Peginterferon alfa

Sounds like 'peg-in-ter-FEER-on alfa'

Easy-to-read medicine information about peginterferon alfa – what is it, how to use peginterferon alfa safely and possible side effects.

Type of medicine Also called
  • Immune modulator (modifies the body's immune system)
  • Long-acting interferon
  • Pegasys®
  • Pegasys RBV combination® 
It is important that you do not get pregnant when on this medication. See special instructions below.

What is peginterferon alfa?

  • Peginterferon alfa belongs to a group of medicines called immune modulators.
  • It boosts the body's immune system to fight infection and disease.
  • Peginterferon alfa is a man-made version of a protein called interferon, which is made naturally in our bodies to fight viral infections. 
  • It is used to treat chronic hepatitis B infection and chronic hepatitis C infection (in combination with ribavirin).
  • Peginterferon alfa is available in a pre-filled syringe.


  • The usual dose of peginterferon alfa 180 micrograms ONCE A WEEK, for between 24 and 48 weeks. 
  • Some people may require a different dose, depending on their response to treatment.
  • Always use your peginterferon alfa exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much peginterferon alfa to use, how often to use it, and any special instructions.

How to use peginterferon alfa

  • Peginterferon alfa is given by injection under the skin (called subcutaneous injection).
  • Inject peginterferon alfa into the fatty tissue just under the skin, in the stomach or thigh area. Use a different place each time you give yourself an injection.
  • Inject peginterferon alfa about the same time, on the same day, each week.
  • It is best to inject peginterferon alfa at bedtime, to reduce side effects such as feeling tired.
  • Limit or avoid drinking alcohol while you are taking peginterferon alfa.
  • If you forget to take your dose 1 or 2 days after it was scheduled, you should inject your recommended dose as soon as possible. Take your next injection on the regularly scheduled day.
  • If you forget to take your dose, and it is more than 2 days since you were supposed to take it, call your doctor for instructions. Do not take double the dose.

Special instructions

  • Before starting treatment with peginterferon alfa you will need to complete a range of blood tests to determine whether it is safe for you to proceed with treatment. These tests will also be repeated intermittently during treatment, to monitor your response.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding. It is important that you do not get pregnant when on this medication. Effective birth control is essential while you are taking this medication.

Possible side effects

Like all medicines, peginterferon alfa can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Flu-like symptoms such as fever, chills, muscle aches and sore joints
  • Headache  
  • These are very common when you first start using peginterferon alfa, and lessen after a few weeks
  • Tell your doctor – you may be advised to take paracetamol 
  • Feeling tired
  • Difficulty concentrating
  • Dizziness 
  • Be careful when driving or using tools until you know how this medicine affects you
  • Tell your doctor if troublesome
  • Changes in your mood such as low mood, feeling down, feeling depressed  
  • Feeling anxious
  • Tell your doctor
  • Changes in heartbeat such as fast heart rate or irregular heartbeat
  • Severe chest pain  
  • Tell your doctor immediately or ring HealthLine 0800 611 116
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


Peginterferon alfa interacts with a number of important medications and herbal supplements so check with your doctor or pharmacist.

Learn more

Are you ready for hepatitis C treatment? The Hepatitis Foundation of New Zealand

Credits: Sandra Ponen, Pharmacist.