An anti-IL5 biologic injection
Mepolizumab
An add-on injection for severe eosinophilic asthma that reduces flare-ups by targeting a specific part of the immune system.
What is Mepolizumab?
Mepolizumab is a biologic 'add-on' injection used for severe asthma that is driven by high levels of eosinophils, a type of white blood cell. It blocks a messenger called interleukin-5 (IL-5) that those cells need, which lowers their number and reduces asthma flare-ups over time. It is given as an injection under the skin, usually at regular intervals, and is generally well tolerated. It is not a reliever inhaler and does not work quickly, so you must keep taking your usual asthma inhalers and treatments.
Education and reference only. This is a plain-language guide to Mepolizumab — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Mepolizumab is a biologic medicine, a type of laboratory-made antibody, used as an add-on treatment for severe asthma when eosinophils (a white blood cell linked to airway inflammation) are high despite usual inhalers. It is also used in some related conditions, such as certain types of nasal polyps, a blood vessel condition called eosinophilic granulomatosis with polyangiitis, and hypereosinophilic syndrome. It is given as an injection under the skin, sometimes by a nurse and sometimes self-administered after training.
How it works
Mepolizumab attaches to and blocks interleukin-5 (IL-5), a chemical messenger that eosinophils rely on to grow and survive. By neutralising IL-5, it gradually lowers the number of these inflammatory cells in the blood and airways, which reduces the swelling that triggers severe asthma attacks. The benefit builds up over weeks rather than working straight away, so it is an add-on to, not a replacement for, your regular inhalers.
Company & origin
Originated / developed by: GlaxoSmithKline.
A biologic 'add-on' injection used in the UK for severe asthma driven by high levels of a white blood cell called the eosinophil, and for some related conditions.
What it treats
Conditions Mepolizumab is used for
Practical use
How to take Mepolizumab
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given as an injection under the skin at regular intervals, either by a healthcare professional or by yourself or a carer after proper training.
- Keep using your regular asthma inhalers and follow your personal asthma action plan; this is an add-on, not a replacement.
- Do not use it as a reliever during an asthma attack, as it does not work quickly; use your rescue inhaler and seek help as advised.
- Try to keep to your scheduled injection dates so the benefit is maintained over time.
- Tell your specialist team if your asthma is not improving after a few months so they can review whether to continue.
Weighing it up
Advantages & disadvantages of Mepolizumab
Advantages
- Can substantially reduce severe asthma flare-ups in people with high eosinophil levels.
- May allow steroid tablets to be reduced in people who have needed them long term.
- Generally well tolerated and can be given as an injection under the skin, sometimes at home.
Disadvantages
- Works gradually over weeks and is not a quick-acting reliever.
- Only suitable for a specific type of severe asthma and must be started by a specialist.
- Can cause injection-site reactions and, rarely, allergic reactions.
Practical use
Good to know
Mepolizumab is reserved for severe asthma that stays poorly controlled despite high-dose inhaled treatment, and it is started and supervised by a specialist team. The key thing to understand is that it is a preventer-type treatment that works over weeks to cut down flare-ups; it is not a rescue medicine, so you must keep your reliever inhaler to hand and continue your usual asthma plan unless your specialist changes it. It is generally well tolerated, with injection-site reactions and headache being the most common effects. As it dampens part of the immune system, your team may check for and treat any parasitic infection before starting, and you should report signs of infection. Allergic reactions are uncommon but possible, so the first injections may be watched.
Who should not take it / use with caution
- People who have had a serious allergic reaction to mepolizumab should not have it again.
- It is used cautiously where a parasitic (worm) infection is present, which is usually treated first.
- Anyone with an active untreated infection should discuss timing with their specialist before starting.
Monitoring
- Reviewing asthma control, flare-up frequency and eosinophil levels to judge whether it is helping.
- Checking for and treating any parasitic infection before and during treatment.
- Watching for allergic reactions, especially around the early injections.
Side effects
- Injection-site reactions, headache and back pain are among the more common effects.
- Some people get sore throat, eczema or cold-like symptoms.
- Rarely, allergic reactions can occur, so the first injections may be observed.
Key interactions
- It is not known to have the typical drug interactions of tablets, but tell your team about all your medicines.
- Live vaccines should be discussed with your specialist, as your immune response may be affected.
- If you also take long-term steroids, these should only be reduced gradually and under medical guidance.
Available as: Injection given under the skin (prefilled pen, prefilled syringe or vial), at regular intervals.
Answers
Mepolizumab: frequently asked questions
Is mepolizumab a steroid?
No. It is a biologic antibody that blocks a messenger called IL-5; it is not a steroid, though it may help some people reduce the steroid tablets they need.
Can I stop my inhalers once I start it?
No. Mepolizumab is an add-on treatment and works slowly, so you must keep using your regular inhalers and your asthma action plan unless your specialist advises otherwise.
How quickly will it work?
It works gradually over weeks by lowering inflammatory cells, so it is not a rescue treatment; your specialist will review whether it is helping after a few months.
Can I inject it at home?
Many people or their carers can give the injection at home after proper training; your team will show you how and supply the right device.
Is it safe to have vaccinations?
Most vaccines are fine, but check with your specialist about live vaccines, as your immune response may be affected.
The wider class
About Anti-IL5 biologic (severe eosinophilic asthma)
Mepolizumab belongs to the anti-il5 biologic (severe eosinophilic asthma) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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