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Avonex (Interferon Beta-1A) - Side Effects and Adverse Reactions



The following serious adverse reactions are discussed in more detail in other sections of labeling:

  • Depression, Suicide, and Psychotic Disorders [see Warnings and Precautions (5.1)]
  • Hepatic Injury [see Warnings and Precautions (5.2)]
  • Anaphylaxis and Other Allergic-Reactions [see Warnings and Precautions (5.3)]
  • Congestive Heart Failure [see Warnings and Precautions (5.4)]
  • Decreased Peripheral Blood Counts [see Warnings and Precautions (5.5)]
  • Seizures [see Warnings and Precautions (5.6)]
  • Autoimmune Disorders [see Warnings and Precautions (5.7)]
  • Laboratory Tests [see Warnings and Precautions (5.8)]

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of AVONEX cannot be directly compared to rates in clinical trials of other drugs and may not reflect the rates observed in practice.

Among 351 patients with relapsing forms of MS treated with AVONEX 30 micrograms (including 319 patients treated for 6 months and 288 patients treated for greater than one year) the most commonly reported adverse reactions (at least 5% more frequent on AVONEX than on placebo) were flu-like symptoms. Symptoms can include chills, fever, myalgia and asthenia occurring within hours to days following an injection. 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. The most frequently reported adverse reactions resulting in clinical intervention (for example, discontinuation of AVONEX or the need for concomitant medication to treat an adverse reaction symptom) were flu-like symptoms and depression.

Table 2 enumerates adverse reactions that occurred with AVONEX-treated patients at an incidence of at least 2% more than that observed in the placebo-treated patients in the pooled placebo-controlled studies in patients with relapsing forms of MS [see Clinical Studies (14)].

Table 2 Adverse Reactions in the Placebo-Controlled Studies
Placebo AVONEX
Adverse Reaction (N = 333) (N = 351)
Body as a Whole
     Headache 55% 58%
     Flu-like symptoms (otherwise      unspecified) 29% 49%
     Pain 21% 23%
     Asthenia 18% 24%
     Fever 9% 20%
     Chills 5% 19%
     Abdominal pain 6% 8%
     Injection site pain 6% 8%
     Infection 4% 7%
     Injection site inflammation 2% 6%
     Chest pain 2% 5%
     Injection site reaction 1% 3%
     Toothache 1% 3%
Nervous System
     Depression 14% 18%
     Dizziness 12% 14%
Respiratory System
     Upper respiratory tract infection 12% 14%
     Sinusitis 12% 14%
     Bronchitis 5% 8%
Digestive System
     Nausea 19% 23%
Musculoskeletal System
     Myalgia 22% 29%
     Arthralgia 6% 9%
     Urinary tract infection 15% 17%
     Urine constituents abnormal 0% 3%
Skin and Appendages
     Alopecia 2% 4%
Special Senses
     Eye disorder 2% 4%
Hemic and Lymphatic System
     Injection site ecchymosis 4% 6%
     Anemia 1% 4%
Cardiovascular System
     Migraine 3% 5%
     Vasodilation 0% 2%


Anaphylaxis and other allergic reactions have occurred in AVONEX-treated patients [see Warnings and Precautions (5.3)]. As with all therapeutic proteins, there is a potential for immunogenicity. In studies assessing immunogenicity in multiple sclerosis patients administered AVONEX for at least 1 year, 5% (21 of 390 patients) showed the presence of neutralizing antibodies at one or more times.

These data reflect the percentage of patients whose test results were considered positive for antibodies to AVONEX using a two-tiered assay (ELISA binding assay followed by an antiviral cytopathic effect assay), and are highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of neutralizing activity in an assay may be influenced by several factors including sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies to AVONEX with the incidence of antibodies to other products may be misleading.

Postmarketing Experience

The following additional adverse reactions have been identified during post-approval use of AVONEX. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

  • Menorrhagia and metrorrhagia
  • Rash (including vesicular rash)
  • Rare cases of injection site abscess or cellulitis requiring surgical intervention


Below is a sample of reports where side effects / adverse reactions may be related to Avonex. The information is not vetted and should not be considered as verified clinical evidence.

Possible Avonex side effects / adverse reactions in 35 year old female

Reported by a consumer/non-health professional from United States on 2011-10-03

Patient: 35 year old female

Reactions: Nausea, Headache, Abortion Spontaneous

Suspect drug(s):

Possible Avonex side effects / adverse reactions in 57 year old male

Reported by a consumer/non-health professional from United States on 2011-10-03

Patient: 57 year old male

Reactions: Musculoskeletal Disorder

Suspect drug(s):
    Start date: 1999-01-07

    Indication: Multiple Sclerosis
    Start date: 2000-04-12
    End date: 2004-01-01

    Start date: 2004-01-01
    End date: 2004-01-01

    Start date: 2004-01-01

Other drugs received by patient: Motrin

Possible Avonex side effects / adverse reactions in 49 year old female

Reported by a consumer/non-health professional from United States on 2011-10-03

Patient: 49 year old female

Reactions: Back Pain, Dysstasia, Gait Disturbance, Ankle Fracture, Fall

Adverse event resulted in: hospitalization

Suspect drug(s):

See index of all Avonex side effect reports >>

Drug label data at the top of this Page last updated: 2012-02-29

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