Key takeaways

  • Avonex is a prescription drug that treats relapsing forms of multiple sclerosis (MS) in adults, such as relapsing-remitting MS, active secondary progressive MS, and clinically isolated syndrome.
  • Common mild side effects of Avonex are flu-like symptoms, dizziness, nausea, hair loss, and headache. Serious side effects may include depression, liver damage, and heart failure.
  • Avonex is administered via injection into a muscle once weekly, and the recommended dosage typically increases over a 4-week period to reach a maintenance dosage of 30 micrograms (mcg).

Avonex is a prescription drug that’s used to treat relapsing forms of multiple sclerosis (MS) in adults. For details on what Avonex is used for, see the “Avonex uses” section.

Avonex basics

Avonex is a liquid solution that you inject into a muscle once weekly.

Avonex contains the drug interferon beta-1a, which is a biologic medication. A biologic is made from parts of living organisms.

Avonex isn’t available in a biosimilar form. (Biosimilars are like generic drugs. But unlike generics, which are made for non-biologic drugs, biosimilars are made for biologic drugs.) Instead, interferon beta-1a comes only as the brand-name drug Avonex.

Read on to learn more about Avonex’s uses, side effects, dosage, and more.

Avonex is used to treat certain forms of multiple sclerosis (MS).

Specifically, Avonex is used to treat relapsing forms of MS. (A relapse is a time of new or worsening symptoms.) Avonex is used to treat the following in adults:

  • Relapsing-remitting MS. With this form of MS, you have times when your MS symptoms worsen then get better. “Remitting” means getting better.
  • Active secondary progressive MS. With this form of MS, symptoms continue to worsen without getting better.
  • Clinically isolated syndrome (CIS). This is an episode of symptoms similar to those of MS, and it lasts for 24 hours or more. CIS isn’t a true form of MS, and it may or may not become MS.

MS is a condition that affects the nerves that connect your brain and spinal cord. MS causes your immune system to mistakenly attack the covering of your nerve fibers. This means that your brain can’t communicate well with the rest of your body.

Some symptoms of MS may include:

It’s not known how Avonex works to ease symptoms. But it’s believed that the drug may change how your immune system works and decrease inflammation (swelling and damage). This may then help relieve your symptoms.

If you have questions about whether or not Avonex is right for you, talk with your doctor.

Like most drugs, Avonex may cause mild or serious side effects. The following lists contain some of the more common side effects that Avonex may cause. These lists don’t include all possible side effects.

Keep in mind that side effects of a drug can depend on:

  • your age
  • other health conditions you have
  • other medications you may be taking

Your doctor or pharmacist can tell you more about the potential side effects of Avonex. They can also suggest ways to help reduce side effects.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medications safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect while using Avonex and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.

Mild side effects

Here’s a list of some of the mild side effects that Avonex can cause. To learn about other mild side effects, talk with your doctor or pharmacist, or read Avonex’s prescribing information.

Mild side effects of Avonex that have been reported include:

Mild side effects of many drugs may go away within a few days or a couple of weeks. But if they become bothersome, talk with your doctor or pharmacist.

Serious side effects

Serious side effects from Avonex can occur, but they aren’t common. If you have serious side effects from Avonex, call your doctor right away. But if you think you’re having a medical emergency, you should call 911 or your local emergency number.

Serious side effects of Avonex that have been reported include:

For details about some of these side effects, see the “Side effect focus” section.

Allergic reaction

For some people, Avonex can cause an allergic reaction. But this side effect wasn’t reported in the drug’s studies.

In general, symptoms of an allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep using Avonex.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Avonex, they may have you switch to a different treatment.

Keep in mind that the caps of Avonex prefilled syringes are made from latex. If you have an allergy to latex, the auto-injector form of the drug may be a better choice for you. Talk with your doctor to learn more.

Side effect focus

Learn more about some of the side effects Avonex may cause.

Hair loss

Hair loss is a rare side effect that you may experience with Avonex. Although uncommon, hair loss was reported in studies of people using Avonex.

What might help

If you notice that you’re losing your hair when using Avonex, talk with your doctor or pharmacist. They may be able to recommend medications that you can try to help reduce your hair loss. If the hair loss is very bothersome to you, your doctor may recommend a medication other than Avonex.

Liver damage

Although rare, liver damage is a possible side effect of using Avonex. Some people who used Avonex in studies had liver function test results that may indicate liver disease. In some cases, severe liver disease has been reported in people after they’ve used Avonex.

