[8][4] In studies, mepolizumab cut the necessity for hospitalisation due to asthma exacerbations in half, as compared to placebo.

[9] In December 2017, the FDA expanded mepolizumab's indication to treat adults with eosinophilic granulomatosis with polyangiitis, which is a rare autoimmune condition that can cause vasculitis.

[10] In September 2020, the FDA expanded mepolizumab's indication 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.

[11][12] The most common side effects in people with hypereosinophilic syndrome (HES) include: upper respiratory tract infection and pain in extremities (such as the hands, legs and feet).

[12] After subcutaneous injection, mepolizumab has an estimated bioavailability of 80% and reaches highest blood plasma concentrations after four to eight days.

[5] 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.

[15] Mepolizumab was evaluated in a randomized, double-blind, multicenter, placebo-controlled trial in 108 participants with hypereosinophilic syndrome (HES).