Pronunciation: a-vuh-necks
Generic name: interferon beta-1a
Dosage form: single-dose prefilled syringe/autoinjector for intramuscular use (30 mcg/0.5 mL)
Drug class: Interferons

Medically reviewed by Carmen Pope, BPharm. Last updated on Aug 20, 2025.

What is Avonex?

Avonex is used to treat relapsing multiple sclerosis (MS) in adults (including clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease). Avonex is given by injection into a muscle, usually once weekly at bedtime.

Avonex’s mechanism of action resembles that of interferons which are proteins naturally produced by our immune system that help regulate the body’s immune response and fight viral infections. Avonex contains interferon beta 1-a, which is a man-made form of interferon that works in the same way, binding to specific receptors on cell surfaces and decreasing the activity of immune cells that attack the myelin sheath, reducing inflammation in the central nervous system, and helping to suppress the autoimmune response that characterizes MS. Avonex belongs to the drug class called interferons. It may also be called an immunomodulator.

Avonex (interferon beta-1a) gained FDA approval on May 17, 1996. There is no Avonex generic (more correctly called a biosimilar).

• Another form of interferon beta-1a, called Rebif, also used for MS, is given 3 times a week by subcutaneous (under the skin) injection.

Warnings

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

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.

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.

Storage Instructions:

• Store in refrigerator, protect from light, do not freeze
• Prefilled syringe/autoinjector: Remove 30 minutes before injection to reach room temperature
• Do not leave the prefilled syringe/autoinjector out of the refrigerator for longer than 7 days.

Avonex side effects

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

• breathing difficulties. Pulmonary arterial hypertension can occur with interferon beta products,
  including Avonex. Symptoms may include new or increasing fatigue or shortness of breath.

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 the FDA at 1-800-FDA-1088.

Related/similar drugs

Dosing Information

Usual Adult Maintenance Dose of Avonex for Multiple Sclerosis:

• 30 mcg IM once a week.

Titrate the dose as follows to reduce the incidence and severity of influenza-like symptoms:

• Week 1: 7.5 mcg IM once weekly
• Week 2: 15 mcg IM once weekly
• Week 3: 22.5 mcg IM once weekly
• Week 4+: 30 mcg IM once weekly.

Available forms: Avonex single-dose prefilled syringe and single-dose prefilled autoinjector.

Missed 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.

Overdose

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

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.

Avonex ingredients

Active ingredient: interferon beta-1a
Inactive ingredients: Avonex Single-Dose Prefilled Syringe: arginine hydrochloride, glacial acetic acid, polysorbate 20, sodium acetate trihydrate in water for injection.

Inactive ingredients: Avonex Single-Dose Prefilled Autoinjector Pen: arginine hydrochloride, glacial acetic acid, polysorbate 20, sodium acetate trihydrate in water for injection. 

Who makes Avonex?

Biogen Inc. makes Avonex.

Frequently Asked Questions

How long does it take for Avonex to work?

Avonex typically takes 3-6 months to show its full effect in reducing MS relapses. Some patients may notice improvements in fatigue and overall well-being within the first few weeks, but the medication's primary benefit of reducing relapse frequency and slowing disability progression becomes more apparent over time. It's important to continue treatment even if you don't immediately notice changes, as the medication works to prevent future MS activity.

Can I travel with Avonex injections?

Yes, you can travel with Avonex, but it requires careful planning. Keep medication in its original packaging with prescription labels. For air travel, pack Avonex in carry-on luggage with a cooling pack (but not frozen). Bring a doctor's letter explaining your medical need for the injection.

For international travel, research medication regulations in your destination country. Consider bringing extra supplies in case of delays. Avonex can be stored at room temperature for up to 7 days (prefilled syringe) or 30 days (vial) if refrigeration isn't available.

What's the difference between Avonex and Rebif?

Both Avonex and Rebif contain interferon beta-1a, but they differ in dosing and administration. Avonex is given once weekly by intramuscular injection (into the muscle), while Rebif is given three times weekly by subcutaneous injection (under the skin). Rebif typically has a higher cumulative weekly dose.

Both medications have similar effectiveness for MS treatment, but some patients may prefer the less frequent Avonex injections, while others may tolerate the smaller, more frequent Rebif doses better. Your neurologist can help determine which is best for your situation.

