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Peginterferon alfa-2a

Generic name: peginterferon alfa-2a [ peg-in-ter-FEER-on-AL-fa-2 a ]
Brand names: Pegasys, Pegasys ProClick Autoinjector, Pegasys Prefilled Syringe
Dosage form: subcutaneous solution (180 mcg/0.5 mL; 180 mcg/mL)
Drug class: Antiviral interferons

Medically reviewed by on Jul 4, 2022. Written by Cerner Multum.

What is peginterferon alfa-2a?

Peginterferon alfa-2a is used alone or with other medicines to treat chronic hepatitis C in adults and children at least 5 years old.

Peginterferon alfa-2a is also used to treat chronic hepatitis B when the virus begins to damage the liver in adults and children at least 3 years old.

Peginterferon alfa-2a may also be used for purposes not listed in this medication guide.


You should not use peginterferon alfa-2a with ribavirin if you are pregnant, or if you are a man whose sex partner is pregnant. Use effective birth control to prevent pregnancy while taking ribavirin and for at least 6 months after your last dose.

Peginterferon alfa-2a may cause serious or fatal side effects.

Tell your doctor about any new or worsening mood symptoms, such as feeling irritable, hostile, aggressive, depressed, or having thoughts about suicide or hurting yourself.

Call your doctor right away if you have symptoms such as chest pain, fast heartbeats, trouble breathing, numbness or weakness, vision or speech problems, fever, chills, a cough with mucus, burning when you urinate, or bloody diarrhea.

Before taking this medicine

You should not use peginterferon alfa-2a if:

  • you are allergic to any type of interferon alfa; or

  • you have autoimmune hepatitis, or severe liver damage.

When taking peginterferon alfa-2a with other medicine: To make sure all medicines are safe for you, tell your doctor about all your medical conditions, and if you are pregnant or breastfeeding.

Tell your doctor if you have ever had:

Peginterferon alfa-2a may contain an ingredient that can cause serious side effects or death in very young or premature babies. Do not give peginterferon alfa-2a to a child younger than 1 year old.

You may need to have a negative pregnancy test before starting this treatment.

Peginterferon alfa-2a is sometimes used in combination with ribavirin. Both men and women using ribavirin should use effective birth control to prevent pregnancy. Ribavirin can cause birth defects, miscarriage, or death to an unborn baby if the mother or father is using this medicine.

You should not take ribavirin if you are pregnant, or if you are a man and your sex partner is pregnant. Use effective birth control to prevent pregnancy. Keep using birth control for at least 6 months after your last dose of ribavirin.

Tell your doctor right away if a pregnancy occurs while either the mother or the father is using ribavirin.

You should not breastfeed while using peginterferon alfa-2a. Women with HIV or AIDS should not breastfeed a baby. Even if your baby is born without HIV, the virus may be passed to the baby in your breast milk.

How should I use peginterferon alfa-2a?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Peginterferon alfa-2a is injected under the skin, usually once per week on the same day each week. A healthcare provider may teach you how to properly use the medication by yourself.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you don't understand all instructions.

Prepare an injection only when you are ready to give it. Do not use if the medicine looks cloudy, has changed colors, or has particles in it. Call your pharmacist for new medicine.

Peginterferon alfa-2a doses are based on body surface area (height and weight) in children. Your child's dose needs may change if the child is still growing.

Your dose needs may change if you switch to a different brand, strength, or form of this medicine. Avoid medication errors by using only the form and strength your doctor prescribes.

You will need frequent medical tests. Your vision and lung function may also need to be checked.

Each vial (bottle), prefilled syringe, or auto-injector device is for one use only. Throw it away after one use, even if there is still medicine left inside.

Store in the refrigerator, protected from light. Do not shake or freeze this medicine.

Follow the package directions about letting your medicine reach room temperature before injecting your dose. Do not leave the medicine out of a refrigerator for longer than 24 hours.

Use a needle and syringe only once and then place them in a puncture-proof "sharps" container. Follow state or local laws about how to dispose of this container. Keep it out of the reach of children and pets.

What happens if I miss a dose?

Use the medicine as soon as you remember, and then go back to your regular injection schedule. Do not use two doses at one time.

If you are more than 2 days late in using your injection, call your doctor for instructions.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using peginterferon alfa-2a?

Avoid drinking alcohol. It may increase your risk of liver damage.

Avoid driving or hazardous activity until you know how peginterferon alfa-2a will affect you. Your reactions could be impaired.

Using this medicine may not prevent your disease from spreading. Follow your doctor's instructions about how to prevent passing the disease to another person.

Peginterferon alfa-2a side effects

Get emergency medical help if you have signs of an allergic reaction (hives, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Peginterferon alfa-2a can cause life-threatening infections, autoimmune disorders, serious mood or behavior problems, or a stroke.

Call your doctor at once if you have unusual changes in mood or behavior, such as: depression, irritability, aggression, hallucinations, thoughts about hurting yourself, or falling back into a previous pattern of drug addiction.

Peginterferon alfa-2a may cause serious or fatal side effects. Call your doctor at once if you have:

  • severe stomach pain with bloody diarrhea;

  • new or worsening cough, cough with yellow or pink mucus, trouble breathing;

  • numbness, tingling, or burning in your arms or legs;

  • pain or burning when you urinate;

  • sudden numbness or weakness, slurred speech, problems with balance;

  • vision changes;

  • low blood cell counts--fever, chills, tiredness, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin, cold hands and feet, feeling light-headed or short of breath;

  • high or low blood sugar--headache, hunger, confusion, sweating, thirst, increased urination, weakness, fruity breath odor, feeling anxious or shaky, weight loss, or fainting;

  • pancreatitis--severe pain in your upper stomach spreading to your back, nausea and vomiting;

  • thyroid problems--weight changes, skin changes, trouble concentrating, feeling hot or cold all the time; or

  • worsening liver symptoms--swelling around your midsection, nausea, diarrhea, loss of appetite, confusion, drowsiness, yellowing of the skin or eyes, loss of consciousness.

Your next injection may be delayed if you have certain side effects.

Peginterferon alfa-2a can affect growth in children. Tell your doctor if your child is not growing at a normal rate while using this medicine.

Common side effects of peginterferon alfa-2a may include:

  • fever, chills;

  • muscle or joint pain;

  • headache; or

  • feeling weak or tired.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect peginterferon alfa-2a?

Tell your doctor about all your other medicines, especially:

This list is not complete. Other drugs may affect peginterferon alfa-2a, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.