Even though liver damage is rare with Avonex use, you should know about its symptoms. This helps you monitor for them. Symptoms may include:

  • jaundice (yellowing of your skin and whites of your eyes)
  • belly pain
  • nausea or vomiting

If you’re also taking other medications that may affect your liver, Avonex may increase your risk of liver damage.

What might help

Before you start using Avonex, be sure to tell your doctor about any other medications that you take. Your doctor should be able to help determine your risk of liver damage.

Throughout your treatment with Avonex, your doctor will monitor your liver with blood tests. If you develop any symptoms of liver damage, be sure to tell your doctor right away. If you have symptoms of liver damage or if your blood tests are showing possible liver damage, your doctor may recommend that you stop using Avonex.

Depression

Some people using Avonex developed depression, mood changes, or suicidal thoughts or behaviors during treatment. Depression was a common side effect of this medication. But reports of suicidal thoughts or behaviors were rare.

Symptoms of these side effects can include:

What might help

Before you start Avonex, tell your doctor if you have any history of depression, mood disorders, or suicidal thoughts or behaviors. They may monitor you more often than usual if you have a history of mental health conditions.

If you develop any of the symptoms mentioned, be sure to talk with your doctor or caregiver right away. In some cases of suicidal thoughts or behaviors, you may need to go to an emergency room.

Your doctor will usually have you stop Avonex treatment if you develop depression, mood changes, or suicidal thoughts or behaviors. Some people reported that their depression symptoms eased after stopping treatment with Avonex.

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

  • Call or text the 988 Suicide and Crisis Lifeline at 988 or chat at 988lifeline.org. Caring counselors are available to listen and provide free and confidential support 24/7.
  • Text HOME to the Crisis Text Line at 741741 to connect with a volunteer crisis counselor for free and confidential support 24/7.
  • Not in the United States? Find a helpline in your country with Befrienders Worldwide.
  • Call 911 or your local emergency services number if you feel safe to do so.

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you’re not in the same household, stay on the phone with them until help arrives.

Your doctor will recommend the dosage of Avonex that’s right for you. The following are commonly used dosages, but always follow the dosage your doctor prescribes.

Form and strength

Avonex is a liquid solution that you inject into the muscle of your upper outer thigh.

Avonex comes in two forms: a single-use prefilled syringe and an auto-injector pen. Each form contains 30 micrograms (mcg) of medication in 0.5 milliliters (mL) of solution.

Recommended dosage

You’ll usually inject Avonex once weekly. The dosing schedule for the drug increases over the course of a 4-week period. Your doctor will discuss your specific dosing frequency with you before your first dose.

When you first start Avonex, your doctor will usually start by prescribing a low dosage. Here’s the standard dosing for Avonex:

  • Week 1: one 7.5-mcg injection
  • Week 2: one 15-mcg injection
  • Week 3: one 22.5-mcg injection
  • Week 4 and beyond: one 30-mcg injection (this is known as the maintenance dosage)

Questions about dosing for Avonex

Here are some common questions about Avonex and its dosage.

  • What if I miss a dose of Avonex? If you miss your dose of Avonex, inject it as soon as you remember. But do not inject it if it’s almost time for your next dose. In that case, you’ll likely skip the missed dose and continue with your regular dosing schedule. If you have any questions about when to inject your next dose of Avonex after a missed dose, talk with your doctor or pharmacist. They’ll be able to recommend the best schedule for you moving forward.
  • Will I need to use Avonex long term? If Avonex works to help ease your symptoms, you’ll usually continue treatment with the drug long term.
  • How long does Avonex take to work? Avonex may begin working to help prevent a multiple sclerosis (MS) relapse as soon as you inject your first dose. (A relapse is a time of new or worsening symptoms.) But because Avonex works to help prevent relapses, you may not even notice that the drug is working. If you have questions about how to tell whether Avonex is working for you, talk with your doctor.

Your doctor will explain how you should use Avonex for multiple sclerosis (MS) and clinically isolated syndrome (CIS). They’ll also explain how much to inject and how often. Be sure to follow your doctor’s instructions. The following are commonly used dosages, but always follow the dosage your doctor prescribes.

Injecting Avonex

Avonex is a liquid solution that you inject into the muscle of your upper outer thigh.

Avonex comes in two forms: a single-use prefilled syringe and an auto-injector pen. Both devices are meant to be used only once. So, once you inject your Avonex dose, you should discard the syringe or auto-injector as directed.

Before you start using Avonex, your doctor or another healthcare professional will teach you how to use the syringe or auto-injector pen. This way, you can learn how to self-inject or have a caregiver inject the drug for you. Be sure to inject your Avonex dose exactly as your doctor prescribes.

