Peginterferon beta-1a | Side Effects, Dosage & Uses

Generic Name:

peginterferon-beta-1a, Injectable solution

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Highlights for peginterferon-beta-1a

Injectable solution

Peginterferon beta-1a is a self-injectable multiple sclerosis medication. Your doctor will show you how to use the injection properly.


The dose is injected once every 14 days, using a pen or prefilled syringe. The injection is made under the skin (subcutaneous) in your stomach, the back of your upper arm, or your thigh.


Common side effects include flu-like symptoms, such as muscle aches, fever, tiredness, or chills. You may be able to take a pain reliever to reduce some of these symptoms.


To prevent any harm to yourself or others, you’ll need to dispose of your syringe and needles in a puncture-resistant container.


It’s important to store your medication properly in the refrigerator.


Depression, suicidal thoughts

This medication may cause depression or suicidal thoughts. Call your doctor right away if you experience:

  • feelings of hopelessness, dread, or anxiety
  • the urge to harm yourself or others

May cause liver problems

Your doctor may monitor your liver function. Be sure to tell your doctor if you experience:

  • dark-colored urine
  • light-colored stools
  • yellowing of your skin or the whites of your eyes (jaundice)
  • bleeding more easily

May decrease blood cells

In some cases, people taking this drug have had low blood cell numbers. Your doctor may do blood tests while you take this drug to check your blood cell numbers.

What is peginterferon beta-1a?

This drug is a self-injected prescription drug. It’s available in these forms: subcutaneous injectable single-dose pen and subcutaneous injectable single-dose prefilled syringe.

Why it's used

This drug is used to treat people with relapsing forms of multiple sclerosis.

More Details

How it works

It isn’t known how this drug works in people with multiple sclerosis.

Why it's used

This drug is used to treat people with relapsing forms of multiple sclerosis. It won’t cure multiple sclerosis, but it may reduce the number of disease flare-ups. Symptoms of a flare-up include:

  • muscle weakness
  • problems with coordination or balance
  • vision disturbances
  • problems with thinking and memory
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peginterferon-beta-1a Side Effects

Injectable solution

Most Common Side Effects

The most common side effects that occur with peginterferon beta-1a include:

  • flu-like symptoms, including:

    • fever
    • chills
    • headache
    • muscle and joint pains
    • tiredness
  • injection-site reactions, including:

    • redness
    • pain
    • itching
    • swelling
    • warmth
    • rash
  • nausea

  • vomiting

Serious Side Effects

If you experience any of these serious side effects, call your doctor right away. If your symptoms are potentially life threatening or if you think you’re experiencing a medical emergency, call 9-1-1.

  • severe allergic reactions. Symptoms may include:

    • itching
    • swelling of your face, eyes, lips, tongue, or throat
    • trouble breathing
    • hives
  • liver problems. Symptoms may include:

    • yellowing of your skin or the whites of your eyes (jaundice)
    • dark urine
    • tiredness
    • loss of appetite
    • stomach upset or pain
  • symptoms of a heart condition, including:

    • shortness of breath
    • fatigue and weakness
    • chest pain or irregular heart beat
    • swelling around your legs, ankles, or feet (edema)
  • depression or thoughts of hurting yourself or others

  • seizures

  • thrombotic microangiopathy. This condition usually involves a low level of platelets (cells that clot your blood) and a certain type of anemia. It can start several weeks to years after you first start taking this drug. It can even be fatal (cause death). Symptoms can include: 

    • fever
    • kidney failure
    • seizures
    • vision loss
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

This drug does not cause drowsiness.

Taking a pain or fever reducer, such as acetaminophen, on the days you take the drug can help prevent some of the drug’s common side effects.

Mild side effects may disappear within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
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peginterferon-beta-1a May Interact with Other Medications

Injectable solution

Peginterferon beta-1a may interact with other medications, herbs, or vitamins you might be taking. However, interactions with this medication aren’t well studied. Your doctor should manage all of your medications carefully. If you’re curious about how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Note: You can reduce your chances of drug interactions by having all of your prescriptions filled at the same pharmacy. That way, a pharmacist can check for possible drug interactions.

Alcohol Interaction

Peginterferon beta-1a may interact with alcohol. Drinking alcohol while taking this medication increases your risk of liver damage. Tell your doctor if you drink alcohol before taking this medication.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Drug warnings
liver problems
People with liver problems

If you have any type of liver problem, let your doctor know. Your doctor may do certain tests to decide if this drug is right for you. Your doctor may still prescribe it and carefully monitor for side effects.

