7 Things to Know About Mepolizumab (Nucala)

Medically Reviewed by Neha Pathak, MD on May 04, 2023

Mepolizumab (Nucala) is a drug doctors can prescribe to help manage severe asthma symptoms and treat certain other inflammatory and blood conditions. Here are seven things to know about this medication.

Mepolizumab is used to treat health conditions that can happen when you have too many eosinophils, a type of white blood cell. They are: 

  • A serious type of asthma, called severe eosinophilic asthma, in adults and in children 6 and older 
  • Chronic rhinosinusitis with nasal polyps (growths in your nose) in adults. This condition causes congestion and swelling in your sinuses.  
  • Eosinophilic granulomatosis with polyangiitis (EGPA) in adults. When you have this condition, you have asthma along with swelling in your blood vessels. 
  • Hypereosinophilic syndrome (HES), a group of blood disorders, in adults and children 12 and older

You’ll take mepolizumab as a 100-milligram shot every 4 weeks. Children younger than 11 often take a 40-milligram shot. The dosage may vary based on your age, size, and what health condition you have. 

Your doctor or a nurse will give you your first treatment. They can inject it into your arm, abdomen (stomach area), or thigh. The shot goes just underneath your skin. You’ll need to stay at the doctor’s office for a few minutes after the treatment so they can watch for any allergic reactions. 

After that, you may be able to inject the medication yourself at home. You can get the drug from a specialty pharmacy and store it in your refrigerator until you’re ready to use it.

For adults, the medicine comes in an autoinjector, a one-use, disposable spring-loaded syringe, which hides the needle and makes it easier for some people to take the drug themselves. It also comes in a prefilled syringe. 

A parent or caregiver can inject the medication (via a pre-filled syringe) in children ages 6-11. 

If you choose to do the treatment at home, your doctor will teach you:

  • How to inject the drug properly
  • What steps to take to make sure your medication is safe and ready for use
  • Possible signs of an allergic reaction 

Most potential side effects of mepolizumab are mild. They may go away as your body gets used to the drug.

One of the most common side effects is irritation, redness, or swelling of the skin where the shot was given. 

For people with asthma, EGPA, and HES, other side effects include headaches, back pain, and fatigue. People taking the drug for chronic rhinosinusitis with nasal polyps (CRSwNP) may have a sore throat and joint stiffness or discomfort. 

Serious allergic reactions and side effects are rare. If you show signs of a severe allergic reaction, such as intense swelling (especially to the mouth, tongue, and throat), dizziness, or trouble breathing, get medical help right away. 

Mepolizumab is meant to be used in addition to other asthma treatments such as corticosteroids and inhalers. Mepolizumab can help improve your overall symptoms and lessen serious flare-ups. But it can’t treat a sudden flare-up of symptoms during an asthma attack. You’ll need to keep taking your other asthma medications and use your inhaler to treat asthma attacks and flare-ups. 

Over time, if your asthma symptoms improve, your doctor may suggest lowering your dose of steroids or other asthma medications. Follow your doctor's instructions and always talk to them  before reducing or stopping any steroid medication. Your asthma can get worse if you stop taking these medicines suddenly. 

Some people who take the drug have reported getting shingles, a painful rash caused by a reactivation of the herpes zoster (chickenpox) virus. Be sure to talk to your doctor about whether you’ve had shingles and whether you should get a vaccine before taking the drug.

Let your doctor know if you’ve had worms or other parasitic infections. Mepolizumab might weaken your immune system’s response to these infections. If you have a parasitic infection, get treatment before you start mepolizumab. 

Tell your doctor if you’re pregnant, plan to get pregnant, or are breastfeeding. Scientists aren’t sure whether mepolizumab is safe during pregnancy. At the same time, uncontrolled asthma is also risky during pregnancy. Your doctor can discuss the pros and cons of taking the medication with you. 

We do know that drugs like mepolizumab pass through the placenta during pregnancy, and there may be a greater chance of harm during the second and third trimesters. Doctors don’t have information about the drug’s possible effects on breastfed infants or on milk production.

While experts don’t completely understand how mepolizumab works, we do know that it helps reduce your body’s production of eosinophils. While these white blood cells help fight infection as part of your immune system, too many of them cause harmful inflammation. And inflammation is a key component of severe eosinophilic asthma and the other conditions this medication treats. 

The drug binds to a protein in your body that produces eosinophils and blocks it from making more of them. Mepolizumab also helps keep existing eosinophils from surviving.

In clinical trials, people with asthma who took mepolizumab had fewer serious asthma attacks, including attacks that sent them to a hospital. 

In one study, people who took 100-milligram doses of mepolizumab had 47%-53%  fewer serious attacks than those who took a placebo (a fake treatment). 

Show Sources


FDA: Mepolizumab label.

Pharmacy & Therapeutics: “Mepolizumab (Nucala) For Severe Eosinophilic Asthma.”

Medline Plus: “Mepolizumab Injection.” 

Nucala: “Nucala Autoinjector,” “Why Nucala?” “Risks & side effects,” “How does Nucala work?”

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