Dose Ranging Efficacy And Safety With Mepolizumab in Severe Asthma

The purpose of this study is to show whether mepolizumab given every 4 weeks intravenously (i.v.) can reduce the frequency of asthma exacerbations in subjects with severe asthma despite receiving high doses of standard asthma medications. The study will look at different doses of mepolizumab in comparison to a placebo.

A double-blind, placebo-controlled study to evaluate the efficacy, safety and pharmacodynamics of three doses (75 mg, 250 mg and 750 mg) of mepolizumab intravenous (i.v.) administered every 4 weeks compared with placebo over a 52-week treatment period in subjects with severe uncontrolled refractory asthma. Efficacy will be measured by the frequency of asthma exacerbations. In addition lung function, rescue medication usage, daily symptoms, asthma control score, asthma quality of life score and withdrawals due to asthma exacerbations will be assessed. Safety will be assessed by adverse events, clinical laboratory evaluations, ECGs, immunogenicity and vital signs. Pharmacodynamics will be assessed by eosinophil levels in blood, serum IL-5 and eosinophil levels in induced sputum.

Eligibility Criteria:
Inclusion Criteria:

* Male or female
* Aged 12 to 65 years inclusive
* Minimum weight 45kg
* Clinical features of severe refractory asthma
* Well documented requirement for high dose inhaled corticosteroids (ICS) \[i.e. \>= 880mcg/day fluticasone propionate or equivalent daily\] for at least 12 months
* Using additional controller medication in addition to high dose ICS for at least 12 months
* Persistent airflow obstruction indicated by a pre-bronchodilator FEV1\<80% predicted at visit 1 or 2 or peak flow diurnal variability of \>20% on 3 or more days during the run-in
* Airway inflammation which is likely to be eosinophilic in nature demonstrated by either raised peripheral blood eosinophils (\>=300/microL), sputum eosinophils (\>=3%), exhaled nitric oxide (\>=50ppb) or prompt deterioration of asthma control following a \<=25% reduction in regular maintenance dose of inhaled or oral corticosteroids (OCS)
* History of 2 or more exacerbations requiring systemic corticosteroids in the previous 12 months
* Evidence of asthma documented by airway reversibility, airway hyperresponsiveness or airflow variability
* ECG assessment demonstrating QTc\<450msec or QTc\<480msec for patients with bundle branch block
* Liver function tests demonstrating ALT\<2xUpper Limit of Normal (ULN), AST\<2xULN, Alk Phos \<=1.5xULN, bilirubin \<=1.5xULN
* Female of non-child-bearing potential or child-bearing potential with a negative pregnancy test at screening and prepared to agree to an acceptable method of contraception
* Able to give written informed consent
* Able to read, comprehend and write at a sufficient level to complete study materials

Exclusion Criteria:

* Current smokers or smoking history of \>=10 pack years
* Clinically important lung condition other than asthma
* Diagnosis of malignancy or in the process of investigation
* Unstable liver disease
* Churg-Strauss syndrome
* Using methotrexate, troleandomycin, oral gold, cyclosporine, azathioprine or any experimental anti-inflammatory therapy within 3 months of screening
* Omalizumab (Xolair) or any other biological for the treatment of inflammatory disease within 6 months of Visit 1
* Regular use of oral or systemic corticosteroids for diseases other than asthma within 12 months or any intra-articular, short-acting intramuscular corticosteroid within 1 month or intramuscular, long-acting depot corticosteroid within 3 months
* Allergy/intolerance to the excipients in the mepolizumab formulation
* Any investigational drug within 30 days or 5 terminal half-lives, whichever is longer
* Pregnant or breastfeeding or planning to become pregnant
* Clinically significant disease which is uncontrolled with standard treatment
* History of alcohol misuse or substance abuse
* Parasitic infestation within previous 6 months
* Known immunodeficiency
* Unable to follow instructions, use the electronic diary or peak flow meter
* Known evidence of lack of adherence to controller medications and/or follow physician's recommendations
* Previous participation in a study of mepolizumab and received study medication within 90 days