Interferon Beta-1a (Intramuscular, Subcutaneous)

Interferon beta-1a is designed for people with relapsing-remitting MS to help prevent and reduce the severity of their flare-ups.


Interferon beta-1a injections are used to reduce the number of flare-ups of symptoms in patients with multiple sclerosis (MS). MS causes inflammation of the nerves which leads to muscle weakness and numbness. It can inhibit muscle coordination and cause problems with speech, vision and bladder control. The medicine is suitable for the relapsing-remitting forms of MS, in which patients experience episodes of symptoms from time to time. Recurring episodes can sometimes lead to permanent disability in which symptoms gradually and continually worsen without further obvious flare-ups. Interferon beta-1a can help to slow the progression of the condition and the development of permanent disability.

Interferons are substances which occur naturally in the body and they help to fight infection and reduce inflammation. Interferon beta-1a is a synthetic version of these substances and is a class of drug known as immunomodulators. It works to minimize inflammation of the nerves in order to prevent and reduce the severity of flare-ups.

In the US, interferon beta-1a is only available with a doctor's prescription. Brand names include Avonex, Avonex Pen, Rebif, Rebif Rebidose, and Rebif Rebidose Titration Pack. Depending on the brand being used, the drug is either injected under the skin or into the muscle.

Conditions Treated?

  • Multiple sclerosis (MS)

Type Of Medicine?

  • Immunomodulator

Side Effects

As well as its needed effects, interferon beta-1a can also cause unwanted side effects, some of which are very serious. Although it is unlikely that patients will experience all side effects, they should familiarize themselves with them in order that they can recognize the appropriate times to seek medical attention.

The following side effects must be reported to a doctor immediately:

  • Fast, irregular, or pounding heartbeat
  • Chest pain or discomfort
  • Shortness of breath
  • Troubled breathing
  • Irregular breathing
  • Chest tightness
  • Throat tightness
  • Cough
  • Sore throat
  • Difficulty swallowing
  • Swollen glands
  • Feeling cold
  • Chills
  • Fever
  • Feeling of warmth
  • Sensitivity to heat
  • Sweating
  • Runny or stuffy nose
  • Sneezing
  • Flu-like symptoms
  • Headache
  • Abdominal or stomach pain or tenderness
  • Black, tarry stools
  • Light-colored stools
  • Diarrhea
  • Constipation
  • Blood in stools or urine
  • Dark urine
  • Loss of bladder control
  • Painful or difficult urination
  • Decreased urine output
  • Heavier menstrual periods
  • Pain or discharge from the vagina
  • Pelvic discomfort, heaviness, or aching
  • Nausea
  • Loss of appetite
  • Weight gain or loss
  • Pain
  • Joint pain
  • Muscle aches
  • Muscle spasms
  • Muscle cramps and stiffness
  • Unsteadiness or clumsiness
  • Dilated neck veins
  • Yellow skin or eyes (jaundice)
  • Pale skin
  • Redness of the face, neck, upper chest, or arms
  • Hives or itching
  • Skin lesions
  • Sores, ulcers, or white spots on the lips or in the mouth
  • Cold sores or blisters on eyes, lips, nose, or genitals
  • Redness, blistering, peeling, or loosening of skin
  • Painful blisters on trunk of body
  • Pinpoint red spots on skin
  • Redness, tenderness, or swelling at the injection site
  • Swelling of the face, eyelids, or lips
  • Swelling of fingers, feet, or lower legs
  • Swelling of the mouth or throat
  • Abnormal bruising or bleeding
  • Bloody nose
  • Bleeding gums
  • Unusual tiredness or weakness
  • Extreme fatigue
  • General feeling of illness or discomfort
  • Mood changes
  • Confusion
  • Nervousness
  • Depressed mood
  • Thoughts of suicide
  • Dizziness
  • Fainting
  • Sudden loss of consciousness
  • Speech problems
  • Reduced hearing
  • Earache
  • Dry skin and hair

The following side effects are less serious and only require medical attention is they become very persistent or severe. They may dissipate as the body adjusts to the medicine. If you have questions about them or are struggling to cope with them, consult your doctor. They may be able to help you find ways to better manage the side effects.

This may not be an exhaustive list of all side effects that may occur while taking interferon beta-1a. If you notice others not listed here, consult your doctor straight away. You could also report new side effects to the FDA, or your doctor may do this on your behalf.

If you are ever unsure as to the seriousness of a side effect, it is always safest to consult your doctor. If your doctor is not available and you feel very unwell, visit the emergency room.


The amount of interferon beta-1a that you take will vary depending on your medical history and the brand of medicine that you are prescribed. Always follow your doctor's dosage instruction over any other recommended dosages. The doses outlined below are averages only. Your doctor may increase your dose as necessary after monitoring your condition and assessing how successfully the medicine is working. Do not increase your dose unless instructed to do so by your doctor.


