Fasenra (benralizumab) is an injectable biologic medication approved for the add-on maintenance treatment of severe eosinophilic asthma in adults and children aged 6 and older. It is also approved to treat eosinophilic granulomatosis with polyangiitis (EGPA), a rare blood vessel disease, in adults. Fasenra is not a rescue inhaler and cannot treat acute asthma attacks or breathing emergencies.
How Fasenra Works
Eosinophils are a type of white blood cell that, in healthy amounts, help fight infections. In some people with severe asthma, eosinophil levels climb far too high, triggering chronic airway inflammation that standard inhalers can’t fully control. This is called eosinophilic asthma.
Fasenra works by binding to a specific receptor on the surface of eosinophils. Once attached, it flags those cells for destruction by the immune system’s natural killer cells, a process called antibody-dependent cell-mediated cytotoxicity. The result is a direct, rapid, and nearly complete depletion of eosinophils. This is different from some other biologic asthma drugs that simply block the chemical signal telling the body to produce eosinophils. Fasenra eliminates the cells themselves.
Who Is Eligible
Fasenra is designed for people whose severe asthma is not well controlled despite high-dose inhaled corticosteroids combined with a long-acting bronchodilator. Before prescribing it, doctors typically check blood eosinophil levels. Clinical trials enrolled patients in a 2:1 ratio favoring those with baseline counts of 300 cells per microliter or higher, and this group showed the strongest response, with exacerbation reductions up to 51%. That said, patients with counts below 300 cells per microliter still showed benefit, so the threshold is not absolute.
The medication is approved for adults and children as young as 6 for asthma, and for adults only for EGPA.
How Well It Works
Three major clinical trials tested Fasenra against a placebo in people with severe eosinophilic asthma. In the SIROCCO trial over 48 weeks, patients on Fasenra experienced roughly half the rate of asthma flare-ups compared to placebo. In the CALIMA trial over 56 weeks, the reduction was about 28%. These differences were statistically significant, meaning they were unlikely to be due to chance.
For people dependent on daily oral steroids (like prednisone), the results were even more striking. In the ZONDA trial, patients on Fasenra had a 70% lower rate of exacerbations compared to placebo over 28 weeks. A larger follow-up study called PONENTE found that roughly 63% of patients were able to completely stop oral corticosteroids, and about 82% either eliminated them or reduced their dose to 5 mg or less per day. That matters because long-term oral steroid use carries serious side effects including bone loss, weight gain, and diabetes risk.
How Quickly Results Appear
Improvements in lung function can begin surprisingly fast. Across the three major trials, measurable improvement in morning peak airflow appeared as early as two days after the first injection. Clinically meaningful improvement, the kind patients actually notice in daily life, was reached within two to three weeks.
Dosing Schedule
Fasenra is given as a subcutaneous injection, meaning it goes just under the skin rather than into a vein. The standard schedule starts with one injection every four weeks for the first three doses. After that loading phase, the frequency drops to one injection every eight weeks for ongoing maintenance. Each dose is 30 mg.
The injection is available as a prefilled syringe or an autoinjector pen. Some patients receive it in a clinic, while others learn to self-inject at home after training from a healthcare provider. Each injection takes only seconds, and the autoinjector option can make self-administration easier for people uncomfortable with needles.
Common Side Effects
Fasenra is generally well tolerated. The most commonly reported side effects in clinical trials, each occurring in 1% to 10% of patients, include:
- Injection site reactions: pain, redness, itching, or a small bump at the injection site
- Headache
- Sore throat (bacterial or viral pharyngitis)
- Fever
- Cough
- Rash or hives
Serious allergic reactions are rare but possible. Signs include swelling of the face, mouth, or tongue, difficulty breathing, dizziness, or fainting. These reactions can occur within hours of an injection or, in some cases, days later. People with a known hypersensitivity to benralizumab or any of its inactive ingredients should not use Fasenra.
What Fasenra Does Not Do
Fasenra is a long-term controller, not a quick fix. It will not open your airways during an active asthma attack, and it should never replace a rescue inhaler. When starting Fasenra, you should continue all your existing asthma medications unless your doctor specifically adjusts them. Reducing inhaled or oral corticosteroids too quickly on your own can trigger a rebound worsening of symptoms or, in steroid-dependent patients, adrenal insufficiency.
It also does not work for all types of asthma. Because Fasenra specifically targets eosinophils, it is most effective in people whose asthma is driven by eosinophilic inflammation. People with non-eosinophilic severe asthma typically need a different treatment approach.