How it is administered

Mepolizumab is given as a subcutaneous injection (under the skin). It is available in several forms:

• As a lyophilized powder in a vial that is reconstituted and administered by a healthcare professional.
• As a prefilled autoinjector or prefilled syringe for subcutaneous use. These are available in 100 mg/mL (for adults and adolescents) and 40 mg/0.4 mL (for children aged 6 to 11 years).

The injection is usually given in the upper arm, thigh, or abdomen. For certain conditions, such as hypereosinophilic syndrome (HES), the recommended dose is 300 mg every 4 weeks, given as three separate 100 mg injections at least 5 cm apart.

How it works

Mepolizumab is a monoclonal antibody that targets interleukin-5 (IL-5), a protein that plays a key role in the growth, activation, and survival of eosinophils (a type of white blood cell). By binding to IL-5, mepolizumab prevents it from attaching to its receptor on the surface of eosinophils. This blocks the action of IL-5 and reduces the number of eosinophils in the blood and tissues.

Eosinophils are involved in inflammation and are often elevated in certain diseases, including some blood cancers and hypereosinophilic syndromes. By lowering eosinophil levels, mepolizumab helps control symptoms and reduce disease activity. The reduction in eosinophil counts is usually seen within weeks of starting treatment and is maintained with regular dosing.

Who Should take it

Mepolizumab is indicated for:

• Add-on maintenance treatment of adults and children aged 6 years and older with severe asthma and an eosinophilic phenotype.
• Add-on maintenance treatment of adults with chronic rhinosinusitis with nasal polyps (CRSwNP).
• Add-on maintenance treatment of adults with chronic obstructive pulmonary disease (COPD) and an eosinophilic phenotype.
• Treatment of adults with eosinophilic granulomatosis with polyangiitis (EGPA).
• Treatment of adults and children aged 12 years and older with hypereosinophilic syndrome (HES) for at least 6 months without an identifiable non-hematologic secondary cause.

For blood cancers such as chronic eosinophilic leukemia, mepolizumab may be considered if the disease presents as a hypereosinophilic syndrome and other causes have been excluded.

Who should not take it

Mepolizumab should not be used in patients who have had a hypersensitivity reaction to mepolizumab or any of its ingredients. Signs of hypersensitivity can include rash, swelling, difficulty breathing, or low blood pressure after receiving the medication.

It is also not intended for the relief of acute asthma attacks, acute exacerbations of COPD, or other acute symptoms. Patients with active parasitic (helminth) infections should be treated for the infection before starting mepolizumab. If a parasitic infection occurs during treatment and does not respond to standard therapy, mepolizumab should be stopped until the infection resolves.

Commonly used with

Mepolizumab is often used in combination with other medications, depending on the condition:

• In asthma, it is added to inhaled corticosteroids and other controller medications.
• In hypereosinophilic syndrome, it may be used alongside corticosteroids, immunosuppressive agents, or cytotoxic therapies, especially if these alone are not adequately controlling symptoms.

Patients should not stop their other medications abruptly when starting mepolizumab. Any reduction in steroids should be done gradually under medical supervision.

Commonly tested with

In clinical trials, mepolizumab has been tested alongside standard background therapies for each condition:

• For asthma: with inhaled corticosteroids, long-acting beta agonists, and other controller medications.
• For hypereosinophilic syndrome: with stable doses of corticosteroids, immunosuppressives, or cytotoxic agents.

No formal drug interaction studies have been performed, but population data suggest that commonly used small molecule drugs do not affect mepolizumab exposure.