Avonex injection sites

You’ll inject Avonex into the muscle of your upper outer thigh. You should change injection sites with each dose. This helps prevent your skin from becoming irritated or developing a severe injection site reaction. Examples include infection and death of tissue.

You should not inject your dose of Avonex into skin that’s a different color than usual or bruised. You also should not inject the drug into skin that’s broken, scarred, or infected.

Taking Avonex with other drugs

If you experience side effects from Avonex, your doctor may recommend taking certain medications before your dose to help prevent the side effects. These medications may include acetaminophen (Tylenol) and diphenhydramine (Benadryl). Taking these medications before your dose may decrease your risk of certain side effects, such as fever or flu-like symptoms.

In some cases, your doctor may recommend that you use Avonex with other medications for MS or CIS. For example, if your MS symptoms get worse during treatment, your doctor may recommend taking a steroid medication with Avonex. The steroid may help ease nerve swelling.

Talk with your doctor about your treatment for MS before starting Avonex. They’ll be able to advise you on whether or not you should take other medications with Avonex.

Whether you have health insurance or not, cost may be a factor when you’re considering Avonex. What you’ll pay for Avonex may depend on several things, such as your treatment plan and the pharmacy you use.

If you have questions about how to pay for your prescription, talk with your doctor or pharmacist. You can also visit the Avonex website to find out whether you qualify for savings programs offered by the drug manufacturer.

Find answers to some commonly asked questions about Avonex.

Are there side effects related to stopping Avonex treatment?

No, you shouldn’t experience any side effects from stopping Avonex treatment. Avonex is not known to cause symptoms of withdrawal. (These symptoms are side effects that happen when you stop a drug your body is dependent on.)

But when you stop treatment with Avonex, your symptoms of multiple sclerosis (MS) or clinically isolated syndrome (CIS) may worsen. This is because Avonex was working to help ease your symptoms. If you stop injecting the drug, it’s possible that your symptoms may get worse.

If you have any questions about possible side effects when you end Avonex treatment, talk with your doctor.

At what temperature does Avonex need to be stored? Does it need to be refrigerated?

You should store Avonex in the refrigerator at a temperature of 36°F to 46°F (2°C to 8°C). Keep the syringes or auto-injectors in their original carton so that they’re protected from light.

When you’re ready for your dose of Avonex, take the medication out of the refrigerator. You should do this about 30 minutes before your injection. Let Avonex come to room temperature before you inject it. It’s important that you do not use any other heat sources, such as a microwave, to warm up the medication.

Once you have removed Avonex from the refrigerator, you should use it within 7 days. You should not put the medication back in the refrigerator once it has come to room temperature.

You may also wonder how long Avonex can be unrefrigerated. You can keep the medication at room temperature (up to 77°F/25°C) for up to 7 days. Be sure that you do not expose Avonex to high temperatures. Doing so may make the medication less effective than usual.

If you have any questions about storing Avonex, talk with your doctor or pharmacist.

How does Avonex work?

It’s not known how Avonex works to ease symptoms of MS and CIS. But it’s believed that the drug may change how your immune system works and decrease inflammation (swelling and damage). This may then help relieve your symptoms.

For more information on how Avonex works, talk with your doctor or pharmacist.

Is weight gain or weight loss a side effect of Avonex?

No, weight gain and weight loss were not side effects that were reported in studies of people using Avonex.

But in some cases, weight change can be a symptom of other side effects of Avonex. For example, if you develop heart failure due to Avonex, you may gain weight. Changes in your thyroid is another possible side effect of Avonex. And thyroid changes may cause weight gain or weight loss.

If you notice any unexpected changes in weight while you’re using Avonex, be sure to talk with your doctor. They can help determine the cause.

Can I get a flu shot if I’m using Avonex?

According to guidelines from the American Academy of Neurology, if you have MS, you should get a flu shot each year. But if your doctor advises against it, you should not get one.

If you have more questions about flu shots while you’re using Avonex, talk with your doctor.

Avonex and Rebif are both approved to treat relapsing forms of multiple sclerosis. (With these forms, you may have new or worsening symptoms.) Both of the drugs contain the active ingredient interferon beta-1a. But even though these drugs are similar, they also have many differences.

If you’d like to know more about how these drugs compare, see this side-by-side Rebif vs. Avonex comparison. And be sure to talk with your doctor about which drug is right for you.

Both Avonex and Gilenya are used to treat the same forms of multiple sclerosis. Both drugs also contain the active drug interferon beta-1a. Avonex and Gilenya have other similarities as well as differences. This may help you and your doctor determine which is the best option for you.

