinophilic diseases including NP. The aim of this randomized, double-blind, parallel group, phase 3 (PhIII) study is to assess the clinical efficacy and safety of 100 milligram (mg) subcutaneous (SC) mepolizumab as an add on to maintenance treatment in adults with severe bilateral NP. The study will include a 4-week run in period followed by randomization to a 52-week treatment period. Participants will receive mepolizumab 100 mg or placebo SC by the investigator or delegate via a pre-filled safety syringe every 4 weeks for 52 weeks. Throughout the entire study period (run in + treatment period + follow up), participants will receive a standard of care (SoC) for NP which consists of daily mometasone furorate (MF) nasal spray, and if required, saline nasal douching, occasional short courses of high dose oral corticosteroids (OCS) and/or antibiotics. The treatment period will consist of thirteen, 4-weekly doses of mepolizumab or placebo. In addition, up to the first 200 randomized participants will be followed up every other month for up to a further 6 months after the Visit 15 (7 months post last dose) in order to assess maintenance of response and to validate a physiological model derived from the previous Phase 2 study. Approximately 400 participants will be randomized (200 participants per treatment arm) in to the study. Total duration of the study will be 76 weeks for first 200 randomized participants and 52 weeks for remainder of participants who are not participating in the 6 months no treatment follow up.