Mepolizumab (Nucala) is now approved to treat adults and children ages 12 years and older with hypereosinophilic syndrome. It is the first new treatment for this condition in almost 14 years.

Hypereosinophilic syndrome is a heterogeneous group of rare blood disorders associated with persistent elevations of eosinophils with demonstrated organ damage. The damage, which can occur in any organ system, occurs when eosinophils enter the organ system. The most commonly affected systems are the heart, the central nervous system, the skin, and the respiratory tract. The disorder has been previously treated with imatinib mesylate (Gleevec). Mepolizumab is also approved as treatment for adults with eosinophilic granulomatosis with polyangiitis and for patients ages six years and older as add-on maintenance treatment for severe asthma with an eosinophilic phenotype.

Mepolizumab is an interleukin-5 antagonist monoclonal antibody. Interleukin-5 is the major cytokine responsible for growth and differentiation, recruitment, activation, and survival of eosinophils. Mepolizumab reduces the production and survival of eosinophils as it blocks interleukin-5 activity.

Mepolizumab was approved based on a randomized, double-blind, placebo-controlled trial of 108 patients with hypereosinophilic syndrome. The trial compared the number of flares between the two groups over a 32-week period. A hypereosinophilic syndrome flare is a worsening of signs or symptoms or an increase in eosinophils on at least two occasions. Fewer patients who received mepolizumab had flares compared with those receiving placebo (28% versus 56%). The time to the first flare was later, on average, for those receiving mepolizumab compared with those receiving placebo.

The most common adverse effects of mepolizumab reported in clinical trials were headache, injection site reactions, back pain, and fatigue. Hypersensitivity reactions and herpes zoster infections are also possible.

Mepolizumab is given subcutaneously. Nurses who administer mepolizumab using the single-dose vials should read the label for directions on reconstitution and administration of the drug. Patients receiving prefilled autoinjectors for home use will need education on the proper use of the device. NPs should encourage vaccination for herpes zoster prior to starting mepolizumab to prevent infection.

For complete prescribing information for mepolizumab, go to http://www.accessdata.fda.gov/drugsatfda_docs/label/2020/125526s017lbl.pdf