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Interferon beta-1a

Generic name: interferon beta-1a [ in-ter-FEAR-on-BAY-ta ]
Brand names: Avonex Pen, Avonex Prefilled Syringe, Rebif, Rebif Rebidose, Avonex
Dosage forms: intramuscular kit (30 mcg/0.5 mL), subcutaneous kit (-), subcutaneous solution (22 mcg/0.5 mL; 44 mcg/0.5 mL)
Drug class: Interferons

Medically reviewed by on Aug 4, 2023. Written by Cerner Multum.

What is interferon beta-1a?

Interferon beta-1a is used to treat relapsing forms of multiple sclerosis in adults (including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease).

interferon beta-1a will not cure MS, it will only decrease the frequency of relapse symptoms.

Interferon beta-1a may also be used for purposes not listed in this medication guide.

Interferon beta-1a side effects

Get emergency medical help if you have signs of an allergic reaction (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.

Interferon beta-1a may cause serious side effects. Call your doctor at once if you have:

Common side effects of interferon beta-1a may include:

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.


Interferon beta-1a 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 taking this medicine

You should not use interferon beta-1a if you are allergic to natural or recombinant interferon beta or albumin.

Tell your doctor if you have ever had:

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 interferon beta-1a?

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

Interferon beta-1a 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).

Rebif is injected under the skin, usually 3 times per week (such as Monday, Wednesday, and Friday) at the same time on each dosing day.

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 interferon beta-1a. 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 interferon beta-1a with a diluent, store the mixture in a refrigerator and use it within 6 hours.

The Avonex prefilled syringe or autoinjector 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 interferon beta-1a for a short time at cool room temperature protected from light.

Do not freeze interferon beta-1a, and throw away the medicine if it has become frozen.

Each vial, syringe, or autoinjector 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.

Interferon beta-1a dosing information

Usual Adult Dose for Multiple Sclerosis:

-AVONEX(R): 30 mcg IM once a week:
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

-REBIF(R): 22 mcg or 44 mcg subcutaneously 3 times a week:
Weeks 1 to 2: 4.4 mcg subcutaneously 3 times a week
Weeks 3 to 4: 11 mcg subcutaneously 3 times a week
Weeks 5+: 22 mcg subcutaneously 3 times a week
Weeks 1 to 2: 8.8 mcg subcutaneously 3 times a week
Weeks 3 to 4: 22 mcg subcutaneously 3 times a week
Weeks 5+: 44 mcg subcutaneously 3 times 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 happens if I miss a dose?

For Avonex: 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.

For Rebif: Call your doctor for instructions if you miss a dose.

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 interferon beta-1a?

Avoid injecting interferon beta-1a into skin that is red, bruised, irritated, scarred, or infected.

What other drugs will affect interferon beta-1a?

Other drugs may affect 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.

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.