Anti-IL-5 Monoclonal Antibody Pregnancy: Limited data (<300 pregnancy outcomes); mepolizumab crosses the placenta in monkeys and potential harm to a human fetus is unknown — as a precaution it is preferable to avoid Nucala during pregnancy and use it only if the expected benefit to the mother outweighs any possible risk to the fetus. No human breast-milk data; decide whether to discontinue breast-feeding or therapy (§4.6).

Mepolizumab (CRSwNP)

Brand names: Nucala

Mepolizumab is a subcutaneous biologic used as add-on therapy for severe chronic rhinosinusitis with nasal polyps (CRSwNP) that remains inadequately controlled despite intranasal corticosteroids and where surgery and/or systemic steroids are otherwise required.

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: 100 mg

Route: Subcutaneous injection

Frequency: Once every 4 weeks

CRSwNP, adults: the recommended dose of mepolizumab is 100 mg administered subcutaneously once every 4 weeks (§4.2). Intended for long-term treatment; consideration can be given to alternative treatments in patients who have shown no response after 24 weeks, although some patients with an initial partial response may improve with continued treatment beyond 24 weeks. Safety and efficacy in CRSwNP below 18 years of age have not been established. Should be prescribed by physicians experienced in the diagnosis and treatment of severe refractory eosinophilic asthma, CRSwNP, COPD, EGPA or HES. Other indications in the same SPC: severe eosinophilic asthma — adults and adolescents 12 years and over 100 mg every 4 weeks, children 6 to 11 years 40 mg every 4 weeks; COPD adults 100 mg every 4 weeks; EGPA — adults and adolescents 12 years and older 300 mg every 4 weeks, children 6-11 years weighing at least 40 kg 200 mg every 4 weeks and weighing under 40 kg 100 mg every 4 weeks; HES adults 300 mg every 4 weeks. Administration: pre-filled pen or pre-filled syringe for subcutaneous injection only; self-administration possible if trained; recommended sites abdomen or thigh (upper arm if given by a caregiver); where more than one injection is required each injection should be at least 5 cm apart. Source product: Nucala 100 mg solution for injection in pre-filled pen (UK SPC); US label agrees on 100 mg every 4 weeks for CRSwNP.

Dose adjustments

Renal

No dose adjustment is required in patients with renal or hepatic impairment (§4.2).

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 (§4.3)

Side effects

Headache — very common; reported by 18% of CRSwNP patients (§4.8)
Back pain — reported by 7% of CRSwNP patients (§4.8)
Injection site reactions (§4.8)
Common infections: lower respiratory tract infection, urinary tract infection, pharyngitis, herpes zoster (§4.8)
Hypersensitivity (systemic allergic) reactions — common; anaphylaxis — rare (§4.8)
Nasal congestion — common (§4.8)

Interactions

No interaction studies have been performed; cytochrome P450 enzymes, efflux pumps and protein-binding mechanisms are not involved in the clearance of mepolizumab, so the potential for interactions is considered low (§4.5)

Clinical monograph

How it works

Mepolizumab is a humanised monoclonal antibody against interleukin-5 (IL-5); by blocking IL-5 binding to its receptor on eosinophils it reduces eosinophil production and survival, dampening the type-2 inflammation that drives polyp formation.

Prescribing in practice

Hypersensitivity and injection-site reactions can occur, so administer with appropriate observation and do not use to treat acute symptoms or exacerbations.
Pre-existing helminth infection should be treated before starting, as eosinophils contribute to host defence against parasites.
It is given by subcutaneous injection at regular intervals as add-on therapy and should be initiated and reviewed by a specialist within agreed access criteria.

Monitoring

Assess polyp size, nasal obstruction and symptom scores at defined review points to confirm continued benefit, and monitor for hypersensitivity reactions around administration.

Counselling the patient

This is an add-on treatment for nasal polyps, not a reliever for sudden symptoms.
Keep using your steroid nasal spray unless told otherwise.
Report any rash, swelling, breathing difficulty or signs of an allergic reaction after injection.

Evidence & guidelines

Mepolizumab is licensed for severe CRSwNP on the basis of randomised trials showing reduced polyp size and nasal obstruction, and is positioned by NICE for specialist add-on use.

Reference: SYNAPSE trial (Han et al. NEJM 2021); NICE TA662; MHRA SPC Nucala; Fokkens et al. EPOS 2020; 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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