Nucala (mepolizumab) is a biologic injection that lowers levels of a specific white blood cell called eosinophils. It’s given as a shot under the skin once every 4 weeks and is FDA-approved to treat severe asthma, nasal polyps, and two rare blood conditions driven by eosinophil overproduction. Unlike everyday asthma inhalers, Nucala is a targeted therapy designed for people whose condition hasn’t responded well to standard treatments.
How Nucala Works
Eosinophils are white blood cells that play a role in fighting infections, but when your body produces too many of them, they cause chronic inflammation. In the lungs, this inflammation narrows airways and triggers asthma attacks. In the sinuses, it fuels polyp growth. In rarer conditions, excess eosinophils can damage organs throughout the body.
Nucala is a lab-made antibody that targets interleukin-5 (IL-5), a signaling protein your immune system uses to produce, activate, and sustain eosinophils. By binding to IL-5 and blocking its activity, Nucala cuts off the signal that tells your body to keep making these cells. Eosinophil levels drop, and the inflammation they cause decreases along with them.
Conditions It Treats
Nucala is approved for four distinct conditions, each involving eosinophil-driven inflammation:
- Severe eosinophilic asthma in patients aged 6 and older. This is the most common use. It’s specifically for people whose asthma remains uncontrolled despite high-dose inhalers and other controller medications.
- Chronic rhinosinusitis with nasal polyps (CRSwNP) in adults. Nasal polyps are soft growths in the sinuses that cause congestion, loss of smell, and recurring sinus infections.
- Eosinophilic granulomatosis with polyangiitis (EGPA) in adults. This is a rare autoimmune condition that inflames blood vessels and can affect the lungs, skin, nerves, and heart.
- Hypereosinophilic syndrome (HES) in adults. In HES, eosinophil counts stay dangerously high for months, potentially damaging the heart, lungs, skin, and nervous system.
How Well It Works for Asthma
In clinical studies, Nucala reduced the annual rate of asthma flare-ups by 34% to 38% compared with placebo. The benefit extends to serious episodes too: treatment was associated with a 36% reduction in exacerbations that led to hospitalization, consistent with broader analyses showing reductions of 45% to 72% in hospitalizations across different patient populations.
These numbers reflect averages. Some people experience dramatic improvement and go months without a flare-up, while others see more modest benefit. Nucala is not a rescue medication. It works in the background to prevent attacks, and it’s always used alongside your existing asthma treatments rather than replacing them.
Dosing by Condition
Nucala is given as a subcutaneous injection, meaning it goes just under the skin rather than into a vein. The dose depends on the condition being treated:
- Severe asthma (ages 12 and up): 100 mg once every 4 weeks
- Severe asthma (ages 6 to 11): 40 mg once every 4 weeks
- Nasal polyps: 100 mg once every 4 weeks
- EGPA and HES: 300 mg once every 4 weeks, given as three separate 100 mg injections spaced at least 2 inches apart on the body
For asthma and nasal polyps, each visit involves a single injection. For EGPA and HES, you’ll receive three injections per visit because the higher dose requires splitting it across multiple injection sites.
What the Injection Experience Is Like
Nucala can be administered at a doctor’s office, clinic, or at home using a prefilled autoinjector or prefilled syringe for the 100 mg dose. If you and your provider decide home administration is appropriate, you’ll be trained on proper injection technique first. Common injection sites include the upper arm, thigh, or abdomen.
Each appointment or self-injection session is quick. The injection itself takes only seconds. Because it’s given every 4 weeks, most people settle into a monthly routine. Children aged 6 to 11 receive the 40 mg dose, which requires reconstitution from a powder and is typically given by a healthcare provider rather than at home.
Common Side Effects
Nucala is generally well tolerated. In clinical trials for asthma, the most common side effects at rates of 3% or higher were:
- Headache: 19% (compared with 18% on placebo)
- Injection site reactions: 8% (pain, redness, swelling, or itching at the injection site, compared with 3% on placebo)
- Back pain: 5%
- Fatigue: 5%
- Muscle spasms: 3%
- Upper abdominal pain: 3%
Most of these side effects are mild. Injection site reactions are the most distinctive one, since headache and fatigue occurred at nearly the same rate in people receiving a placebo. The injection site discomfort typically resolves within a day or two. Serious allergic reactions are rare but possible, which is one reason your first few doses may be given in a clinical setting where you can be monitored.
Cost and Financial Assistance
Biologic medications like Nucala carry high list prices, but out-of-pocket costs vary widely depending on insurance coverage. For people with commercial insurance, a manufacturer copay program may bring costs as low as $0. The program also covers up to $100 per administration visit.
To qualify for the copay program, you need commercial (private) insurance and must be a U.S. resident. People enrolled in Medicare, Medicaid, VA, TriCare, or other government-funded prescription programs are not eligible. You can enroll through your healthcare provider or apply online through the Nucala copay program website.
What Nucala Does Not Do
Nucala is not a bronchodilator and won’t relieve an asthma attack in progress. You should continue carrying your rescue inhaler and using your other prescribed medications. It also isn’t approved for all types of asthma. It specifically targets eosinophilic asthma, so your provider will typically check your blood eosinophil levels before prescribing it to confirm it’s the right fit. Because Nucala suppresses part of your immune response, it’s important to stay current on any recommended vaccinations before starting treatment, as the medication may reduce your body’s ability to fight certain infections.