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Fasenra: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on March 28, 2023.

1. How it works

  • Fasenra is a brand (trade) name for benralizumab which is a biologic that may be used to treat severe eosinophilic asthma.
  • Fasenra is a monoclonal antibody (IgG1, kappa) that binds to IL-5Rα, the alpha subunit of the human interleukin-5 receptor. By binding to IL-5Rα, Fasenra prevents IL-5 from binding and its alpha and beta subunits from interacting. IL-5 is the main cytokine responsible for the growth and differentiation, recruitment, activation, and survival of eosinophils. Cytokines are small secreted proteins that are involved in cell signaling and interactions. By binding to IL-5, Fasenra reduces the production and survival of eosinophils. Eosinophils are one of multiple types of cells and mediators that are involved in inflammation, and inflammation is an important component in the pathogenesis of asthma and some other conditions.
  • Fasenra also binds to and activates the FcγRIIIa receptor on another type of white blood cell called natural killer (NK) cells. This enhances apoptosis, or programmed cell death, of eosinophils via a process called antibody-dependent cell-mediated cytotoxicity (ADCC). It also enhances the apoptosis of basophils. Basophils are yet another type of white blood cell. They also express IL-5Rα like eosinophils do and play a role in the airway inflammation associated with asthma. They also express IL-5Rα like eosinophils do and play a role in the airway inflammation associated with asthma. The exact way Fasenra works in asthma has not been definitively established.
  • Fasenra belongs to the class of medicines known as interleukin inhibitors. It may also be called a monoclonal antibody.

2. Upsides

  • May be used as an add-on maintenance treatment for severe eosinophilic asthma in adults and children aged 12 years old and older. This is a subtype of asthma that is characterized by high numbers of eosinophils in the blood. Eosinophils are a type of white blood cell and this type of asthma affects 5% of all asthmatics.
  • Given via subcutaneous injection (under the skin). After an initial loading dose where Fasenra is injected once every 4 weeks for the first 3 doses, it only needs to be given once every 8 weeks. The usual dosage for severe eosinophilic asthma is 30mg every 8 weeks for adults and children aged at least 12 years.
  • Available as a 30 mg/mL single-dose prefilled syringe designed for health professionals and a 30 mg/mL single-dose autoinjector pen (an automatic injection).
  • People can be taught how to self-administer Fasenra.
  • Weight gain is not reported as a side effect of Fasenra in the product information. However, anecdotally, some people have reported a small amount of weight gain on blog sites, although equally as many people report weight loss as well, usually because they no longer need to take as much prednisone.
  • Neither the prefilled syringe (including stopper and cap) nor the autoinjector is made with natural rubber latex, so these can be safely handled by people with latex allergies.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Headaches, fever, pharyngitis (inflammation of the back of the throat), and injection site reactions (redness, pain, itching, or swelling at the injection site), are the most common side effects reported with Fasenra. Rarely, allergic reactions may occur.
  • Must be given by subcutaneous injection, although people can be taught how to self-administer the Fasenra autoinjector.
  • Fasenra will not treat an asthma attack or exacerbations of asthma (acute bronchospasm or status asthmaticus). Seek medical advice if your asthma worsens while on Fasenra.
  • Fasenra is not indicated for the treatment of other eosinophilic conditions such as eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome) or hypereosinophilic syndrome (HES).
  • Serious hypersensitivity reactions (such as angioedema and urticaria) have been reported in people administered Fasenra, usually within hours of administration but sometimes days later. A health professional should always administer the first dose of Fasenra and patients should be advised to seek urgent emergency help if they experience an allergic-type reaction and Fasenra has needed to be discontinued.
  • People prescribed Fasenra may not require the same dosages of systemic or inhaled corticosteroids (ICS). However, these should not be discontinued abruptly. Instead, reductions should be gradual and performed under the direct supervision of a physician. Be aware that corticosteroid dosage reductions may be associated with withdrawal symptoms or unmask conditions previously suppressed by corticosteroid therapy.
  • Fasenra may influence a person's response to parasitic infections because eosinophils may be involved in the immunological response to these infections. Treat any existing parasitic infections before starting Fasenra. If patients become infected during treatment with Fasenra and do not respond to anti-helminth treatments, discontinue Fasenra until the infection resolves.
  • Research has shown approximately 12% of people receiving Fasenra develop antibodies to it, which has been associated with increased clearance of Fasenra and increased blood eosinophil levels. However, no evidence of an association between anti-drug antibodies with efficacy or safety was observed.
  • It is unknown what effect Fasenra has during pregnancy on the unborn child. There are no data on the effect of Fasenra during lactation. The risks vs benefits need to be weighed up. Any woman that does become pregnant while being administered Fasenra should enroll in the pregnancy exposure registry by calling 1-877-311-8972 or visiting There is no information on the safety of Fasenra during breastfeeding.
  • No generic of Fasenra is currently available.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Fasenra is a biologic that works by blocking the action of IL-5 which is the main cytokine responsible for the survival and production of eosinophils. Fasenra may be used to treat severe eosinophilic asthma and after an initial loading dose, may be self-administered every eight weeks using a Fasenra autoinjector pen. Common side effects include headache, fever, pharyngitis, and injection site reactions.

