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Interferon Beta-1a Intramuscular Injection

pronounced as (in ter feer' on)

Why is this medication prescribed?

Interferon beta-1a intramuscular injection is used to treat adults with various forms of multiple sclerosis (MS; a disease in which the nerves do not function properly and people may experience weakness, numbness, loss of muscle coordination, and problems with vision, speech, and bladder control) including:

  • clinically isolated syndrome (CIS; nerve symptom episodes that last at least 24 hours),
  • relapsing-remitting forms (course of disease where symptoms flare up from time to time), or
  • secondary progressive forms (course of disease where relapses occur more often).

Interferon beta-1a is in a class of medications called immunomodulators. It works by decreasing inflammation and preventing nerve damage that may cause symptoms of multiple sclerosis.

How should this medicine be used?

Interferon beta-1a intramuscular injection comes as a solution (liquid) in prefilled injection syringes and in a prefilled automatic injection pen. This medication is injected into a muscle, usually once a week, on the same day each week. Inject interferon beta-1a intramuscular at around the same time of day on your injection days. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Use interferon beta-1a exactly as directed. Do not use more or less of it or use it more often than prescribed by your doctor.

Your doctor may start you on a low dose of interferon beta-1a and gradually increase your dose, not more than once every week.

Interferon beta-1a controls the symptoms of MS but does not cure it. Continue to use interferon beta-1a even if you feel well. Do not stop using interferon beta-1a without talking to your doctor.

Your doctor or nurse will show you or a caregiver how to prepare and inject a dose of interferon beta-1a injection at home. Before you use interferon beta-1a intramuscular for the first time, you or the person who will be giving the injections should also read the manufacturer's information for the patient that comes with it. These instructions describe how to prepare and inject a dose of interferon beta-1a. Be sure that you understand these directions and follow the directions carefully.

Always use a new prefilled syringe and needle or prefilled automatic injection pen for each injection. Never reuse syringes, needles, or automatic injection pens. Discard used syringes, needles, and injection pens in a puncture-resistant container, kept out of reach of children. Talk to your doctor or pharmacist about how to discard the puncture-resistant container.

Always look at the medication in your prefilled syringe or automatic injection pen before you use it. The medication should be clear and colorless. If the solution is cloudy, discolored, or contains particles or if the expiration date marked on the prefilled syringe or automatic injection pen has passed, do not use that prefilled syringe or automatic injection pen.

Talk to your doctor or pharmacist about where on your body you should inject interferon beta-1a intramuscular. If you are using a prefilled syringe, you can inject interferon beta-1a intramuscular in your upper arms or thighs. If you are using a prefilled autoinjection pen, you can inject interferon beta-1a intramuscular in the outer surface of your upper thighs. Use a different spot for each injection. Do not use the same spot two times in a row. Do not inject into an area where the skin is sore, red, bruised, scarred, infected, irritated, or abnormal in any way. Two hours after you inject interferon beta-1 intramuscular, you should check the injection site for a skin reaction such as redness, swelling, or tenderness. Call your doctor if you have a skin reaction at the injection site that does not go away in few days.

Your doctor or pharmacist will give you the manufacturer's patient information sheet (medication guide) when you begin treatment with interferon beta-1a and each time you refill your prescription. Read the information carefully and ask your doctor or pharmacist if you have any questions. You can also visit the Food and Drug Administration (FDA) website ( to obtain the interferon beta-1a Medication Guide.

Other uses for this medicine

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What special precautions should I follow?

Before using interferon beta-1a,

  • tell your doctor and pharmacist if you are allergic to interferon beta-1a, any other interferon medications (Betaseron, Extavia, Plegridy, Rebif), any other medications, natural rubber, latex, or any of the ingredients in interferon beta-1a intramuscular injection. Ask your pharmacist or check the Medication Guide for a list of the ingredients.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • tell your doctor if you drink or have ever drunk large amounts of alcohol and if you have or have ever had an autoimmune disease other than MS (a disease in which the body attacks its own cells; ask your doctor if you are unsure if you have this type of disease); blood problems such as anemia (red blood cells that do not bring enough oxygen to all parts of the body), low white blood cells, easy bruising or bleeding, or blood clots; mental illness such as depression, especially if you have ever thought about killing yourself or tried to do so; other mood disorders or mental illness; seizures; pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness); heart failure or any other heart problem; or liver or thyroid disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while using interferon beta-1a, call your doctor immediately.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are using interferon beta-1a.
  • ask your doctor about the safe use of alcoholic beverages while you are using interferon beta-1a. Alcohol can increase the risk that you will develop serious side effects from interferon beta-1a.
  • you should know that you may have flu-like symptoms such as headache, fever, chills, sweating, muscle aches, nausea, vomiting, and tiredness that may last for a day after your injection. Your doctor may tell you to inject your medication at bedtime and take an over-the-counter pain and fever medication to help with these symptoms. These symptoms usually lessen or go away over time. Talk to your doctor if these symptoms are difficult to manage or become severe.

What special dietary instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

What should I do if I forget a dose?

Inject the missed dose as soon as you remember it. Do not inject interferon beta-1a two days in a row. Do not inject a double dose to make up for a missed dose. Return to your regular dosing schedule the following week. Call your doctor if you miss a dose and have questions about what to do.

What side effects can this medication cause?

Interferon beta-1a may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • headache
  • tight muscles
  • dizziness
  • muscle or joint pain
  • eye problems
  • runny nose or nasal congestion
  • toothache
  • hair loss
  • bruising, pain, redness, swelling, bleeding, or irritation at the injection spot

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

  • new or worsening depression
  • thinking about harming or killing yourself or planning or trying to do so
  • mood changes such as anxiety, nervousness, irritability, or aggression
  • hallucinating (seeing things or hearing voices that do not exist)
  • seizures
  • unexplained weight gain or loss
  • feeling cold or hot all the time
  • trouble breathing when lying flat in bed
  • swelling of the feet, ankles, or lower legs
  • increased need to urinate during the night
  • painful or difficult urination
  • decreased ability to exercise
  • chest pain or tightness
  • fast or irregular heartbeat
  • new or increasing fatigue or shortness of breath
  • pale skin
  • excessive tiredness
  • lack of energy
  • confusion
  • loss of appetite
  • unusual bleeding or bruising
  • pain or swelling in the upper right part of the stomach
  • yellowing of the skin or eyes
  • dark brown urine
  • light-colored bowel movements
  • sore throat, cough, or other signs of infection
  • hives, rash; itching; swelling of the face, throat, tongue, lips, or eyes; difficulty breathing or swallowing; hoarseness; or feeling faint
  • mouth sores
  • blistering or peeling skin
  • blue or black discoloration of skin, swelling, or drainage at the injection site
  • red or bloody stools or diarrhea
  • stomach pain
  • slow or difficult speech
  • purple patches or pinpoint dots (rash) on the skin
  • decreased urination or blood in the urine

Interferon beta-1a may cause other side effects. Call your doctor if you have any unusual problems while using this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online ( or by phone (1-800-332-1088).

What should I know about storage and disposal of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store interferon beta-1a intramuscular prefilled syringes and automatic injection pens in the refrigerator. Do not freeze interferon beta-1a, and do not expose the medication to high temperatures. If a refrigerator is not available, you can store prefilled syringes and injection pens at room temperature, away from heat and light, for up to 7 days.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach.

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website ( for more information if you do not have access to a take-back program.

In case of emergency/overdose

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

What other information should I know?

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body's response to interferon beta-1a.

Do not let anyone else use your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

Brand names

  • Avonex®
Last Revised - 09/15/2023