Pharmacokinetics and Pharmacodynamics of Mepolizumab Administered Subcutaneously in Children

Mepolizumab is a humanized immunoglobulin G (IgG1) monoclonal antibody (mAb) that exhibits dose proportional and time-independent pharmacokinetics. The study will be conducted in 2 parts. Part A: it will be pharmacokinetic (PK) and pharmacodynamic (PD) study conducted to support the use of mepolizumab in children aged 6 to 11 years with severe eosinophilic asthma and characterize the PK/PD of mepolizumab 40 milligrams (mg) or 100 mg administered subcutaneously depending on participant body weight. Part B: It is a long-term safety / pharmacodynamic phase in which extended treatment for a further 52 weeks will be offered on an optional basis to those subjects eligible for continued treatment. Participants with bodyweight \=40 kg will be dosed with mepolizumab 100 mg subcutaneously in upper arm or thigh at Visit 2 (Week 0). Approximately 40 male or female participants aged 6 to 11 years will be screened to achieve approximately 28 eligible participants entering the treatment phase to allow availability of 20 evaluable participants, with a minimum of six participants enrolled in the \<40 kg bodyweight group. The total duration of the study will be 22 weeks and will include a run-in period of 1-2 weeks, a treatment period of 12 weeks and a follow-up phase of 8 weeks. A participant will be considered having completed the study if the participant completes all phases of the study including the follow-up phase (Week 20 \[visit 8\]).