5. Tips

  • Fasenra is usually given once every two months (eight weeks). Initially, your doctor will administer it, but during your appointment, they will discuss teaching you how to administer the Fasenra autoinjector pen so that you can administer it at home. This will save you from going to your doctor every two months.
  • Keep Fasenra in the refrigerator at 36°F to 46°F (2°C to 8°C) before use. Keep it in its original carton to protect it from light. Do not freeze. Do not shake. Avoid exposure to heat. Before using, take one Fasenra autoinjector out of the refrigerator, and leave it to warm up to room temperature for 30 to 40 minutes. Do not heat it in direct sunlight, the microwave, or in hot water because this will ruin the medicine. A Fasenra autoinjector may be stored in its original carton outside the refrigerator at up to 77°F (25°C) for up to 14 days. But it should be discarded if not used within this time and should not be put back into the refrigerator.
  • Do not use the medicine if it is cloudy or has passed its expiry date. The medicine should look clear to pale yellow and may contain a few translucent white to off-white particles.
  • Only inject into clear, healthy skin. Do not inject into any areas that are bruised, tender, red, scaly, or hard. You should also not inject into scars, stretch marks, or areas of eczema.
  • Fasenra can be self-injected into the thighs or abdomen. If you are a caregiver administering Fasenra to another person, it may also be administered into the upper arm. Wash your hands and clean the injection site with an alcohol swab.
  • To administer the Fasenra autoinjector pen, first, remove the clear needle cap from the end of the autoinjector by pulling it off. Do not touch the green needle guard on the end because this may set off the injection prematurely. Hold the autoinjector straight up and down (at a 90° angle) onto your preferred injection site, if you want to, you can gently pinch the skin up at the injection site. To start the injection push the autoinjector all the way down while holding it against your skin. You should hear a click to let you know the injection has started. Your injection may take up to 15 seconds to complete. Continue to hold it down until you hear a second click and the inspection window is filled with the green indicator. After you hear the second click, continue to hold it down for 5 more seconds. Remove the autoinjector. There may be a small drop of blood at the injection site but this is normal. Do not rub your injection site. Do not put the clear cap back on the autoinjector. Throw the autoinjector away in an FDA-cleared sharps disposal container or another suitable sharps container.
  • If you think you are gaining weight on Fasenra, keep a diary that documents your daily diet, amount of exercise, and daily weight gain. Try to eat a healthy diet and exercise regularly. If there is a clear pattern of weight gain, talk with your doctor.
  • Seek urgent medical attention if you experience shortness of breath, or facial or throat tightness after administering Fasenra. If you feel unwell, or experience other signs of infection, tell your doctor immediately. Also remember to tell your doctor about any other side effects that you may be experiencing, such as headache or back pain.
  • Fasenra does not treat an asthma attack or worsening asthma. Seek medical advice if your asthma remains uncontrolled or worsens after initiation of treatment with Fasenra.
  • If you have a parasitic infection, it should be treated before you start Fasenra.
  • Tell other health professionals that you are being administered Fasenra. Fasenra may increase your risk of herpes infection. If you are at high risk, your doctor may consider vaccination against herpes.
  • It is unknown what effect Fasenra has on an unborn baby. Tell your doctor immediately if you become pregnant while being administered Fasenra and enroll in the Pregnancy Exposure Registry by calling 1-877-311-8972 or by visiting
  • Talk to your doctor or pharmacist before taking any other medicines with Fasenra. Do not change any other medications, such as reducing your corticosteroid dosage, without talking to your doctor first.

6. Response and effectiveness

  • Fasenra starts working straight away. Significant reductions in blood eosinophil levels occur within 24 hours of Fasenra being administered. After 4 weeks, the number of asthma exacerbations reduced. A significant improvement in lung function was also observed 4 weeks after Fasenra was administered
  • Eosinophil cationic protein (ECP) levels are also significantly reduced after treatment with Fasenra. ECP is a protein found in eosinophils and is used as a measure of eosinophil activation. Activation of eosinophils can lead to the release of substances that promote inflammation.
  • Within 7 days of treatment with Fasenra, median peripheral blood eosinophil counts reached zero in patients with asthma enrolled in a phase II trial.
  • Phase III results also showed that treatment with Fasenra significantly improved exacerbation rates in patients with asthma, compared with those treated with a placebo. The improvement in exacerbation rates started to appear 4 weeks after administration with Fasenra, suggesting that it begins to have a beneficial effect shortly after patients start taking it. Results from a phase III trial also showed that Fasenra works quickly, improving lung function in as little as 4 weeks.
  • Patients with a baseline blood eosinophil count ≥300 cells/μL showed a numerically greater response than those with counts < 300 cells/μL.

7. Interactions

There have been no formal interaction studies conducted with Fasenra, according to the product information, and no interactions are documented.

You should refer to the prescribing information for Fasenra for any updates or newly noted interactions.


Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Fasenra only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2023 Revision date: March 28, 2023.