days in different individuals. Chemistry The substance is an IgG1 kappa monoclonal antibody, the two heavy chains consisting of 449 amino acids each, and the two light chains consisting of 220 amino acids each. The protein part has a molar mass of about 146 kDa, and the sugar part of 3 kDa. History Phase III clinical trials in severe eosinophilic asthma were completed in 2014. The FDA approved it in November 2015. The European Commission granted a marketing authorization valid throughout the European Union on 2 December 2015. Mepolizumab was approved for medical use in the European Union in December 2015. In September 2020, mepolizumab was approved in the United States to treat adults and children aged twelve years and older with hypereosinophilic syndrome (HES) for six months or longer without another identifiable non-blood related cause of the disease. Mepolizumab was evaluated in a randomized, double-blind, multicenter, placebo-controlled trial in 108 participants with hypereosinophilic syndrome (HES). In the study, participants were randomly assigned to receive mepolizumab or placebo by injection every four weeks. The trial compared the proportion of subjects who experienced a HES flare during the 32-week treatment period. A HES flare was defined as worsening of clinical signs and symptoms of HES or increasing eosinophils (disease-fighting white blood cells) on at least two occasions. The trial compared the proportions of participants with at least one flare over a 32-week treatment period, as well as the time to the first flare. Fewer participants in the mepolizumab treatment group (28%) had HES flares compared to participants in the placebo group (56%), with a 50% relative reduction. In addition, the time to the first HES flare was later, on average, for participants treated with mepolizumab versus placebo. Research Mepolizumab has been investigated or is under investigation for the treatment of atopic dermatitis, hypereosinophilic syndrome (HES), eosinophilic esophagitis (EoE), nasal polyposis, eosinophilic granulomatosis with polyangiitis, and chronic obstructive pulmonary disease. References External links Antiasthmatic drugs GSK plc brands Immunosuppressants Monoclonal antibodies Orphan drugs