  • At first, 7.5 mcg injected into the muscle once each week
  • Dose increased by 7.5 mcg each week until maximum dose of 30 mcg weekly


  • At first, between 4.4 and 8.8 mcg injected under the skin 3 times each week
  • Dose increased as needed

How to administer interferon beta-1a injections

The way you use interferon beta-1a will depend on the brand of medicine you use. Always follow the instructions included with the medicine. A doctor or nurse will show you how to administer the injection for the first time. If you are ever unsure as to the correct injection technique, consult your doctor.

You will be given a list of areas of the body in which interferon beta-1a can be injected. You should never inject in the same area twice in a row as doing so could cause irritation or tissue damage. It may be helpful to write down the location of each injection to help you correctly rotate body areas. If the skin is sore, inflamed, bruised, scarred, infected, or abnormal in any other way, do not inject into that area.

Always check the color and consistency of a solution before using it, no matter if you are preparing the solution yourself, using premixed solution, or using an autoinjector pen. If the solution appears to be a different color than usual, or it contains particles, do not use it.

Using Avonex for intramuscular injection:

Avonex is injected into the muscle once each week, and patients should inject it on the same day, and around the same time, each week. Your doctor will gradually increase your dose over a number of weeks.

Avonex is available in powder, solution, and autoinjector pen forms. The powder is provided in individually sealed vials and must be reconstituted with sterile water before use. A new, unopened vial, needle, and syringe must be used for each injection to reduce the risk of infection. The pre-prepared solution is provided in a syringe, and a new syringe and needle must be used for each injection.

When preparing a solution from a powder, add the sterile water directly into the vial and swirl it gently to mix. Do not shake the vial. The mixture should be clear or slightly yellow. Do not use it if there are particles in it. You should use the medicine as soon as possible after mixing, but if necessary you can store the mixture in a syringe in the refrigerator for up to six hours. If you do not use the mixture within 6 hours, dispose of it and prepare a new dose.

Avonex pens are prefilled autoinjectors, which means that they contain the appropriate dose and there is no need to prepare the solution or use separate needles or syringes to administer the injection. The tip of the pen is simply pressed firmly against the skin and the device will automatically inject the solution. A new injector pen should be used for each injection.

Using Rebif for subcutaneous injection:

Rebif is designed to be injected under the skin and should be administered three times each week. Injections should take place around the same time and on the same days each week, and they must be at least 48 hours apart. For example, you could administer the injections on Mondays, Thursdays and Saturdays. It is best to administer the injections in the afternoon or evening, and many patients opt to inject at bedtime so that it becomes easier to remember each dose.

Rebif is either provided in the form of a prefilled syringe or in an autoinjector. There is no need to prepare the medicine yourself. You should always use a new syringe or pen for each injection. If there is any solution still remaining in the syringe or pen, do not inject again, but simply dispose of it.

Disposing of injection equipment

Once you have administered each injection, you must dispose of used needles, syringes, or pens in a puncture-resistant container. These may be provided by your healthcare provider or pharmacy. Ask your doctor or pharmacist how to dispose of the container once full.

Missed doses

If you miss a dose of interferon beta-1a, administer it as soon as you remember. If your next dose is scheduled for the following day, skip that dose. You should never inject this medicine two days in a row. Never take double doses of interferon beta-1a to make up for a missed dose as doing so could result in serious side effects.


Interferon beta-1a can interact with other medicines and cause a variety of unwanted effects. In some instances, interactions can increase the risk of side effects or cause secondary health complications, or they may simply result in some of your medicines being less effective than usual.

Make sure to tell your doctor about all the medicines you currently take. This includes those prescribed to you, those purchased over the counter, and any herbal supplements or multivitamins you consume. It may be helpful to keep a list of the medicines you take which you can present to each doctor, nurse, or pharmacist you have appointments with. Once you have been prescribed interferon beta-1a, be sure to let all your other doctors know.

It is particularly important to tell your doctor if you take zidovudine (brand name Retrovir). This is an antiretroviral medicine used to prevent and treat HIV and AIDS. It can increase the risk of certain side effects associated with interferon beta-1a. If possible, your doctor may avoid prescribing interferon beta-1a, or they may change zidovudine to an alternative medication. If both drugs are necessary, your doctor may adjust your dosages or give you new instructions as to how to take your medicines.


Interactions with other medical problems

The following medical conditions may be worsened by interferon beta-1a. Depending on the severity of your condition, your doctor may decide not to prescribe interferon beta-1a, or they may administer lower doses or monitor you more closely than usual.

Reduced immunity

Interferon beta-1a can reduce the body's ability to fight off infection. It's important to report signs of an infection to your doctor quickly in order that they can monitor your condition and administer appropriate treatment to help clear the infection. Symptoms of infection include:

  • Fever, chills, and other flu-like symptoms
  • Sore throat
  • Hot, warm, red, swollen, or inflamed areas of skin
  • Pus or discharge


You should not use interferon beta-1a if you have had an allergic reaction to the medicine in the past, or to other interferon medicines (such as Betaseron, Plegridy, or Extavia), or to human albumin. It is safest to tell your doctor about all allergies you suffer from or have had in the past so that they can check that you are not allergic to any of the ingredients in interferon beta-1a. Be sure to mention drug, chemical, dye, food, pollen, and animal allergies.

