Peginterferon Beta-1a is a prescription medicine (Interferon beta). The sections below reproduce one FDA label for it, named under "Label". Products in other forms, strengths or from other makers have their own labels, which can differ.
- Type
- Prescription only (Rx)
- Brand names
- Plegridy, Plegridy Pen
- Drug class
- Interferon beta
- Taken
- Subcutaneous, Intramuscular
- Label
- Biogen Inc., revised November 12, 2025 · full label on DailyMed
- Biosimilars
- None approved · details
What it is used for
PLEGRIDY is indicated for the treatment of relapsing forms of multiple sclerosis (MS), to include clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease, in adults. PLEGRIDY is an interferon beta indicated for the treatment of relapsing forms of multiple sclerosis (MS), to include clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease, in adults ( 1 )
Forms and strengths
PLEGRIDY is a clear to slightly opalescent and colorless to slightly yellow solution. Subcutaneous Administration: Injection: 125 mcg/0.5 mL in a single-dose prefilled pen or single-dose prefilled syringe ( 3 ) Injection: 63 mcg/0.5 mL in a single-dose prefilled pen or single-dose prefilled syringe ( 3 ) Injection: 94 mcg/0.5 mL in a single-dose prefilled pen or single-dose prefilled syringe ( 3 ) Intramuscular Administration: Injection: 125 mcg/0.5 mL solution in a single-dose prefilled syringe ( 3 ) Subcutaneous Administration: Injection: 125 mcg/0.5 mL in a single-dose prefilled pen or single-dose prefilled syringe Injection: 63 mcg/0.5 mL in a single-dose prefilled pen or a single-dose prefilled syringe Injection: 94 mcg/0.5 mL in a single-dose prefilled pen or a single-dose prefilled syringe Intramuscular Administration: Injection: 125 mcg/0.5 mL in a single-dose prefilled syringe
Who should not take it (contraindications)
PLEGRIDY is contraindicated in patients with a history of hypersensitivity to natural or recombinant interferon beta or peginterferon, or any other component of PLEGRIDY [see Warnings and Precautions ( 5.3 )] . History of hypersensitivity to natural or recombinant interferon beta or peginterferon, or any other component of PLEGRIDY ( 4 )
Warnings and precautions
Hepatic injury: monitor liver function tests; monitor patients for signs and symptoms of hepatic injury; consider discontinuation of PLEGRIDY if hepatic injury occurs ( 5.1 ) Depression and suicide: advise patients to report immediately any symptom of depression or suicidal ideation to their healthcare provider; consider discontinuation of PLEGRIDY if depression occurs ( 5.2 ) Anaphylaxis and other allergic reactions: Discontinue PLEGRIDY if a serious allergic reaction occurs ( 5.3 ) Injection site reactions: Do not administer PLEGRIDY into affected area until fully healed; if multiple lesions occur, change injection site or discontinue PLEGRIDY until healing of skin lesions ( 5.4 ) Congestive heart failure: monitor patients with pre-existing significant cardiac disease for worsening of cardiac symptoms ( 5.5 ) Decreased peripheral blood counts: monitor complete blood counts ( 5.6 ) Thrombotic Microangiopathy: Cases of thrombotic microangiopathy have been reported with interferon beta products. Discontinue PLEGRIDY if clinical symptoms and laboratory findings consistent with TMA occur ( 5.7 ) Pulmonary Arterial Hypertension: Cases of pulmonary arterial hypertension (PAH) have been reported in patients treated with interferon beta products, including PLEGRIDY. Discontinue PLEGRIDY if PAH is diagnosed ( 5.8 ) Autoimmune disorders: consider discontinuation of PLEGRIDY if a new autoimmune disorder occurs ( 5.9 )
5.1 Hepatic Injury Severe hepatic injury, including hepatitis, autoimmune hepatitis, and rare cases of severe hepatic failure, have been reported with interferon beta. Asymptomatic elevation of hepatic transaminases has also been reported, and in some patients has recurred upon rechallenge with interferon beta. Elevations in hepatic enzymes and hepatic injury have been observed with the use of PLEGRIDY in clinical studies. The incidence of increases in hepatic transaminases was greater in patients taking PLEGRIDY than in those taking placebo. The incidence of elevations of alanine aminotransferase above 5 times the upper limit of normal was 1% in placebo-treated patients and 2% in PLEGRIDY-treated patients. The incidence of elevations of aspartate aminotransferase above 5 times the upper limit of normal was less than 1% in placebo-treated patients and less than 1% in PLEGRIDY-treated patients. Elevations of serum hepatic transaminases combined with elevated bilirubin occurred in 2 patients. Both cases resolved following discontinuation of PLEGRIDY. Cases of noninfectious hepatitis have been reported in the postmarketing setting with use of PLEGRIDY. Monitor patients for signs and symptoms of hepatic injury.
5.2 Depression and Suicide Depression, suicidal ideation, and suicide occur more frequently in patients receiving interferon beta than in patients receiving placebo. In clinical studies, the overall incidence of adverse events related to depression and suicidal ideation in multiple sclerosis patients was 8% in both the PLEGRIDY and placebo groups. The incidence of serious events related to depression and suicidal ideation was similar and less than 1% in both groups. Advise patients to report immediately any symptom of depression or suicidal ideation to their healthcare provider. If a patient develops depression or other severe psychiatric symptoms, consider stopping treatment with PLEGRIDY.
5.3 Anaphylaxis and Other Allergic Reactions Serious allergic reactions are rare complications of treatment with interferon beta; anaphylaxis has been reported with use of PLEGRIDY in the postmarketing setting. Less than 1% of PLEGRIDY-treated patients experienced a serious allergic reaction such as angioedema or urticaria. Those who did have serious allergic reactions recovered promptly after treatment with antihistamines or corticosteroids. Discontinue PLEGRIDY if a serious allergic reaction occurs. The protective rubber cover of the PLEGRIDY prefilled syringe for intramuscular administration contains natural rubber latex which may cause allergic reactions and should not be handled by latex-sensitive individuals. The safe use of PLEGRIDY prefilled syringe in latex-sensitive individuals has not been studied.
5.4 Injection Site Reactions Including Necrosis Injection site reactions, including injection site necrosis, can occur with the use of interferon beta, including PLEGRIDY. In clinical studies of subcutaneous PLEGRIDY, the incidence of injection site reactions (e.g., injection site erythema, pain, pruritus, or edema) was 66% in the PLEGRIDY group and 11% in the placebo group; the incidence of severe injection site reactions was 3% in the PLEGRIDY group and 0% in the placebo group. One patient out of 1468 patients who received PLEGRIDY in clinical studies experienced injection site necrosis. The injury resolved with standard medical treatment. In Study 3, which compared single doses of intramuscular and subcutaneous PLEGRIDY [see Adverse Reactions ( 6.1 )] , the incidence of injection site reactions (e.g., injection site erythema, pain, pruritus, or edema) was 14% in the intramuscular PLEGRIDY group and 32% in the subcutaneous PLEGRIDY group. Injection site abscesses and cellulitis have been reported in the postmarketing setting with use of interferon beta. Some cases required treatment with hospitalization for surgical drainage and intravenous antibiotics. Periodically evaluate patient understanding and use of aseptic self-injection techniques and procedures, particularly if injection site necrosis has occurred. Decisions to discontinue therapy following necrosis at a single injection site should be based on the extent of the necrosis. For patients who continue therapy with PLEGRIDY after injection site necrosis has occurred, avoid administration of PLEGRIDY near the affected area until it is fully healed. If multiple lesions occur, change injection site or discontinue PLEGRIDY until healing occurs.
5.5 Congestive Heart Failure Congestive heart failure, cardiomyopathy, and cardiomyopathy with congestive heart failure occur in patients receiving interferon beta. In clinical studies, the incidence of cardiovascular events was 7% in both PLEGRIDY and placebo treatment groups. No serious cardiovascular events were reported in the PLEGRIDY group. Monitor patients with significant cardiac disease for worsening of their cardiac condition during initiation and continuation of treatment with PLEGRIDY.
5.6 Decreased Peripheral Blood Counts Interferon beta can cause decreased peripheral blood counts in all cell lines, including rare instances of pancytopenia and severe thrombocytopenia. In clinical studies, decreases in white blood cell counts below 3.0 x 10 9 /L occurred in 7% of patients receiving PLEGRIDY and in 1% receiving placebo. There is no apparent association between decreases in white blood cell counts and an increased risk of infections or serious infections. The incidence of clinically significant decreases in lymphocyte counts (below 0.5 x 10 9 /L), neutrophil counts (below 1.0 x 10 9 /L), and platelet counts (below 100 x 10 9 /L) were all less than 1% and similar in both placebo and PLEGRIDY groups. Two serious cases were reported in patients treated with PLEGRIDY: one patient (less than 1%) experienced severe thrombocytopenia (defined as a platelet count less than or equal to 10 x 10 9 /L), and another patient (less than 1%) experienced severe neutropenia (defined as a neutrophil count less than or equal to 0.5 x 10 9 /L). In both patients, cell counts recovered after discontinuation of PLEGRIDY. Compared to placebo, there were no significant differences in red blood cell counts in patients treated with PLEGRIDY. Monitor patients for infections, bleeding, and symptoms of anemia. Monitor complete blood cell counts, differential white blood cell counts, and platelet counts during treatment with PLEGRIDY. Patients with myelosuppression may require more intensive monitoring of blood cell counts. […]
Side effects (adverse reactions)
The following serious adverse reactions are discussed in more detail in other sections of labeling: Hepatic Injury [see Warnings and Precautions ( 5.1 )] Depression and Suicide [see Warnings and Precautions ( 5.2 )] Anaphylaxis and Other Allergic Reactions [see Warnings and Precautions ( 5.3 )] Injection Site Reactions Including Necrosis [see Warnings and Precautions ( 5.4 )] Congestive Heart Failure [see Warnings and Precautions (Section 5.5 )] Decreased Peripheral Blood Counts [see Warnings and Precautions ( 5.6 )] Thrombotic Microangiopathy [see Warnings and Precautions ( 5.7 )] Pulmonary Arterial Hypertension [see Warnings and Precautions ( 5.8 )] Autoimmune Disorders [see Warnings and Precautions ( 5.9 )] Seizures [see Warnings and Precautions ( 5.10 )] The most common adverse reactions in clinical trials of subcutaneous PLEGRIDY (incidence ≥10% and at least 2% more frequent on PLEGRIDY than on placebo) were injection site erythema, influenza-like illness, pyrexia, headache, myalgia, chills, injection site pain, asthenia, injection site pruritus, and arthralgia ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Biogen at 1-800-456-2255 or FDA at 1-800-FDA-1088 or http://www.fda.gov/medwatch.
6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of PLEGRIDY cannot be directly compared to rates in clinical trials of other drugs and may not reflect the rates observed in practice. PLEGRIDY Via Subcutaneous Administration In clinical studies (Study 1 and Study 2), a total of 1468 patients with relapsing multiple sclerosis received PLEGRIDY by subcutaneous injection for up to 177 weeks (41 months), with an overall exposure equivalent to 1932 person-years. A total of 1093 patients received at least 1 year, and 415 patients at least 2 years of treatment with PLEGRIDY. A total of 512 and 500 patients, respectively, received PLEGRIDY 125 micrograms every 14 days or every 28 days during the placebo-controlled phase of Study 1 (year 1). The experience in year 2 of Study 1 and in the 2-year safety extension study (Study 2) was consistent with the experience in the 1-year placebo-controlled phase of Study 1. In the placebo-controlled phase of Study 1, the most common adverse drug reactions for PLEGRIDY 125 micrograms subcutaneously every 14 days were injection site erythema, influenza-like illness, pyrexia, headache, myalgia, chills, injection site pain, asthenia, injection site pruritus, and arthralgia (all had incidence more than 10% and at least 2% more than placebo). The most commonly reported adverse event leading to discontinuation in patients treated with PLEGRIDY 125 micrograms subcutaneously every 14 days was influenza-like illness (in less than 1% of patients). Table 3 summarizes adverse reactions reported over 48 weeks from patients treated in the placebo-controlled phase of Study 1 who received subcutaneous PLEGRIDY 125 micrograms (n=512), or placebo (n=500), every 14 days. Table 3: Adverse Reactions in the 48-Week Placebo-Controlled Phase of Study 1 with an Incidence 2% Higher for PLEGRIDY Than for Placebo PLEGRIDY (N=512) % Placebo (N=500) % Nervous System Disorders Headache 44 33 Gastrointestinal Disorders Nausea 9 6 Vomiting 5 2 Musculoskeletal and Connective Tissue Disorders Myalgia 19 6 Arthralgia 11 7 General Disorders and Administration Site Conditions Injection site erythema 62 7 Influenza like illness 47 13 Pyrexia 45 15 Chills 17 5 Injection site pain 15 3 Asthenia 13 8 Injection site pruritus 13 1 Hyperthermia 4 1 Pain 5 3 Injection site edema 3 0 Injection site warmth 3 0 Injection site hematoma 3 1 Injection site rash 2 0 Investigations Body temperature increased 6 3 Alanine aminotransferase increased 6 3 Aspartate aminotransferase increased 4 2 Gamma-glutamyl-transferase increased 3 1 Skin and Subcutaneous Tissue Disorder Pruritus 4 1 Flu-Like Symptoms Influenza-like illness was experienced by 47% of patients receiving PLEGRIDY 125 micrograms every 14 days and 13% of patients receiving placebo. Fewer than 1% of PLEGRIDY-treated patients in Study 1 discontinued treatment due to flu-like symptoms. Comparison Between Subcutaneous and Intramuscular Administration An open-label, crossover study analyzed findings from 130 healthy volunteers to assess the bioequivalence of single doses of 125 micrograms of PLEGRIDY administered as a subcutaneous and intramuscular injection (Study 3). The most commonly reported adverse reactions (with >10% incidence in either arm) across both treatment periods were chills (36% in IM vs 27% in SC), pain (22% in IM vs 14% in SC), headache (36% in IM vs 41% in SC), injection site pain (11% in IM vs 15% in SC), and injection site erythema (2% in IM vs 25% in SC). Overall, injection site reactions were reported in 14% via IM route as compared to 32% via SC route.
6.2 Immunogenicity As with all therapeutic proteins, there is a potential for immunogenicity. The detection of antibody formation is highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies in the studies described below with the incidence of antibodies in other studies or to other interferon beta-1a products may be misleading. In Study 1, fewer than 1% of patients treated with PLEGRIDY SC every 14 days for 1 year developed neutralizing antibodies. Approximately 7% of PLEGRIDY SC-treated patients developed antibodies to the polyethylene glycol moiety. No formal studies have been conducted with regards to immunogenicity of the intramuscular route of administration of PLEGRIDY.
6.3 Postmarketing Experience The following adverse reactions have been identified during post-approval use of PLEGRIDY. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Anaphylactic reactions In post marketing experience, serious hypersensitivity reactions, including cases of anaphylaxis, have been reported following PLEGRIDY administration [see Warnings and Precautions ( 5.3 )]. Hepatic injury In post marketing experience, noninfectious hepatitis (including serious hepatitis) cases have been reported following PLEGRIDY administration [see Warnings and Precautions ( 5.1 )] . Pulmonary Arterial Hypertension In postmarketing experience, pulmonary arterial hypertension has been reported following PLEGRIDY administration [see Warnings and Precautions ( 5.8 )] .