To learn more about how these drugs are similar and different, see this Avonex vs. Gilenya comparison. Also, talk with your doctor about which medication they think is better for you.

Before considering treatment with Avonex, talk with your doctor about all your medications and any physical or mental health conditions you have.

Interactions

Taking medications, vaccines, foods, and other things with a certain drug can affect how the drug works. These effects are called interactions.

Before starting Avonex, be sure to tell your doctor about all medications you take, including prescription and over-the-counter types. Also, describe any vitamins, herbs, or supplements you use. Your doctor or pharmacist can tell you about any interactions these items may cause with Avonex.

Interactions with drugs or supplements

There are no known interactions between Avonex and other drugs or supplements. However, it’s still important to talk with your doctor about any other drugs or supplements that you’re taking.

Warnings

Avonex may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you use Avonex. Factors to consider include those in the following list.

  • Depression, mood disorders, or suicidal thoughts: Avonex may cause depression, mood changes, or suicidal thoughts or behaviors. If you have or had any of these mental health conditions, talk with your doctor before starting Avonex treatment. This is because Avonex may make your mental health condition worse. Your doctor may recommend monitoring you more often than usual while you use Avonex. Or they may suggest a different treatment option for you.
  • Liver problems: Avonex may cause liver damage. If you already have liver damage, Avonex may make it worse. Before using Avonex, be sure to tell your doctor about any liver problems that you have. They may monitor you more often than usual to watch for signs of liver damage. Or your doctor may recommend a different medication for you.
  • Allergic reaction: If you’ve had an allergic reaction to Avonex or any of its ingredients, including rubber latex, you should not use Avonex. Ask your doctor what other medications are better options for you.
  • Congestive heart failure or other heart problems: In rare cases, Avonex may cause heart failure. If you already have heart failure or other heart problems, using Avonex may make your heart problems worse. Your doctor may monitor your heart health more often than usual or recommend a different treatment option for you.
  • Bleeding problems or blood clots: Avonex can decrease the amount of certain blood cells in your body. This may increase your risk of bleeding or clotting. If you have or had a bleeding problem or have had blood clots, be sure to tell your doctor before using Avonex. They may monitor your blood more often than usual or recommend a different treatment option for you.
  • Low blood cell counts: If you have low blood cell counts, using Avonex may make these counts worse. Be sure to tell your doctor if you have or had low blood cell counts. They may test your blood more often than usual or recommend a different treatment option for you.
  • Autoimmune disorders, such as thyroid problems: Multiple sclerosis is an autoimmune disorder. Tell your doctor about any other autoimmune disorders you have, such as thyroid problems. Sometimes, Avonex may make other autoimmune disorders worse. Your doctor may check your symptoms more often than usual to find out whether they’re getting worse. Or they may recommend a different treatment.
  • Seizure disorders: Some people using Avonex developed seizures. If you have any seizure disorders, you may have an increased risk of seizures while using the medication. Tell your doctor if you have or had a seizure disorder. They may recommend a different treatment option for you.

Avonex and alcohol

Alcohol and Avonex may both cause liver damage. So drinking alcohol while you’re using Avonex may further increase your risk for liver damage.

Talk with your doctor about how much, if any, alcohol is safe to drink during your treatment with Avonex. If it’s hard for you to avoid alcohol, they may recommend a different treatment option for you.

Pregnancy and breastfeeding

Here’s some information on whether Avonex should be used while pregnant or breastfeeding.

Pregnancy: It is not known if Avonex is safe to use while pregnant. This is because there haven’t been any studies of the drug during pregnancy.

Other interferon beta drugs have been tested during pregnancy with mixed results. (Avonex is a kind of interferon beta drug.)

If you’re pregnant or planning to become pregnant, talk with your doctor before starting Avonex. They may recommend a different treatment option for you.

Breastfeeding: It is not known how much Avonex may pass into breast milk. It’s also not known whether the drug could affect a child who is breastfed.

If you’re breastfeeding or planning to, tell your doctor before starting Avonex treatment. They can help determine the risks and benefits of using Avonex while you’re breastfeeding. They may also recommend a different medication.

Do not use more Avonex than your doctor prescribes, as this can lead to harmful effects.

What to do in case of overdose

Call your doctor if you think you’ve used too much Avonex. You can also call 800-222-1222 to reach America’s Poison Centers or use its online resource. But if you have severe symptoms, immediately call 911 or your local emergency number. Or go to the nearest emergency room.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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