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Interferon (immunomodulator) Pregnancy: A large amount of data (more than 1000 pregnancy outcomes) from registries and post-marketing experience indicates no increased risk of major congenital anomalies after pre-conception exposure to interferon beta or exposure during the first trimester; experience with second- and third-trimester exposure is very limited. Based on animal data there is a possibly increased risk of spontaneous abortion, although the currently available human data do not suggest an increased risk so far. 'If clinically needed, the use of Avonex may be considered during pregnancy.' Breast-feeding: levels of interferon beta-1a excreted in human milk are expected to be negligible, no harmful effects on the breastfed newborn/infant are anticipated, and 'Avonex can be used during breast-feeding'. Fertility: at very high doses, anovulatory and abortifacient effects were observed with a related form of interferon beta-1a in rhesus monkeys; no information is available on male fertility. (Product-specific — AVONEX §4.6.)

Interferon beta

Brand names: Avonex, Rebif, Betaferon, Plegridy, Extavia

Interferon beta is an immunomodulatory protein used as a disease-modifying therapy in relapsing forms of multiple sclerosis.

Adult dose

Dose: AVONEX (interferon beta-1a) ONLY — relapsing multiple sclerosis in adults: 30 micrograms (0.5 mL solution) by intramuscular (IM) injection once a week. Optional titration at initiation, to reduce the incidence and severity of flu-like symptoms: begin at quarter-dose increments per week, reaching the full dose (30 micrograms/week) by the fourth week; alternatively begin at approximately a half dose once a week before increasing to the full dose. In order to obtain adequate efficacy, 30 micrograms once a week should be reached and maintained after the titration period. SCOPE: this figure is taken from the AVONEX SPC alone. The other interferon beta products named on this page — Rebif, Betaferon, Plegridy and Extavia — are different products with different active substances, routes, strengths and schedules, and NONE of them is covered by this source; use each product's own SPC for its dose.
Route: IM — intramuscular injection; the injection site should be varied each week. A 25 mm, 25 gauge needle may be prescribed to patients for whom such a needle is appropriate (§4.2).
Frequency: Once a week
SCOPE OF THIS ENTRY: AVONEX 30 micrograms/0.5 ml solution for injection (eMC product 886) only — see the scope sentence in the dose. LICENSED INDICATIONS (§4.1), adults: patients diagnosed with relapsing multiple sclerosis (in clinical trials characterised by two or more relapses in the previous three years without continuous progression between relapses); and patients with a single demyelinating event with an active inflammatory process, if severe enough to warrant treatment with intravenous corticosteroids, if alternative diagnoses have been excluded, and if they are determined to be at high risk of developing clinically definite multiple sclerosis. 'AVONEX should be discontinued in patients who develop progressive MS.' NO MAXIMUM DOSE IS RECORDED: §4.2 prints no ceiling. It states only that 'No additional benefit has been shown by administering a higher dose (60 micrograms) once a week' — that is a statement about added benefit, not a licensed maximum, so 60 micrograms has deliberately NOT been entered as maxDose. INITIATION: treatment should be initiated under the supervision of a physician experienced in the treatment of the disease. FLU-LIKE SYMPTOMS: an antipyretic analgesic is advised prior to injection and for an additional 24 hours after each injection; these symptoms are usually present during the first few months of treatment. DURATION: it is not known for how long patients should be treated; patients should be clinically evaluated after two years and longer-term treatment decided on an individual basis; treatment should be discontinued if the patient develops chronic progressive MS. ELDERLY: clinical studies did not include sufficient patients aged 65 and over, but based on the mode of clearance of the active substance there are no theoretical reasons for any requirement for dose adjustment. PAEDIATRIC (§4.2): safety and efficacy in children and adolescents aged 10 to 18 years 'have not yet been fully established' and 'no recommendation on a posology can be made'; safety and efficacy below 10 years of age have not been established and no data are available. paedDose is therefore null — verify any under-18 use against a children's formulary. Some sections of the product information we used were incomplete — check the full SPC. The US label in this bundle (openFDA — Betaseron, interferon beta-1b, subcutaneous, alternate-day) was NOT used for any figure: it is a different active substance, route and schedule.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • History of hypersensitivity to natural or recombinant interferon beta or to any of the excipients listed in section 6.1 (UK SPC §4.3)
  • Patients with current severe depression and/or suicidal ideation (UK SPC §4.3)

