Nucala (Mepolizumab) Approved as HES Treatment

In late September, GlaxoSmithKline announced FDA approval of its treatment, Nucala, for patients with hypereosinophilic syndrome (HES). The treatment is safe for patients older than 12. Additionally, this approval is meaningful as Nucala now becomes the first biologic approved to treat HES.


Nucala (Mepolizumab) was first approved in 2015 to treat patients with severe eosinophilic asthma, a rare and severe form of asthma characterized by high eosinophil levels. Unlike other subtypes of asthma, severe eosinophilic asthma is often treatment-averse. Nucala is a monoclonal antibody which inhibits IL-5, thus reducing eosinophil levels. The Mayo Clinic defines monoclonal antibodies as:

laboratory-produced molecules engineered to serve as substitute antibodies that can restore, enhance or mimic the immune system.

Because Nucala works for conditions associated with eosinophilic inflammation, researchers believed it could be effective for patients with HES. This was studied in a Phase 3 clinical trial. Over a 7.3 month period, 108 patients received either 300mg Nucala subcutaneously every 4 weeks or a placebo. According to the data, Nucala reduced HES symptom flares by up to 50%.

While generally safe and well-tolerated, some adverse reactions did occur. In the Phase 3 HES trial, researchers noted injection site reactions. In clinical trials testing Nucala for severe eosinophilic asthma, adverse reactions included injection site reactions, fatigue, and headaches.

Hypereosinophilic Syndrome (HES)

Doctors are not sure of the exact cause of hypereosinophilic syndrome (HES), a rare blood disorder. Patients with HES have high levels of eosinophils, or white blood cells that play a role in immune function. Generally, patients must have heightened eosinophils for six months or more to receive an HES diagnosis. Males are impacted more than females. Around 5,000 people in the United States have HES. Symptom onset usually occurs between ages 20-50. Symptoms include:

  • Fatigue
  • Nausea and diarrhea
  • Heart disease and failure
  • Skin rashes
  • Fever
  • Memory loss and confusion
  • Respiratory disease
  • Lung inflammation
  • Blood clots
  • A persistent cough
  • Difficulty breathing
  • Nerve and brain damage

Learn more about HES.

Jessica Lynn

Jessica Lynn

Jessica Lynn has an educational background in writing and marketing. She firmly believes in the power of writing in amplifying voices, and looks forward to doing so for the rare disease community.

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