Avonex (Interferon beta-1a)

How does it work?

Avonex injection contains the active ingredient interferon beta-1a, which is a type of medicine called an immunomodulator.

Interferons are a family of small protein molecules that are produced by cells in response to viral infections or various synthetic and biological inducers. Three major classes of interferons have been identified: alfa, beta and gamma. They work in a complicated way that is not fully understood, but are thought to boost the immune system, causing it to attack infected or abnormal cells.

Interferon beta is used to treat multiple sclerosis (MS). In some people, this disease follows a course of relapse and remission, where symptoms worsen for a while, then improve before worsening again. It is these people who can benefit from interferon beta. The medicine helps to reduce the frequency and severity of the relapses. It is not fully understood how interferon beta works in MS, because the disease and its cause are not fully understood.

Avonex is given by injection into a muscle once a week.

Interferon beta is not effective in all people with multiple sclerosis and, because it can have significant side effects, it is recommended that all patients are assessed by a neurologist before starting treatment.

It is not known how long treatment should be continued for. However, it is recommended that patients should be clinically evaluated after two years of treatment. You may develop neutralising antibodies to this medicine that make it less effective. Treatment should be stopped if your MS becomes progressively worse.

What is it used for?

  • Relapsing/remitting multiple sclerosis (characterised by at least two relapses over the previous three years, without evidence of progression of the disease between relapses) in people who are able to walk unaided
  • Treatment of patients who have experienced a single multiple sclerosis-like attack, severe enough to need treatment with intravenous corticosteroids, if alternative diagnoses have been excluded and they are at high risk of developing clinically definite multiple sclerosis.


  • Treatment with this medicine should only be started by a specialist in multiple sclerosis.
  • Carefully follow the instructions provided with your injections. A different injection site should be used each week.
  • This medicine can cause flu-like symptoms such as aches and pains, fever, chills, sweating, headache, fatigue and nausea. These tend to be worse at the start of treatment and improve with continued treatment. You may want to take a medicine to reduce these symptoms, for example aspirin or ibuprofen, before the injection and for 24 hours after the injection. Ask your doctor or pharmacist for advice.
  • This medicine has been associated with depression that can occur at any time during treatment. You should discuss this with your doctor before starting treatment. It is important to talk to your doctor immediately if you have any distressing thoughts or feelings, thoughts about suicide or self-harm, mood changes, or any other unusual change in behaviour while having treatment with this medicine. It may be necessary to stop treatment.
  • This medicine has rarely been associated with liver problems. Symptoms that could indicate liver problems include unexplained itching, nausea and vomiting, right-sided abdominal pain, loss of appetite or flu-like symptoms; yellowing of the skin or eyes (jaundice); or unusually dark urine. Tell your doctor if you experience any of these symptoms during treatment with this medicine.
  • This medicine may rarely decrease the number of blood cells in your blood. Tell your doctor immediately if you experience any of the following symptoms during your treatment, as they may indicate problems with your blood cells: unexplained bruising or bleeding, purple spots, sore mouth or throat, mouth ulcers, high temperature (fever) or other signs of infection, or suddenly feeling tired, breathless, or generally unwell.
  • During treatment with this medicine you should have regular blood tests to monitor your liver function and the levels of blood cells in your blood.

Use with caution in

  • Seizure disorders, eg due to brain injury or epilepsy
  • History of depression or other mood disorders
  • Heart disease, such as angina, heart failure or irregular heartbeats (arrhythmias)
  • Decreased blood cell production by the bone marrow, causing lower than normal levels of blood cells in the blood
  • Severely decreased kidney function
  • Severely decreased liver function
  • History of liver disease
  • History of alcohol abuse
  • Overactive or underactive thyroid gland.

Not to be used in

  • Children under 12 years of age
  • People with severe depression or thoughts of suicide
  • Uncontrolled epilepsy
  • Pregnancy
  • Breastfeeding.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • This medicine should not be used during pregnancy because it may be harmful to the developing foetus and may increase the risk of miscarriage. Women who could get pregnant should use effective methods of contraception to prevent pregnancy while having treatment with this medicine. If you get pregnant during treatment you should stop using this medicine and consult your doctor immediately. Women wanting to try for a baby should stop using this medicine. Seek medical advice from your doctor.
  • It is not known if this medicine passes into breast milk. The manufacturer states that it should not be used during breastfeeding. Alternatively, breastfeeding can be stopped. This decision will depend on the importance of the medicine to the mother. Seek medical advice from your doctor.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Flu-like symptoms such as aches and pains, fever, chills, sweating, headache, fatigue and nausea. These tend to be worse at the start of treatment and improve with continued treatment.
  • Injection site reactions such as pain, redness or bruising
  • Temporary weakness or rigidity of muscles after the injection that may prevent voluntary movements
  • Flushing
  • Runny nose
  • Loss of appetite
  • Diarrhoea
  • Difficulty in sleeping (insomnia)
  • Depression
  • Rash
  • Pain in the muscles, joints, back or neck
  • Muscle cramps or stiffness
  • Disturbance in the components of the blood
  • Hair loss (alopecia)
  • Heavy or irregular menstrual bleeding
  • Dizziness
  • Under or overactive thyroid
  • Confusion
  • Seizures (convulsions)
  • Inflammation of the liver (hepatitis)

The side effects listed above may not include all of the side effects reported by the drug's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while using this one, to ensure that the combination is safe.

No formal interaction studies have been conducted with this medicine.

There may be an increased risk of side effects on the liver or blood cells if other medicines that can affect the liver or blood cells are used in combination with this one.

This medicine may increase the blood level of the following medicines:

  • antiepileptic medicines
  • certain antidepressants
  • zidovudine.

Other medicines containing the same active ingredient

Rebif also contains interferon beta-1a.

Betaferon contains interferon beta-1b.