Disease-Modifying Therapy — MS (Interferon) Pregnancy: Avoid — associated with spontaneous abortion; discontinue before planned conception; switch to safer DMT

Interferon Beta-1a

Brand names: Avonex, Rebif

Adult dose

Dose: Avonex: 30 micrograms IM once weekly | Rebif: 22–44 micrograms SC 3x/week

Route: IM (Avonex) or SC (Rebif)

Frequency: Weekly (Avonex) or 3x weekly (Rebif)

Max: Avonex 30 micrograms/week; Rebif 44 micrograms 3x/week

Dose titration for Rebif: start 8.8 mcg 3x/week × 2 weeks → 22 mcg × 2 weeks → 44 mcg maintenance. Pre-medicate with ibuprofen or paracetamol to reduce flu-like side effects. Self-injection training required.

Paediatric dose

Route:

Seek specialist opinion — not licensed under 18 years

Dose adjustments

Renal

No dose adjustment required

Hepatic

Use with caution in severe hepatic impairment — monitor LFTs

Clinical pearls

Flu-like symptoms mitigated by evening injection and pre-/post-dose NSAIDs
Neutralising antibodies develop in ~20–30% on Rebif — consider switching if high-titre Ab with clinical breakthrough
First-line DMT option for relapsing MS with low-moderate disease activity
Less effective than natalizumab or alemtuzumab for highly active MS
Interferon-beta associated with worsening in neuromyelitis optica spectrum disorder (NMOSD) — contraindicated in this diagnosis

Contraindications

Severe depressive disorder or suicidal ideation
Decompensated hepatic failure
Hypersensitivity to natural or recombinant interferon beta
Pregnancy (relative — discuss risk/benefit)

Side effects

Flu-like syndrome (fever, myalgia, chills — most common, usually first 3 months)
Injection site reactions (SC formulations)
Elevated transaminases
Lymphopenia
Depression
Thyroid dysfunction
Neutralising antibodies (reduce efficacy)
Lipoatrophy at injection sites

Interactions

Additive myelosuppression with chemotherapy
Caution with hepatotoxic drugs
Monitor antiepileptic levels — interferons affect CYP450

Monitoring

LFTs and FBC at baseline, 1, 3, 6 months then 6-monthly
Thyroid function annually
Depression screening at each visit
Neutralising antibody titres at 12 and 24 months

Reference: BNFc; BNF 90; NICE TA32/TA127 (Interferons for MS); PRISMS Trial; MSCRG Trial. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways