Peginterferon Alfa 2a

Reviewed on 6/28/2022

What Is Peginterferon Alfa 2a and How Does It Work?

Peginterferon Alfa 2a is a  prescription medication used for the treatment of chronic hepatitis C and other forms of chronic hepatitis.

  • Peginterferon Alfa 2a is available under the following different brand names: Pegasys, Pegasys ProClick

What Are Doses of Peginterferon Alfa 2a?

Adult and pediatric dosage


  • 180 mcg / mL (single-dose)


  • 180 mc Prefilledg/0.5 mL (single-dose)

Chronic Hepatitis C

Adult dosage

  • 180 mcg SC once weekly

Pediatric dosage

  • Aged below 5 years: Safety and efficacy not established
  • Aged above 5 years H4
  • 180 mcg/1.73 m2 SC once weekly with daily ribavirin

Chronic Hepatitis

Adult dosage

  • 180 mcg SC once weekly for 48 weeks

Chronic hepatitis B

Pediatric dosage

  • 180 mcg/1.73 m2 x BSA (maximum dose: 180 mcg) SC once weekly for 48 weeks

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”

What Are Side Effects Associated with Using Peginterferon Alfa 2a?

Common side effects of Peginterferon Alfa 2a include:

  • flu-like symptoms (fever, chills, feeling very hot or very cold, muscle aches, fatigue, headache, muscle or joint pain, nausea, vomiting, stomach pain, cough),
  • dry mouth,
  • loss of appetite,
  • weight loss,
  • trouble sleeping (insomnia),
  • diarrhea,
  • dry skin,
  • temporary hair loss,
  • skin rash,
  • tooth and gum problems, or
  • injection site reactions (redness, swelling, itching, or dryness).

Serious side effects of Peginterferon Alfa 2a include:

  • persistent sore throat or fever,
  • easy or unusual bleeding or bruising,
  • unusually severe fatigue,
  • unusually slow/fast/pounding heartbeat,
  • severe stomach pain with nausea or vomiting,
  • black or tarry stools,
  • vomit that looks like coffee grounds,
  • yellowing eyes or skin,
  • dark urine,
  • increased thirst or urination,
  • bloody diarrhea, or
  • numbness or tingling of arms or legs.

Rare side effects of Peginterferon Alfa 2a include:

  • none 

This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.

What Other Drugs Interact with Peginterferon Alfa 2a?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist about all your products. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions or concerns.

What Are Warnings and Precautions for Peginterferon Alfa 2a?


  • Known hypersensitivity reactions (eg, urticaria, angioedema, bronchoconstriction, anaphylaxis, or Stevens-Johnson syndrome)
  • Autoimmune hepatitis
  • Hepatic decompensation (Child-Pugh score above 6 [class B and C]) in cirrhotic patients with or without HIV coinfection before treatment
  • Use in neonates and infants
  • Combination therapy with ribavirin is contraindicated in females who are pregnant and men whose female partners are pregnant

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Peginterferon Alfa 2a?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Peginterferon Alfa 2a?”


  • Refer to prescribing information of the other HCV antiviral drugs, including ribavirin, for their warnings and precautions
  • May cause birth defects and/or death of the exposed fetus; patients must avoid pregnancy (female patients or female partners of male patients) while taking PEG-INF-Alfa-2a and ribavirin combination therapy
  • Life-threatening or fatal neuropsychiatric reactions may manifest and include suicide, suicidal ideation, homicidal ideation, depression, relapse of drug addiction, and drug overdose; these reactions may occur with and without a history of previous psychiatric illness
  • Hypertension, supraventricular arrhythmias, chest pain, and myocardial infarction were reported; caution with pre-existing cardiovascular disease
  • Suppresses bone marrow function and may result in severe cytopenias; ribavirin may potentiate the neutropenia and lymphopenia induced by alpha interferons; rare occurrences of aplastic anemia observed
  • Development or exacerbation of autoimmune disorders including myositis, hepatitis, thrombotic thrombocytopenic purpura, idiopathic thrombocytopenic purpura, psoriasis, rheumatoid arthritis, interstitial nephritis, thyroiditis, and systemic lupus erythematosus reported
  • May cause or aggravate endocrine disorders including hypothyroidism, hyperthyroidism, hyperglycemia, hypoglycemia, and diabetes mellitus
  • Alpha interferons may induce or exacerbate ophthalmic disorders including decrease or loss of vision, retinopathy including macular edema, retinal artery or vein thrombosis, retinal hemorrhages and cotton wool spots, optic neuritis, papilledema, and serous retinal detachment
  • Patients with CHC with cirrhosis may be at risk of hepatic decompensation and death when treated with alpha interferons
  • Exacerbations of hepatitis during hepatitis B therapy are not uncommon and are characterized by transient and potentially severe increases in serum ALT
  • Dyspnea, pulmonary infiltrates, pneumonia, bronchiolitis obliterans, interstitial pneumonitis, pulmonary hypertension, and sarcoidosis, some resulting in respiratory failure and/or patient deaths, may be induced or aggravated by alpha interferons
  • Serious and severe infections (bacterial, viral, or fungal), some fatal, have been reported during treatment with alpha interferons
  • Ulcerative and hemorrhagic/ischemic colitis, sometimes fatal, have been observed within 12 weeks of starting alpha-interferon treatment
  • Pancreatitis, sometimes fatal, has occurred during alpha interferon and ribavirin treatment
  • Severe acute hypersensitivity reactions (eg, urticaria, angioedema, bronchoconstriction, and anaphylaxis) observed
  • Growth inhibition was observed in children aged 5-17 years with CHC during combination therapy for up to 48 weeks with ribavirin, and also in children aged 3-17 years with CHB for up to 48 weeks during monotherapy
  • Laboratory tests
    • Standard hematological and biochemical laboratory tests recommended for all patients
    • Preform pregnancy screening for females of childbearing potential
    • Administer electrocardiograms if pre-existing cardiac abnormalities exist before combination treatment with ribavirin
    • After initiation, perform hematological tests at 2 and 4 weeks and biochemical tests at 4 weeks
    • Perform additional testing periodically during therapy
  • Drug interaction overview H4
    • Peginterferon Alfa-2a is a weak CYP1A2 inhibitor
    • Theophylline
    • Once-weekly peginterferon Alfa-2a treatment for 4 weeks in healthy subjects was associated with a 25% increase in theophylline AUC
    • If coadministered, monitor theophylline serum levels and consider appropriate dose adjustments
  • NRTIs
    • Hepatic decompensation (including fatalities) was observed when patients coinfected with CHC/HIV received NRTIs
    • Closely monitor for treatment-associated toxicities when peginterferon Alfa-2a/ribavirin combined with other HCV antiviral drugs and NRTIs
    • Refer to prescribing information for other HCV antiviral drugs and the respective NRTIs for guidance regarding toxicity management
    • Consider dose reduction or discontinuation of peginterferon Alfa-2a, ribavirin, or both if worsening toxicities observed
  • Zidovudine
    • Coadministration may increase the risk of developing severe neutropenia and/or anemia
    • Consider discontinuing zidovudine as medically appropriate
    • Consider dose reduction or discontinuation of peginterferon Alfa-2a, ribavirin, or both if worsening clinical toxicities are observed, including hepatic decompensation (eg, Child-Pugh above 6)
  • Methadone
    • Coadministration increases methadone levels by 10-15% from baseline
    • Clinical significance unknown; monitor for potential methadone toxicity

Pregnancy & Lactation

  • There are no adequate and well-controlled studies on pregnant women to inform of drug-associated risk
  • Combination treatment with ribavirin is contraindicated in women who are pregnant and in the male partners of women who are pregnant; significant teratogenic and/or embryocidal effects are demonstrated in all animal species exposed to ribavirin
  • Pregnancy exposure registry
    • Monitors maternal and fetal outcomes of pregnancies of female patients and female partners of male patients exposed to ribavirin during pregnancy or who become pregnant within 6 months following discontinuation of ribavirin
    • Encourage healthcare providers and patients to report such cases by calling 1-800-593-2214
  • Pregnancy testing
    • Treatment with ribavirin or with another HCV drug
    • Females of reproductive potential: Perform before initiation of treatment, monthly during treatment, and for at least 6 months following treatment
    • Males with female partners of reproductive potential: Perform before initiation of treatment, monthly during treatment, and for at least 6 months following treatment
  • Contraception
    • Females of reproductive potential: Use effective contraception during therapy; when receiving combination therapy with ribavirin, use effective contraception during treatment and for at least 6 months after the last dose
  • Infertility
    • Based on its mechanism of action and studies in female monkeys, disruption of the menstrual cycle may occur
    • No female fertility study has been performed
  • Lactation
    • There is no information regarding drug presence in human milk, effects on breastfed infants, or milk production
    • The Centers for Disease Control and Prevention recommends that HIV-infected mothers not breastfeed their infants to avoid potential transmission of HIV; therefore, CHC- and CHB-infected mothers coinfected with HIV should not breastfeed their infants

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