Section 04 · Monograph

Peginterferon beta-1a

Reviewed Nov 2026FDA label

PlegridyInterferon (pegylated)

Indications

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

The mechanism by which Plegridy exerts its effects in MS patients is unknown, per FDA labeling
Peginterferon beta-1a is formed by covalent conjugation of a single 20 kDa methoxy poly(ethylene glycol) (mPEG) moiety to interferon beta-1a, which extends its half-life relative to non-pegylated interferon beta-1a, allowing less frequent (every-14-day) dosing
Interferon beta-1a is produced by recombinant DNA technology in Chinese hamster ovary cells and shares the amino acid sequence of natural human interferon beta

Maintenance dose: 125 mcg subcutaneously (or intramuscularly) every 14 days
Titration using starter pack: Day 1 = 63 mcg (orange, first dose); Day 15 = 94 mcg (blue, second dose); Day 29 onward = 125 mcg (grey) every 14 days
Subcutaneous injection sites: abdomen, back of upper arm, or thigh; intramuscular sites: left or right thigh
Allow prefilled pen/syringe to reach room temperature (~30 minutes) before injection; rotate injection sites with each dose
Prophylactic analgesics/antipyretics on and around injection days may help reduce flu-like symptoms

History of hypersensitivity to natural or recombinant interferon beta or peginterferon, or to any other component of the formulation
Intramuscular prefilled syringe presentation contains natural rubber latex in the needle cover — contraindicated (route) in latex-sensitive individuals

The Plegridy prescribing information does not contain a specific drug-drug interaction section; no formal interaction studies are described
Use caution with concomitant hepatotoxic agents given the risk of hepatic injury

Injection site erythema — very common (62% vs 7% placebo in trials); overall injection site reactions in 66% vs 11% placebo, severe reactions in 3%; injection site necrosis reported rarely (1 of 1468 patients)
Influenza-like illness — common (47% vs 13% placebo); less than 1% discontinued due to this
Pyrexia (45% vs 15% placebo), headache (44% vs 33%), myalgia (19% vs 6%), chills, asthenia, arthralgia
Hepatic injury — elevated transaminases (6% vs 3% placebo); rare hepatic failure reported with interferon beta products
Depression and suicidal ideation — reported (8% in both Plegridy and placebo groups in trials, per label); patients must report symptoms immediately
Decreased white blood cell count (7% vs 1% placebo); severe thrombocytopenia and neutropenia in <1% each
Anaphylaxis and serious allergic reactions (angioedema, urticaria) — <1% of patients; postmarketing anaphylaxis reported
Thrombotic microangiopathy (TMA), including TTP/HUS, sometimes fatal
Pulmonary arterial hypertension (PAH)
Seizures (<1% incidence, similar to placebo in trials)
Autoimmune disorders (thrombocytopenia, thyroid dysfunction, autoimmune hepatitis) — <1% in both groups
Immunogenicity — <1% developed neutralizing antibodies to interferon beta-1a after 1 year; ~7% developed antibodies to PEG

Liver function tests at baseline and periodically during treatment; assess for jaundice, nausea, anorexia, dark urine
Mental health assessment for depression and suicidal ideation throughout treatment
Complete blood counts (WBC, neutrophils, platelets, lymphocytes) at baseline and periodically, especially in patients with myelosuppression
Cardiac assessment in patients with significant pre-existing cardiac disease
Injection site assessment at time of injection and periodically thereafter for erythema, pain, or necrosis
Renal function monitoring in patients with severe renal impairment
Monitor for signs/symptoms of TMA and PAH (unexplained dyspnea, fatigue) throughout treatment

Pregnancy: a large Nordic cohort study of 2,831 pregnancies exposed to interferon beta products found no evidence of increased risk of major birth defects
Some smaller studies suggested possible decreased birth weight or increased miscarriage risk with interferon beta exposure, but this was not confirmed in larger studies
Animal studies in monkeys showed abortifacient activity following repeat dosing at clinically relevant exposures
Advise patients of childbearing potential to notify their healthcare provider if pregnancy occurs or is planned during treatment
Lactation: limited published literature describes low levels of interferon beta-1a products in human milk; no data on effects on milk production; weigh developmental/health benefits of breastfeeding against potential infant exposure