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Biologic — Anti-IL-5 Monoclonal Antibody Pregnancy: 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 foetus. There are limited 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 foetus is unknown. There are no data on excretion in human milk; mepolizumab was excreted into cynomolgus monkey milk at less than 0.5% of plasma concentrations. A decision must be made whether to discontinue breast-feeding or to discontinue therapy.

Mepolizumab (Eosinophilic GPA)

Brand names: Nucala

This is mepolizumab used in rheumatology for eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg–Strauss), given as a specialist-initiated subcutaneous injection to control eosinophilic vasculitic disease and reduce corticosteroid burden.

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: 300 mg (EGPA — eosinophilic granulomatosis with polyangiitis; adults and adolescents aged 12 years and older)
Route: Subcutaneous injection into the upper arm, thigh or abdomen; must be administered by a healthcare professional
Frequency: Once every 4 weeks
Fetched UK SPC: Nucala 100 mg powder for solution for injection (eMC product 1938). It is recommended that Nucala is prescribed by physicians experienced in the diagnosis and treatment of severe refractory eosinophilic asthma, CRSwNP, COPD, EGPA or HES. The 300 mg EGPA dose requires more than one injection; it is recommended that each injection is administered at least 5 cm apart. The powder should be reconstituted prior to administration and the reconstituted solution used immediately; each vial is for a single patient and any remainder discarded. Nucala is intended for long-term treatment — the need for continued therapy is to be reviewed at least on an annual basis as determined by physician assessment of disease severity and improvement of symptom control. Patients who develop life-threatening manifestations of EGPA must also be evaluated for the need for continued therapy, as Nucala has not been studied in that population. Other indications in the same SPC: severe eosinophilic asthma in adults and adolescents aged 12 years and older, 100 mg once every 4 weeks (children aged 6 to 11 years, 40 mg once every 4 weeks); CRSwNP in adults, 100 mg once every 4 weeks; COPD in adults, 100 mg once every 4 weeks; HES in adults, 300 mg once every 4 weeks. No dose adjustment is required for elderly patients aged 65 years and over. Paediatric EGPA (the SPC gives fixed weight-band doses, not a per-kg dose, so paedDose is null): 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; the posology in children and adolescents aged 6 to 17 years with EGPA was supported by modelling and simulation data. Safety and efficacy in EGPA have not been established in children below 6 years of age and no data are available. Verify any under-18 use against a children's formulary.

Dose adjustments

Renal

No dose adjustment is required in patients with renal or hepatic impairment.

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

Side effects

  • Headache (very common — 32% in the EGPA study)
  • Injection site reactions (15% in the EGPA study) and back pain (13% in the EGPA study)
  • Lower respiratory tract infection, urinary tract infection and pharyngitis (common)
  • Systemic allergic (hypersensitivity) reactions — common, reported by 4% of EGPA patients; anaphylaxis is rare
  • Nasal congestion (common)
  • Herpes zoster (common)

Interactions

  • Formal drug interaction trials have not been performed with mepolizumab (US labelling §7)

Clinical monograph

How it works

It is a monoclonal antibody against interleukin-5 (IL-5), reducing eosinophil production and survival that drive tissue damage in EGPA.

Prescribing in practice

  • Hypersensitivity reactions, including delayed systemic reactions, can occur and require monitoring after administration.
  • It is not a treatment for acute vasculitic flares, and existing immunosuppression or corticosteroids should not be stopped abruptly when starting it.
  • Parasitic (helminth) infection should be treated before initiation, as eosinophils contribute to host defence.

Monitoring

Monitor for hypersensitivity and injection-site reactions and for clinical disease control allowing corticosteroid tapering, in line with the SPC.

Counselling the patient

  • Report rash, swelling or breathing difficulty after an injection.
  • Do not stop your steroids suddenly; reduce only as advised.
  • Continue to report any return of vasculitis symptoms.

Evidence & guidelines

A randomised controlled trial in relapsing or refractory EGPA showed more accrued remission time and reduced oral corticosteroid use with mepolizumab.

Reference: NICE TA671; MIRRA Trial (NEJM 2017); EULAR EGPA Guidelines; SPC Nucala; 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).

Related

Curated clinical cross-links plus same-class fallbacks.