Pregnancy, breastfeeding, children and older adults
Pregnancy: Epidemiological data do not suggest a clear relationship between interferon beta use and major congenital malformations, but interferon beta may cause fetal harm based on animal data ( 8.1 ) Severe Renal Impairment: monitor for adverse reactions ( 8.6 )
8.1 Pregnancy Risk Summary Data from a large population-based cohort study, as well as other published studies over several decades, have not identified a drug-associated risk of major birth defects with the use of interferon beta products during early pregnancy. Findings regarding a potential risk for low birth weight or miscarriage with the use of interferon beta products in pregnancy have been inconsistent (see Data ). In a study in pregnant monkeys, administration of interferon beta during pregnancy resulted in an increased rate of abortion ( see Data ). In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown. Data Human Data The majority of observational studies reporting on pregnancies exposed to interferon beta products did not identify an association between the use of interferon beta products during early pregnancy and an increased risk of major birth defects. In a population-based cohort study conducted in Finland and Sweden, data were collected from 1996–2014 in Finland and 2005–2014 in Sweden on 2,831 pregnancy outcomes from women with MS. 797 pregnancies were in women exposed to interferon beta only. No evidence was found of an increased risk of major birth defects among women with MS exposed to interferon beta products compared to women with MS that were unexposed to any non-steroid therapy for MS (n=1,647) within the study. No increased risks were observed for miscarriages and ectopic pregnancies, though there were limitations in obtaining complete data capture for these outcomes, making the interpretation of the findings more difficult. Two small cohort studies that examined pregnancies exposed to interferon beta products (without differentiating between subtypes of interferon beta products) suggested that a decrease in mean birth weight may be associated with interferon beta exposure during pregnancy, but this finding was not confirmed in larger observational studies. Two small studies observed an increased prevalence of miscarriage, although the finding was only statistically significant in one study. Most studies enrolled patients later in pregnancy, which made it difficult to ascertain the true percentage of miscarriages. In one small cohort study, a significantly increased risk of preterm birth following interferon beta exposure during pregnancy was observed. Animal Data PLEGRIDY has not been tested for developmental toxicity in pregnant animals. In monkeys given interferon beta by subcutaneous injection every other day during early pregnancy, no adverse effects on embryofetal development were observed. Abortifacient activity was evident following 3 to 5 doses.
8.2 Lactation Risk Summary Limited published literature has described the presence of interferon beta-1a products in human milk at low levels. There are no data on the effects of interferon beta-1a on milk production. Therefore, the developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for PLEGRIDY and any potential adverse effects on the breastfed infant from PLEGRIDY or from the underlying maternal condition.
8.4 Pediatric Use Safety and effectiveness in pediatric patients have not been established.
8.5 Geriatric Use Clinical studies of PLEGRIDY did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients.
8.6 Renal Impairment Monitor for adverse reactions due to increased drug exposure in patients with severe renal impairment [ see Clinical Pharmacology ( 12.3 ) ].
How it works
The mechanism by which PLEGRIDY exerts its effects in patients with multiple sclerosis is unknown.
Are there biosimilars to Peginterferon Beta-1a?
No. The FDA has not approved a biosimilar yet.
Biologics have biosimilars rather than generics: highly similar versions with no clinically meaningful differences. Only biosimilars the FDA designates as interchangeable can be swapped at the pharmacy without asking the prescriber, where state law allows; the FDA Purple Book lists which ones are.
Brand-name versions
- Plegridy Biogen Idec Inc, approved 2014
Source: Drugs@FDA (via openFDA), checked October 29, 2026. Marketing status is what companies report to the FDA; whether a pharmacy stocks a product, and what your insurance covers, can differ.
Dosage:
we do not reproduce dosing instructions. The right dose depends on the person and the condition and is set by the prescriber or pharmacist. Dosage section of the full label.
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Source: FDA structured product labeling, retrieved through openFDA. Label text is shown as published by the FDA, without editing; long sections are shortened, marked […]. openFDA data are not validated for clinical use — always check the current label and ask a doctor or pharmacist about your own treatment. Set ID 08f0ea03-4e6d-195d-aef4-886e32befa95.