Why AVONEX® (interferon beta-1a)?


AVONEX works on 3 key areas for the treatment of relapsing MS

In 2 clinical trials of more than 600 people (301 in Study 1, 383 in Study 2) with relapsing MS, AVONEX was tested against a placebo, or "fake" treatment—a standard way to measure if a drug works as expected. Patients received 30 micrograms of AVONEX or placebo by intramuscular (IM) injection once weekly.

  • In the first study, which took place over 2 years, 158 people with relapsing MS taking AVONEX were compared with 143 people with relapsing MS taking placebo. Not all participants continued in the study to the end of year 2
  • In the second study, 193 people with relapsing MS who had recently experienced a first flare-up were given AVONEX and compared with 190 people with relapsing MS who were given placebo. Participants were followed for up to 3 years

In these clinical trials, AVONEX was found to:

Slow disability progression

At the end of the 2-year clinical trial (Study 1), 78% (67/85) of people taking AVONEX had no increase in disability, compared with 65% (58/87) of people taking placebo.

  • The percentage of people with increased disability at 2 years was 22% in the AVONEX group and 35% in the placebo group

People taking AVONEX were 37% less likely to have increased disability at 2 years. 

Reduce relapses

In people who took AVONEX for the full 2-year study (Study 1), AVONEX reduced relapses by 32% compared with placebo. 

  • The annual relapse rate was 0.61 per person-year in the AVONEX-treated group and 0.90 per person-year in the placebo-treated group

When including the people enrolled in the study who didn’t take AVONEX for the full 2 years, AVONEX reduced relapses by 18% compared with placebo.

  • The annual relapse rate was 0.67 per person-year in the AVONEX-treated group and 0.82 per person-year in the placebo-treated group

Reduce risk of relapse at 3 years

In the 3-year clinical study (Study 2) of people who had only experienced one flare-up,* people taking AVONEX were 44% less likely to have a second relapse at 3 years compared with people taking placebo. 

Reduce brain lesions on MRI

In the 2-year study (Study 1), AVONEX reduced the number of gadolinium-enhancing (Gd+) lesions by 75% compared with the beginning of the study.

  • At the start of the study, people in the AVONEX group had 3.2 Gd+ lesions vs 0.8 lesions after 2 years on AVONEX

In the 3-year study (Study 2), AVONEX reduced the size of T2 lesions by 91% compared with placebo at 18 months. 

  • Change in T2 lesion volume from the start of the study was 28 mm3 in the AVONEX group versus 313 mm3 in the placebo group

*A study of people who had experienced a first flare-up and had lesions consistent with MS on MRI. In this study a relapse was defined as 1) a new clinical sign of MS that differed from the patient’s presentation when they entered the study or 2) an increase of at least 1.5 Expanded Disability Status Scale (EDSS) points or 3) further worsening noted at 2 months or the patient withdrew before completing 2 months of treatment.

The placebo group experienced a 30% reduction from baseline in the number of Gd+ lesions after 2 years.


Experience and safety in relapsing MS

Understanding safety and potential side effects

Are you and your healthcare provider considering AVONEX? If so, there are a few important topics to discuss. To help prepare for your discussion, you can learn more below. 

The safety of AVONEX was studied in 2 well-controlled clinical trials conducted over 2 to 3 years. 

Understanding serious side effects

Do not take AVONEX if you are allergic to interferon beta or any of the ingredients in AVONEX.

Before beginning treatment, you should discuss with your healthcare provider the potential benefits and risks associated with AVONEX.

AVONEX can cause serious side effects. Tell your healthcare provider right away if you have any of the symptoms listed below while taking AVONEX.

Depression, suicidal thoughts, hallucinations, or other behavioral health problems

Some people taking AVONEX may develop mood or behavior problems including irritability (getting upset easily), depression (feeling hopeless or feeling bad about yourself), nervousness, anxiety, aggressive behavior, thoughts of hurting yourself or suicide, or hearing or seeing things that others do not hear or see (hallucinations).

Liver problems, or worsening of liver problems including liver failure and death. Tell your healthcare provider right away if you have any of these symptoms:

  • nausea
  • loss of appetite
  • tiredness
  • dark colored urine and pale stools
  • yellowing of your skin or the white part of your eye
  • bleeding more easily than normal
  • confusion
  • sleepiness

During your treatment with AVONEX you will need to see your healthcare provider regularly and have regular blood tests to check for side effects. Tell your healthcare provider about all the medicines you take and if you drink alcohol before you start taking AVONEX.

Serious allergic reactions and skin reactions. Symptoms of serious allergic and skin reactions may include:

  • itching
  • swelling of the face, eyes, lips, tongue, or throat
  • trouble breathing
  • anxiousness
  • feeling faint
  • skin rash, hives, sores in your mouth, or your skin blisters and peels

Get emergency help right away if you have any of these symptoms. Talk to your healthcare provider before taking another dose of AVONEX.

Heart problems, including heart failure

Some people who did not have a history of heart problems developed heart muscle problems or congestive heart failure after taking AVONEX. If you already have heart failure, AVONEX may cause your heart failure to get worse. Call your healthcare provider right away if you have worsening symptoms of heart failure such as shortness of breath or swelling of your lower legs or feet while using AVONEX.

  • Some people using AVONEX may have other heart problems including low blood pressure, fast or abnormal heartbeat, chest pain, and heart attack or heart muscle problem (cardiomyopathy)

Blood problems

AVONEX can affect your bone marrow and cause low red and white blood cell and platelet counts. In some people, these blood cell counts may fall to dangerously low levels.


Some people have had seizures while taking AVONEX, including people who have never had seizures before. Tell your healthcare provider right away if you have a seizure.

Thrombotic microangiopathy (TMA)

TMA is a condition that involves injury to the smallest blood vessels in your body. TMA can also cause injury to your red blood cells (the cells that carry oxygen to your organs and tissues) and your platelets (cells that help your blood clot) and can sometimes lead to death.

Autoimmune diseases

Problems with easy bleeding or bruising (idiopathic thrombocytopenia), thyroid gland problems (hyperthyroidism and hypothyroidism), and autoimmune hepatitis have happened in some people who use AVONEX.

Understanding most common side effects

It’s important to talk with your healthcare provider about the most common side effects of AVONEX and how to help manage them. The most common side effects of AVONEX include:

Flu-like symptoms

Most people who take AVONEX have flu-like symptoms early during the course of therapy. Usually, these symptoms last for a day after the injection. For many people, these symptoms lessen or go away over time. Symptoms may include:

  • muscle aches
  • fever
  • tiredness
  • chills

These are not all of the possible side effects of AVONEX. Call your healthcare provider for medical advice about side effects.

Additional considerations


Additional information for patients considering pregnancy and breastfeeding

Should I take AVONEX if I’m pregnant?

Before you use AVONEX, tell your healthcare provider if you are pregnant or plan to become pregnant. It is not known if AVONEX will harm your unborn baby.

Can I take AVONEX while I’m breastfeeding?

Before you use AVONEX, tell your healthcare provider if you are breastfeeding or plan to breastfeed. AVONEX may pass into your breastmilk. Talk to your healthcare provider about the best way to feed your baby if you use AVONEX.