BACKGROUND: Interleukin (IL)-5 is believed to be a key cytokine in eosinophil 
inflammatory infiltration in asthma. Previous clinical trials have evaluated the 
efficacy and safety of mepolizumab, a monoclonal antibody against IL-5, in 
patients with asthma. However, most of these studies were small, the conclusions 
were inconsistent, and the precise effects are therefore debatable.
METHODS: A meta-analysis of randomized placebo-controlled trials was conducted 
to evaluate the effect of intravenous infusion of mepolizumab on clinical 
outcomes in patients with asthma. Trials were searched in PubMed, Embase, Web of 
Science, Cochrane CENTRAL, Scopus, reviews, and reference lists of relevant 
articles. The outcome variables analyzed included eosinophil counts in blood and 
sputum, airways outcome measures, exacerbations, asthma control, and quality of 
life scores.
RESULTS: Seven studies met final inclusion criteria (total n = 1131). From the 
pooled analyses, mepolizumab significantly reduced eosinophils in blood (MD 
-0.29×10(9)/L, 95% CI -0.44 to -0.14×10(9)/L, P = 0.0001) and sputum (MD -6.05%, 
95% CI -9.34 to -2.77%, P = 0.0003). Mepolizumab was also associated with 
significantly decreased exacerbation risk than placebo (OR 0.30, 95%CI 0.13 to 
0.67, P = 0.004), and with a significant improvement in the scores on the Asthma 
Quality of Life Questionnaire (AQLQ) (MD 0.26, 95% CI 0.03 to 0.49, P = 0.03) in 
patients with eosinophilic asthma. There were no statistical differences between 
the groups with respect to FEV1, PEF, or histamine PC20 (all P>0.05), and a 
non-significant trend for improvement in scores on the Juniper Asthma Control 
Questionnaire (JACQ) (MD -0.21, 95% CI -0.43 to 0.01, P = 0.06) in the 
mepolizumab group was observed.
CONCLUSIONS: Mepolizumab reduces the risk of exacerbations and improves quality 
of life in patients with eosinophilic asthma, but no significant improvement in 
lung function outcomes was observed. Further research is required to establish 
the possible role of anti-IL-5 as a therapy for asthma.