Section 04 · Monograph

Interferon beta-1b

Reviewed Nov 2026FDA label

Betaseron / ExtaviaInterferon

Indications

Treatment of relapsing forms of multiple sclerosis (MS) in adults, including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease (Betaseron and Extavia)FDA-labeled

The mechanism of action of interferon beta-1b (Betaseron) in MS patients is unknown, per FDA labeling
Interferon beta-1b is a non-glycosylated form of human interferon beta produced by recombinant DNA technology in E. coli, differing slightly from natural interferon beta (serine substituted for cysteine at position 17)
Interferon beta-1b binds to specific cell-surface receptors, triggering intracellular signaling believed to underlie its immunomodulatory effects in MS

Maintenance dose: 0.25 mg (8 million IU) subcutaneously every other day
Titration over 6 weeks: Weeks 1-2 = 0.0625 mg (25% of full dose); Weeks 3-4 = 0.125 mg (50%); Weeks 5-6 = 0.1875 mg (75%); Week 7 onward = 0.25 mg (100%)
Reconstitute lyophilized powder with the supplied 1.2 mL diluent (0.54% sodium chloride); use within 3 hours if refrigerated; do not freeze
If a dose is missed, take as soon as remembered but maintain at least 48 hours between injections; do not inject on consecutive days
Rotate subcutaneous injection sites with each dose

History of hypersensitivity to natural or recombinant interferon beta, Albumin (Human), or any other component of the formulation

No formal drug interaction studies have been conducted with Betaseron, per FDA labeling
Use caution with concomitant hepatotoxic agents given risk of hepatic injury

Injection site reactions — very common (78% vs 26% placebo); injection site necrosis in 4% (0% placebo), typically within the first 4 months of therapy, sometimes requiring surgical debridement or skin grafting
Flu-like symptom complex (57% vs 37% placebo) — chills, fever, myalgia; median duration ~7.5 days, decreasing over time
Lymphopenia (86% vs 66% placebo), leukopenia (18% vs 6% placebo), neutropenia; ANC <1500/mm3 in 13% (vs 5% placebo)
Hepatic injury — elevated transaminases (SGPT >5x baseline in 12% vs 4% placebo); rare hepatic failure including autoimmune hepatitis
Depression and suicidality — increased frequency versus placebo; in trials, 3 suicides/8 attempts among 1,532 Betaseron patients vs 1 suicide/4 attempts among 965 placebo patients
Headache (50% vs 43%), hypertonia, pain, rash, insomnia, asthenia, abdominal pain, myalgia
Anaphylaxis and hypersensitivity reactions (dyspnea, bronchospasm, tongue edema, rash, urticaria) — rare
Seizures — temporally associated with beta interferon use
Cardiac events — cardiomyopathy, congestive heart failure reported without other known etiology
Thrombotic microangiopathy (TMA), including TTP/HUS, sometimes fatal
Pulmonary arterial hypertension (PAH), sometimes years after initiation
Drug-induced lupus erythematosus
Neutralizing antibody formation in up to 45% of patients in one study; clinical significance unclear
Rare fatal capillary leak syndrome reported postmarketing in patients with pre-existing monoclonal gammopathy

Complete blood count with differential, platelet count, and blood chemistries including liver function tests at 1, 3, and 6 months after starting therapy, then periodically thereafter
Monitor for new or worsening depression and suicidal ideation
Inspect injection sites regularly for erythema, swelling, or necrosis; rotate sites and avoid affected areas until fully healed
Cardiac monitoring in patients with pre-existing congestive heart failure
Monitor for signs of TMA, PAH, and drug-induced lupus throughout treatment
Thyroid function testing as clinically indicated

Pregnancy: no well-controlled studies in pregnant women; available observational data have not shown an increased risk of major birth defects with interferon beta exposure
Animal studies in monkeys showed dose-dependent increases in fetal loss at doses ≥3x the human therapeutic exposure
Background risks cited in labeling: major birth defects 2-4%, miscarriage 15-20% of clinically recognized pregnancies
Lactation: no data are available on the presence of Betaseron in human milk, effects on the breastfed infant, or effects on milk production; weigh developmental/health benefits of breastfeeding against potential infant risk and maternal need for therapy