Anti-IL-5 Monoclonal Antibody Pregnancy: There is a limited amount of data (fewer than 300 pregnancy outcomes) from use in pregnant women; mepolizumab crosses the placental barrier in monkeys and animal studies do not indicate reproductive toxicity, but the potential for harm to a human fetus is unknown. As a precautionary measure it is preferable to AVOID use during pregnancy; administration to pregnant women should only be considered if the expected benefit to the mother is greater than any possible risk to the fetus. Breast-feeding: no data on excretion in human milk (less than 0.5% of plasma concentrations in cynomolgus monkeys) - decide whether to discontinue breast-feeding or the medicine, taking benefits of each into account.

Mepolizumab

Brand names: Nucala

Mepolizumab is a humanised anti-interleukin-5 (IL-5) monoclonal antibody given by subcutaneous injection, used as add-on therapy for severe eosinophilic asthma and other eosinophil-driven conditions such as eosinophilic granulomatosis with polyangiitis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Severe eosinophilic asthma, adults and adolescents aged 12 years and older: 100 mg once every 4 weeks. Same dose (100 mg every 4 weeks) for CRSwNP in adults and for COPD in adults. EGPA, adults and adolescents aged 12 years and older: 300 mg once every 4 weeks. HES, adults: 300 mg once every 4 weeks.

Route: Subcutaneous injection only - must be administered by a healthcare professional; may be injected into the upper arm, thigh or abdomen. For doses requiring more than one injection, each injection should be at least 5 cm apart.

Frequency: Once every 4 weeks

Recommended that mepolizumab is prescribed by physicians experienced in the diagnosis and treatment of severe refractory eosinophilic asthma, CRSwNP, COPD, EGPA or HES. Intended for long-term treatment; the need for continued therapy is to be considered at least annually by physician assessment of disease severity and control of exacerbations. In CRSwNP, alternative treatments can be considered in patients showing no response after 24 weeks, though some patients with an initial partial response may improve with continued treatment beyond 24 weeks. Patients who develop life-threatening or organ-threatening manifestations of EGPA or HES must also be evaluated for the need for continued therapy, as the product has not been studied in these populations. Must NOT be used to treat acute asthma or COPD exacerbations; do not abruptly discontinue corticosteroids after initiation - reduce gradually under physician supervision. Pre-existing helminth infections should be treated before starting therapy. Contains polysorbate 80. The powder must be reconstituted before administration and the reconstituted solution used immediately; each vial is for a single patient. PAEDIATRIC (fixed mg doses by age and weight band - NO per-kg dose is stated): severe eosinophilic asthma, children aged 6 to 11 years, 40 mg subcutaneously once every 4 weeks. EGPA, children aged 6 to 11 years weighing 40 kg or more, 200 mg subcutaneously once every 4 weeks; children aged 6 to 11 years weighing less than 40 kg, 100 mg subcutaneously once every 4 weeks (posology in children and adolescents aged 6 to 17 years with EGPA was supported by modelling and simulation data). Safety and efficacy have not been established in children under 6 years for asthma or EGPA, under 18 years for CRSwNP or HES; there is no relevant use under 18 years for COPD. Verify paediatric dosing against a children's formulary. Product source: Nucala 100 mg powder for solution for injection.

Dose adjustments

Renal

No dose adjustment is required in patients with renal or hepatic impairment (section 4.2). No dose adjustment is required for elderly patients aged 65 years and older.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients listed in section 6.1

Side effects

Very common: headache (reported by 20% in severe eosinophilic asthma studies, 32% in the EGPA study)
Common: injection site reactions (8% in asthma studies, 15% in EGPA)
Common: back pain (6-13% across indications); arthralgia reported in 5% of COPD patients
Common: lower respiratory tract infection, urinary tract infection, pharyngitis, herpes zoster; nasal congestion
Common: hypersensitivity reactions (systemic allergic) - acute and delayed systemic reactions including urticaria, angioedema, rash, bronchospasm and hypotension have occurred, generally within hours of administration but sometimes delayed by several days and sometimes after long-duration treatment. Rare: anaphylaxis. The section 4.8 table was truncated at the source-fetch limit.

Interactions

No interaction studies have been performed. Cytochrome P450 enzymes, efflux pumps and protein-binding mechanisms are not involved in the clearance of mepolizumab, and the potential for interactions is considered low (section 4.5; text truncated at the source-fetch limit). US labelling agrees that no formal drug interaction trials have been performed.

Clinical monograph

How it works

It binds circulating IL-5 and prevents it from engaging its receptor on eosinophils, reducing eosinophil production and survival and thereby dampening eosinophilic airway inflammation.

Prescribing in practice

Not a treatment for acute bronchospasm or status asthmaticus and must never be used to relieve an acute asthma attack; patients should continue their usual reliever and controller therapy.
Reserved for severe eosinophilic asthma confirmed by blood eosinophil criteria and prescribed within specialist severe-asthma services per NICE guidance.
Treat any pre-existing helminth infection before starting, and consider hypersensitivity reactions which can occur during or after administration.

Monitoring

Monitor asthma control, exacerbation frequency and blood eosinophil count, and observe for hypersensitivity reactions after dosing.

Counselling the patient

This injection is added to your usual inhalers to prevent attacks, not to treat one that is happening now.
Keep using your reliever inhaler and seek urgent help if your breathing suddenly worsens.
Report any rash, swelling or breathing difficulty after an injection.

Evidence & guidelines

NICE technology appraisal guidance supports mepolizumab as add-on therapy for severe refractory eosinophilic asthma in defined populations.

Reference: MENSA Trial (Ortega et al, NEJM 2014); SIRIUS Trial (Bel et al, NEJM 2014); NICE TA339; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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