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Generic name: interferon beta-1ain-ter-FEAR-on-BAY-ta ]
Drug class: Interferons

Medically reviewed by Philip Thornton, DipPharm. Last updated on Aug 22, 2022.

What is Avonex?

Avonex is made from human proteins. Interferons help the body fight viral infections.

Avonex is used to treat relapsing multiple sclerosis (MS) in adults (including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease).

Avonex will not cure MS, it will only decrease the frequency of relapse symptoms.


Avonex can harm your liver. Call your doctor if you have symptoms such as nausea, loss of appetite, tiredness, confusion, easy bruising or bleeding, dark urine, clay-colored stools, or yellowing of your skin or eyes.

Some people have thoughts about suicide while using interferon beta-1a. Stay alert to changes in your mood or symptoms. Report any new or worsening symptoms to your doctor.

Before using Avonex, tell your doctor if you are allergic to any drugs, or if you have liver disease, a thyroid disorder, epilepsy or other seizure disorder, heart disease, chest pain (angina), congestive heart failure, a heart rhythm disorder, or a history of depression or suicidal behavior.

Before taking this medicine

You should not use Avonex if you are allergic to natural or recombinant interferon beta or albumin.

To make sure Avonex is safe for you, tell your doctor if you have:

  • depression, mental illness, or suicidal thoughts or actions;

  • liver disease;

  • bleeding problems or a blood clot;

  • low blood cell counts;

  • heart disease;

  • a thyroid disorder;

  • a latex allergy;

  • an autoimmune disorder such as rheumatoid arthritis, lupus, or psoriasis;

  • a seizure; or

  • if you drink alcohol.

Some brands of interferon beta-1a contain donated human plasma and may contain viruses or other infectious agents. Donated plasma is tested and treated to reduce the risk of contamination, but there is still a small possibility it could transmit disease. Ask your doctor about any possible risk.

Tell your doctor if you are pregnant or plan to become pregnant, or if you are breastfeeding.

Interferon beta-1a is not approved for use by anyone younger than 18 years old.

How should I use Avonex?

Use Avonex exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Avonex is given by injection. 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.

Avonex is injected into a muscle, usually once weekly at bedtime, on the same day each week (such as every Monday).

The powder form of this medicine must be mixed with a liquid (diluent) before using it. Prepare an injection only when you are ready to give it. Do not use if the medicine has changed colors or has particles in it. Call your pharmacist for new medicine.

Your care provider will show you where on your body to inject Avonex. Use a different place each time you give an injection. Do not inject into the same place two times in a row.

About 2 hours after your injection, check for skin redness, swelling, or pain where you gave the injection. Call your doctor if you have a skin reaction that does not go away within a few days.

This medicine can cause flu-like symptoms, especially when you first start using it. You may be given other medications to help prevent these symptoms. Keep using these medicines for as long as your doctor has prescribed.

You will need frequent medical tests.

Each prefilled syringe or injection pen is for one use only. Throw it away after one use, even if there is still medicine left inside.

Store this medicine in the refrigerator. Protect from light and do not freeze.

After mixing the powder form of Avonex (single-use vial) with a diluent, store the mixture in a refrigerator and use it within 6 hours.

The Avonex prefilled syringe may be removed from the refrigerator about 30 minutes before your injection, to reach room temperature. Do not warm the medicine under hot water.

You may also store Avonex for a short time at cool room temperature protected from light.

  • Do not leave the prefilled syringe out of a refrigerator for longer than 7 days.

  • Do not leave the Avonex vial out of a refrigerator for longer than a total of 30 days.

Do not freeze. Throw away the medicine if it has become frozen.

Each vial or syringe is for one use only. Throw it away after one use, even if there is still medicine left inside.

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 can, but do not inject Avonex two days in a row. Do not use two doses at one time.

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 Avonex?

Avoid injecting Avonex into skin that is red, bruised, irritated, scarred, or infected.

Avonex side effects

Get emergency medical help if you have signs of an allergic reaction to Avonex (hives, itching, anxiety, 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).

Interferon beta-1a can cause life-threatening blood clots in the small blood vessels inside your organs, such as your brain or kidneys. Seek medical help right away if you have symptoms of this condition, such as a fever, tiredness, decreased urination, bruising, or nosebleeds.

Call your doctor at once if you have:

  • pain, swelling, bruising, redness, oozing, or skin changes where the injection was given;

  • a light-headed feeling, like you might pass out;

  • unusual changes in mood or behavior (feeling hopeless, anxious, nervous, irritable, or depressed);

  • thoughts about suicide or hurting yourself;

  • easy bruising, unusual bleeding;

  • a seizure;

  • heart problems - swelling, rapid weight gain, feeling short of breath, rapid heartbeats, chest pain spreading to your jaw or shoulder, nausea, sweating;

  • liver problems - nausea, loss of appetite, tiredness, confusion, easy bruising or bleeding, dark urine, clay-colored stools, or jaundice (yellowing of your skin or eyes);

  • signs of infection - fever, chills, cough with mucus, bloody diarrhea, pain or burning when you urinate; or

  • thyroid problems - mood swings, trouble sleeping, tiredness, hunger, diarrhea, pounding heartbeats, muscle weakness, sweating, dry skin, thinning hair, menstrual changes, weight changes, puffiness in your face, feeling more sensitive to hot or cold temperatures.

Common Avonex side effects may include:

  • low blood cell counts;

  • skin changes where the injection was given;

  • depression;

  • abnormal liver function tests;

  • stomach pain; or

  • flu symptoms - headache, fever, chills, chest pain, back pain, tiredness, weakness, muscle aches.

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.

Dosing information

Usual Adult Dose for Multiple Sclerosis:

30 mcg IM once a week:
titration dose to reduce the incidence and severity of influenza-like symptoms:
Week 1: 7.5 mcg IM once a week
Week 2: 15 mcg IM once a week
Week 3: 22.5 mcg IM once a week
Week 4+: 30 mcg IM once a week

Use: For the treatment of patients with relapsing forms of multiple sclerosis to slow the accumulation of physical disability and decrease the frequency of clinical exacerbations. Patients with multiple sclerosis in whom efficacy has been demonstrated include patients who have experienced a first clinical episode and have MRI features consistent with multiple sclerosis

What other drugs will affect Avonex?

Other drugs may interact with interferon beta-1a, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Where can I get more information?

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

Frequently asked questions

More about Avonex (interferon beta-1a)

Patient resources

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Professional resources

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Further information

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