Skip to main content

Peginterferon Alfa-2a (Injection)

Peginterferon Alfa-2a (peg-in-ter-FEER-on AL-fa-2a)

Treats hepatitis B or hepatitis C.

Brand Name(s):

Pegasys, Pegasys Proclick

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. You should not receive it if you had an allergic reaction to peginterferon alfa-2a.

How to Use This Medicine:


  • Your doctor will prescribe your exact dose and tell you how often it should be given. This medicine is given as a shot under your skin.
  • A nurse or other health provider will give you this medicine.
  • You may be taught how to give your medicine at home. Make sure you understand all instructions before giving yourself an injection. Do not use more medicine or use it more often than your doctor tells you to.
  • This medicine should come with a Medication Guide. Ask your pharmacist for a copy if you do not have one.
  • Use this medicine on the same day each week and at about the same time of the day.
  • Double-check that you are giving yourself the correct amount of medicine if you switch between using vials and prefilled syringes or autoinjectors.
  • Do not shake the medicine container.
  • Use the vial, syringe, or autoinjector only 1 time. Throw away any medicine that is leftover.
  • Missed dose:
    • Fewer than 2 days late: Use your medicine as soon as you can, then go back to your regular schedule next week.
    • More than 2 days late: Call your doctor for instructions.
    • Do not use extra medicine to make up for a missed dose.
  • If you store this medicine at home, keep it in the refrigerator. Do not freeze. Do not leave this medicine out of the refrigerator for more than 24 hours. Protect it from light.
  • Throw away used needles in a hard, closed container that the needles cannot poke through. Keep this container away from children and pets.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Some medicines can affect how peginterferon alfa-2a works. Tell your doctor if you are using any of the following:
    • Azathioprine
    • Methadone
    • Telbivudine
    • Theophylline
    • Medicine to treat HIV or AIDS
  • Do not drink alcohol while you are using this medicine.

Warnings While Using This Medicine:

  • This medicine may cause birth defects if either partner is using it together with ribavirin during conception or pregnancy. Tell your doctor right away if you or your partner becomes pregnant. Female patients and female partners of male patients must use 2 forms of birth control during treatment and for 6 months after treatment ends. Female patients must have regular pregnancy tests during combination treatment.
  • Tell your doctor if you are breastfeeding, or if you have kidney disease, other liver disease, diabetes, thyroid problems, an autoimmune disorder (such as psoriasis, lupus, or arthritis), bleeding problems, heart or blood vessel disease, heart rhythm problems, or high blood pressure. Tell your doctor if you have a history of heart attack, stroke, cancer, depression, or drug addiction.
  • This medicine may cause the following problems:
    • New or worsening diabetes, thyroid problems, or autoimmune disorders
    • Vision changes or eye problems
    • New or worsening lung problems
    • High blood pressure, heart rhythm problems, or other heart problems
    • Serious allergic reactions (can be life-threatening)
    • Slowed growth in children
  • This medicine may increase mental or emotional problems. This may lead to thoughts of suicide and violence. Talk with your doctor right away if you have any thoughts or behavior changes that concern you. Tell your doctor if you or anyone in your family has a history of bipolar disorder or suicide attempts.
  • This medicine may make you bleed, bruise, or get infections more easily. Take precautions to prevent illness and injury. Wash your hands often.
  • This medicine can cause diarrhea. Call your doctor if the diarrhea becomes severe, does not stop, or is bloody. Do not take any medicine to stop diarrhea until you have talked to your doctor. Diarrhea can occur 2 months or more after you stop taking this medicine.
  • This medicine may make you dizzy or drowsy. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.
  • You could still give hepatitis B or hepatitis C to other people while you are using this medicine.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Blistering, peeling, or red skin rash
  • Bloody or severe diarrhea
  • Chest pain that may spread to your arms, jaw, back, or neck, trouble breathing, unusual sweating, faintness
  • Fast, slow, pounding, or uneven heartbeat
  • Fever, chills, cough, sore throat, body aches
  • Numbness, tingling, or burning pain in your hands, arms, legs, or feet
  • Sudden and severe stomach pain, nausea, vomiting, lightheadedness
  • Unusual bleeding, bruising, or weakness
  • Unusual thoughts or behaviors, depression, thoughts of hurting yourself or others
  • Vision changes, blurred vision, trouble reading, or eye pain

If you notice these less serious side effects, talk with your doctor:

  • Hair loss
  • Mild diarrhea, nausea, or vomiting
  • Mild flu-like symptoms, such as muscle aches, headache, low fever, or tiredness
  • Redness, pain, itching, or bruising where the shot was given

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088

Last Updated: 3/28/2016
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.

Truven Health Analytics. All rights reserved.

Thomson & A.D.A.M