Side effects

  • Flu-like symptoms — the highest incidence of adverse reactions; most commonly myalgia, fever, chills, sweating, asthenia, headache and nausea; most prominent at initiation of therapy and decreasing in frequency with continued treatment. Titration at initiation has demonstrated a reduction in their severity and incidence
  • Headache (very common)
  • Common: muscle spasticity, hypoesthesia, vomiting, diarrhoea, nausea, rhinorrhoea
  • Laboratory abnormalities (common): lymphocyte count, white blood cell count, neutrophil count and haematocrit decreased; blood potassium and blood urea nitrogen increased. Uncommon: platelet count decreased
  • Transient neurological symptoms that may mimic MS exacerbations, including transient episodes of hypertonia and/or severe muscular weakness that prevent voluntary movements; temporally related to the injections and may recur after subsequent injections
  • Rare / not known: thrombotic microangiopathy including thrombotic thrombocytopenic purpura / haemolytic uraemic syndrome, pancytopenia, thrombocytopenia, cardiomyopathy, congestive heart failure, palpitations, arrhythmia, tachycardia, seizures, syncope, dizziness, paraesthesia, migraine, dyspnoea, pulmonary arterial hypertension, abnormal liver function tests, weight decreased or increased
  • Injection site necrosis has been reported in post-marketing experience (§4.4)
  • ⚠️ §4.8 of this bundle is truncated at the source-fetch limit (it ends part-way through 'Skin and…'), so this list is incomplete — read the full §4.8 on the eMC before relying on it

Interactions

  • Anti-epileptics / history of seizures: AVONEX should be administered with caution to patients with a history of seizures and to those receiving treatment with anti-epileptics, particularly if their epilepsy is not adequately controlled (§4.4)
  • Other medicinal products associated with hepatic injury (including alcohol): hepatic injury has been reported with interferon beta, in some cases in the presence of other hepatotoxic products; the potential for additive effects has not been determined — exercise caution on concomitant use (§4.4)
  • ⚠️ §4.5 (interactions) is not separately captured by the fetcher; its text is absorbed into the warnings section, and that section is truncated in this bundle — read §4.5 on the eMC directly

Monitoring

  • In addition to the laboratory tests normally required for monitoring patients with MS, complete and differential white blood cell counts, platelet counts, and blood chemistry including liver function tests are recommended during AVONEX therapy (§4.4)
  • Patients with myelosuppression may require more intensive monitoring of complete blood cell counts, with differential and platelet counts (§4.4)
  • Depression and suicidal ideation: patients should be advised to report symptoms immediately; patients exhibiting depression should be monitored closely during therapy and treated appropriately, and cessation of therapy considered (§4.4)
  • Signs of hepatic injury — elevated serum hepatic enzymes, hepatitis, autoimmune hepatitis and hepatic failure have been reported (§4.4)
  • Thrombotic microangiopathy: if clinical features are observed (thrombocytopenia, new onset hypertension, fever, CNS symptoms, impaired renal function), further testing of blood platelet levels, serum LDH, blood films and renal function is recommended; if diagnosed, prompt treatment and immediate discontinuation are recommended (§4.4)
  • Nephrotic syndrome: periodic monitoring of early signs or symptoms — e.g. oedema, proteinuria and impaired renal function — is recommended, especially in patients at higher risk of renal disease (§4.4)
  • Patients with cardiac disease (angina, congestive heart failure, arrhythmia) should be closely monitored for worsening of their clinical condition (§4.4)
  • Close monitoring should be considered in severe renal and hepatic failure and in severe myelosuppression (§4.4)
  • Injection sites: advise aseptic technique and rotation of sites with each dose; review the self-administration procedure periodically, especially if injection site reactions have occurred (§4.4)

Clinical monograph

How it works

It modulates immune activity by reducing pro-inflammatory cytokine production, limiting T-cell activation and trafficking across the blood-brain barrier, thereby reducing central nervous system inflammation.

Prescribing in practice

  • Hepatic injury can occur, so check liver function before and during treatment and review if transaminases rise or jaundice develops.
  • Flu-like symptoms are common at initiation and can be mitigated with gradual dose escalation and supportive measures.
  • Use with caution in those with depression and a history of seizures, monitoring mental state during treatment.

Monitoring

Monitor full blood count, liver function and thyroid function periodically during therapy.

Counselling the patient

  • Rotate injection sites and report persistent redness, pain or skin breakdown.
  • Flu-like symptoms often ease after the first weeks of treatment.
  • Seek advice if you notice low mood, yellowing of the skin or unusual bruising.

Evidence & guidelines

Interferon beta is an established first-line disease-modifying therapy for relapsing multiple sclerosis, reducing relapse rate and MRI lesion activity.

Reference: NICE NG220; ABN MS guidelines; 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.

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