How can I manage flu-like symptoms from Avonex?

Flu-like symptoms are common, especially when starting Avonex, but usually improve over time. To minimize symptoms: take Avonex at bedtime so you sleep through the worst effects, pre-treat with over-the-counter pain relievers like acetaminophen or ibuprofen 30 minutes before injection and continue for 24 hours after, stay well-hydrated, use a heating pad for muscle aches, and ensure adequate rest.

The dose titration schedule (starting with lower doses) also helps reduce these symptoms. Most patients find flu-like effects diminish significantly after 2-3 months of treatment.

Can I drink alcohol while taking Avonex?

While there's no absolute prohibition on alcohol with Avonex, you should use caution. Both Avonex and alcohol can affect liver function, so combining them may increase the risk of liver problems. Additionally, alcohol can worsen some MS symptoms like fatigue, balance problems, and depression. If you choose to drink, do so in moderation and discuss your alcohol consumption with your healthcare provider, especially if you have any liver function abnormalities or are taking other medications.

Where should I rotate injection sites for Avonex?

Avonex is given by intramuscular injection, typically in the thigh (vastus lateralis muscle) or upper arm (deltoid muscle). Rotate between different sites to prevent tissue damage and injection site reactions. For thigh injections, alternate between left and right thighs, and vary the exact location within each thigh. If using the upper arm, you may need assistance from someone else for proper injection technique. Keep a record of injection sites to ensure proper rotation. Never inject into areas that are red, bruised, infected, or have scar tissue.

What blood tests do I need while taking Avonex?

Regular monitoring is essential while taking Avonex. Typical tests include: complete blood count (CBC) to check for low white blood cells, red blood cells, or platelets; liver function tests to monitor for hepatotoxicity; and thyroid function tests since Avonex can affect thyroid function. Initially, these tests may be done monthly for the first few months, then every 3-6 months once you're stable. Your neurologist will determine the appropriate testing schedule based on your individual situation and any side effects you experience.

Can I get pregnant while taking Avonex?

If you're planning to become pregnant or become pregnant while taking Avonex, discuss this immediately with your healthcare provider. Avonex is pregnancy category C, meaning effects on pregnancy aren't fully known. Some studies suggest interferons may increase risk of miscarriage.

Your neurologist will weigh the benefits of continued MS treatment against potential risks to pregnancy. There are alternative MS treatments that may be safer during pregnancy. Don't stop Avonex abruptly without medical supervision, as this could lead to MS relapses.

Is there financial assistance available for Avonex?

Yes, several options exist to help with Avonex costs. Biogen, the manufacturer, offers the Avonex Patient Support Program which may provide co-pay assistance for eligible patients with commercial insurance. The program may cover up to a certain amount per prescription.

Additionally, patient assistance programs are available for uninsured or underinsured patients who meet income requirements. The National MS Society also provides information about financial assistance programs. Contact Biogen's patient support services or speak with your healthcare provider's financial counselor to explore available options.

What should I do if I experience injection site reactions?

Mild injection site reactions (redness, swelling, pain) are common and usually resolve within a few days. Apply ice before injection and heat afterward to minimize discomfort. However, watch for signs of serious reactions: persistent pain, increasing redness or swelling after 2-3 days, skin breakdown or ulceration, blue-black discoloration, or drainage from the injection site. These could indicate injection site necrosis, which requires immediate medical attention.

Always rotate injection sites and never inject into irritated or damaged skin. If reactions persist or worsen, contact your healthcare provider.

Can I receive vaccines while taking Avonex?

Generally, inactivated (killed) vaccines are safe while taking Avonex, but live vaccines should typically be avoided as they may pose risks for people on immunomodulatory therapy. Common safe vaccines include the flu shot (inactivated), the pneumonia vaccine, and the hepatitis B vaccine.

However, timing and specific recommendations can vary. Always inform healthcare providers that you're taking Avonex before receiving any vaccine. Your neurologist and primary care provider should coordinate your vaccination schedule to ensure optimal protection while maintaining MS treatment safety.

Avonex Biosimilars

Biosimilar and interchangeable products are biological products that are highly similar to and have no clinically meaningful differences from the reference product.

Reference products

These are biological products that have already been approved by the FDA, against which biosimilar products are compared. There are 2 for Avonex.

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Further information

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

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