Why the FDA Approved an Asthma Drug To Treat Rare Blood Disorders

A drug traditionally used to treat severe asthma has been approved for hypereosinophilic syndromes (HES), making it the first medication approved to treat the group of rare blood disorders in almost 14 years.

On September 25, the Food and Drug Administration (FDA) approved Nucala (mepolizumab) for the treatment of HES in people 12 and older. Specifically, Nucala is indicated for those who've experienced HES for six months or longer.

What Are Hypereosinophilic Syndromes?

HES blood disorders are characterized by high levels of eosinophils, which are disease-fighting white blood cells. According to the American Academy of Allergy Asthma & Immunology, most healthy people have less than 500 eosinophils/microliter in their blood. But people with HES typically have over 1,500 eosinophils/microliter in their blood with no identifiable cause.

These extra eosinophils can make their way into organs like the skin, lungs, heart and nervous system, causing inflammation and eventually leading to organ dysfunction.

Symptoms of HES depend on the body part affected. If HES affects your skin, you may experience symptoms like eczema and hives. If HES affects your lungs, symptoms may include cough, shortness of breath, and wheezing.

How Nucala Can Help

In the case of severe asthma, Nucala works by preventing the excess formation of eosinophils, which cause airway inflammation. It does this by binding to a protein responsible for eosinophil regulation called interleukin (IL-5), blocking IL-5 from binding to receptors in the body.

Because eosinophils are also associated with HES, researchers wondered if Nucala could help. And results of a 2019 study conducted by pharmaceutical company GSK indicated it could.

“Mepolizumab [Nucala] is thought to work by reducing blood eosinophil levels, and evidence suggests it has potential as a targeted treatment option for a range of inflammatory diseases driven by raised eosinophils," Gerald Gleich, MD, an allergist, immunologist and HES expert with the University of Utah, said in a statement associated with the study. "These data are very promising and should provide hope for patients affected by this rare, life-threatening condition caused by eosinophilic inflammation," he added, describing HES.

In the randomized, double-blind study, 108 participants received either an injection of Nucala or a placebo every four weeks for 32 weeks in addition to standard of care treatment. While 56% of the placebo group experienced HES flares during the 8-month study, only 28% of the Nucala group experienced flares.

HES is typically treated with steroids or chemotherapy, the latter of which can have significant side effects. Some HES patients treated with Nucala reported only mild side effects, including upper respiratory tract infection and pain in extremities.