FDA Approves Mepolizumab for Rare Hypereosinophilic Syndrome

The FDA has approved mepolizumab to treat adults and children aged 12 and older with hypereosinophilic syndrome (HES) for 6 months or longer without another identifiable non–blood-related cause of the disease.

Mepolizumab is the first therapy in nearly 14 years to be approved for patients with this heterogenous group of rare disorders, which is associated with persistent eosinophilia and organ damage. Symptoms of HES can include congestive heart failure, deep vein thrombosis, and anemia. The treatment received orphan drug designation.

This approval is based on results from a phase III trial which compared the proportion of patients with at least one HES flare over a 32-week period in those treated with mepolizumab versus those receiving placebo. HES flares were defined as worsening symptoms or increasing eosinophils on at least two occasions. Fewer patients receiving mepolizumab experienced flares than patients in the placebo group (28% vs. 56%). The average time to first flare also was later in the mepolizumab group than the placebo group.

Adverse effects of mepolizumab include upper respiratory tract infection and extremity pain. The FDA advises clinicians to consider shingles vaccination for patients receiving mepolizumab, if medically appropriate.

Sources: FDA press release, September 25, 2020; ClinicalTrials.gov, “Intravenous Mepolizumab In Subjects With Hypereosinophilic Syndromes (HES).”