Pregnancy and breastfeeding

There have not been adequate reproductive studies into interferon beta-1a to understand what effects the drug may have during pregnancy or if it may be harmful to the fetus. For this reason, use of the drug during pregnancy is not recommended unless the potential benefits of the drug far outweigh potential risks to the fetus. If you become pregnant or want to become pregnant while taking interferon beta-1a, consult your doctor. Do not suddenly stop taking the drug if you learn that you are pregnant, but speak to your doctor as soon as possible.

It is not known whether interferon beta-1a is excreted in breast milk, and if so, what effects it could have on nursing infants. If you are breastfeeding, talk to your doctor about the potential risks of the drug. You may have to decide whether it is safer to avoid taking interferon beta-1a in order to breastfeed or to stop breastfeeding in order to take the drug.

Pediatric use

The safety and efficacy of interferon beta-1a have not been established in the pediatric population. The drug is therefore not recommended for children.

Geriatric use

Although there have been few studies performed to assess the performance of interferon beta-1a in elderly patients, there is no evidence to suggest that it is any less useful to the geriatric population than it is for younger adults. However, elderly patients are more likely to have age-related, kidney, liver, or heart problems, which may result in them being more sensitive to the drug's effects and more susceptible to side effects or to worsening health conditions. Doctors may therefore be more cautious when prescribing to this population. They may administer lower doses initially, or they may want to monitor the patient more closely than usual to check for adverse effects.


Vials, autoinjector pens, and prefilled syringes of interferon beta-1a should be stored in the refrigerator where possible. They should be removed from the fridge 30 minutes before use in order that they can reach room temperature. Never attempt to heat up the medicine quicker in the microwave or in hot water.

If refrigeration is not possible, interferon beta-1a may be stored at room temperature but its lifespan will be reduced as follows:

  • Rebif prefilled syringes '30 days
  • Avonex powder vials '30 days
  • Avonex autoinjector pens ' 7 days
  • Avonex prefilled syringes ' 7 days

If storing the medicine at room temperature, keep it away from direct light and do not allow it to heat above 77 degrees Fahrenheit.

Check the appearance of interferon beta-1a before each use. If it appears to contain particles or has changed color, do not use it. If using the powder form of the medicine, you must first add sterile water and then check the mixture for signs of discoloration or changes in consistency.

Always keep interferon beta-1a and all injecting equipment out of reach and sight of children and pets.

Used needles should be stored in a hard, closed container which cannot be punctured. This should be stored out of reach and sight of children and pets, and, once full, disposed of according to the instructions of your healthcare provider.

If you have leftover or expired interferon beta-1a, ask your healthcare provider how to dispose of it. The medicine should not be flushed down the toilet or thrown in the trash, as it could come to harm other people or the environment. Your healthcare provider, pharmacy, or local garbage or recycling department may have a medicine take-back program available which will ensure the drug is safely disposed of.


Interferon beta-1a is an immunomodulator which works to reduce the severity of flare-ups in people with multiple sclerosis (MS). It may also help to prevent flare-ups. By minimizing the frequency and severity of episodes, it can help to slow the progression of the disease and the progression of permanent disability. It is suitable for patients with the relapsing-remitting forms of MS.

Mild side effects associated with interferon beta-1a include sleeping problems, heartburn, indigestion and sour stomach, and hair loss. These do not require medical attention unless they become very severe or persistent, and they may dissipate when the body adjusts to the drug. If patients experience breathing problems, chest pain, signs of infection, abdominal pain, unusual bowel movements, problems with urination, pelvic pain, pain, aches, spasms or stiffness in muscles or joints, jaundice, rash or other skin problems, abnormal bleeding, mood changes or depression, or hearing problems, they should consult their doctor straight away.

Interferon beta-1a is designed to be injected either into the muscle (intramuscularly) or under the skin (subcutaneously). The way in which it is administered depends on the brand of interferon beta-1a which is prescribed. Avonex is injected into the muscle, typically once each week. Rebif is injected under the skin, usually three times each week. The medicine may be provided premixed in prefilled syringes or in autoinjector pens, or in powder form in vials which must be reconstituted with sterile water in order to be injected.

Patients should tell their doctor about all the medicine they currently take in case of harmful interactions. It is particularly important to mention zidovudine (Retrovir) which may increase the risk of certain side effects when taken at the same time as interferon beta-1a.

Interferon beta-1a is not suitable for patients who have had an allergic reaction to it in the past, or an allergic reaction to other interferon medicines or to human albumin. It should be used with caution in patients with mental health problems, history of alcohol abuse, heart problems, bone marrow problems, autoimmune disorders, thyroid problems, liver disease, and seizures or epilepsy. It can make the body less capable of fighting off infection, so patients should report signs of infection to their doctor as soon as possible.

There is little evidence as to the safety and efficacy of interferon beta-1a in children, so it is not recommended for the pediatric population. It appears to be effective in elderly patients, but they may have age-related conditions which could make them more sensitive to its harmful effects. The drug should not be taken by pregnant women unless the benefits of the medicine far outweigh potential risks to the fetus, and it is not recommended for use while breastfeeding.