People with depression, mental illness

This drug may cause depression or worsen your depression. It can also change your mood or behavior. If you have a history of depression, let your doctor know.

heart conditions
People with heart conditions

It isn’t known if this drug has a direct effect on your heart. Some people who didn’t have a history of heart problems developed heart muscle problems or heart failure after taking this medication. If you already have any type of heart problem, this drug may worsen your symptoms. Discuss your heart condition with your doctor. They may still prescribe this medication with careful monitoring.

pregnant woman
Pregnant women

This drug is a category C pregnancy drug. That means two things:

  1. Research in animals has shown adverse effects to the fetus when the mother takes the drug.
  2. There haven’t been enough studies done in humans to be certain how the drug might affect the fetus.

Speak with your doctor if you’re pregnant or plan to become pregnant. This drug should only be used during pregnancy if the potential benefit outweighs the potential risk to the fetus.

Women who are breast-feeding

This drug may pass through breast milk. Even though the amount is likely small, a breastfeeding child could potentially experience serious side effects from the drug. You and your doctor should decide if you will take the drug or breastfeed.

For children

The effectiveness and safety of this drug hasn't been established in people younger than 18 years.


Don’t take this drug again if you’ve ever had an allergic reaction to this drug, another interferon beta, or peginterferon. Taking it after already having an allergic reaction to any of these drugs could be fatal.

Symptoms of allergic reaction include:

  • trouble breathing
  • swelling of your face, eyes, lips, tongue, or throat
  • hives
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How to Take peginterferon-beta-1a (Dosage)

Injectable solution

All possible dosages and forms may not be included here. Your dose, form, and how often you take it will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What Are You Taking This Medication For?

Multiple sclerosis

Brand: Plegridy

Form: Injectable pen; injectable prefilled syringe
Strengths: 125 mcg per 0.5 mL; 63 mcg per 0.5 mL, and 94 mcg per 0.5 mL (starter pack)
Adult Dosage (ages 18-64 years)
  • The recommended dose of peginterferon beta-1a is 125 micrograms (mcg). It’s injected under your skin (subcutaneously) every 14 days.
  • The starting dose may be 63 mcg on day one. From there, the dose may be increased to 94 mcg on day 15. After that, the normal dose is 125 mcg every 14 days.
Child Dosage (ages 0-17 years)

This medicine hasn’t been studied in children and shouldn’t be used in children under the age of 18 years.

Senior Dosage (ages 65 years and older)

This medicine hasn’t been studied in adults 65 years and older.

Special Considerations

Kidney Disease: Peginterferon beta-1a is removed from your body by your kidneys. If your kidneys aren’t working properly, the amount of peginterferon beta-1a in your body may increase and cause more side effects. Your doctor may monitor you for any severe side effects.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Clinical Associate Professor, University of Illinois at Chicago College of Pharmacy

This drug comes with serious risks if you don’t take it as prescribed by your doctor.

If You Don’t Take It at All

Your multiple sclerosis can become worse over time. Multiple sclerosis is active in your body and can damage your nervous system even if you aren’t experiencing symptoms. Taking this drug can help slow the damage.

If You Skip or Miss Doses

It’s important to take all of your doses at the right time. This helps to keep the same amount of the drug in your system from day to day to get the most effective results. Missing doses or not taking it as scheduled can change the amount of the drug in your body from day to day and lessen the effect of the drug.

If You Stop Taking It

Taking this drug helps to slow the damage that multiple sclerosis does to your nervous system. Stopping the drug allows the damage to happen more quickly.

What to Do If You Miss a Dose

If you forget to take your dose, take it as soon as you can. If it’s close to the time for your next dose, skip the missed dose and go back to your normal schedule. Never try to catch up by taking two doses at once. This could result in toxic side effects.

If you’re unsure about what you should do after missing a dose, call your doctor.

How to Tell If the Drug Is Working

You may be able to tell this drug is working if you experience a decrease in multiple sclerosis flare-ups.

This drug is a long-term treatment.

Important considerations for taking this drug

Store in a refrigerator

If you don’t have a place to refrigerate this drug, you can store it for up to 30 days at room temperature: 68–77°F (20–25°C).

Don’t freeze this medication. If it freezes, throw it away.

Don’t use the medication if it looks cloudy, is leaking, or has particles floating in it.

Keep it away from light by storing it in its original box.


When traveling with your medication:

  • Always carry it with you or in your carry-on bag.
  • Don’t worry about airport X-ray machines. They can’t hurt this medication.
  • You may need to show your pharmacy’s preprinted label to identify the medication. Keep the original prescription-labeled box with you when traveling.


Taking the medication:

  • The first injection should be given under the supervision of your doctor or nurse to make sure you know how to do it properly.
  • Be sure to carefully follow the guide provided with your medication.
  • You’ll inject this drug under your skin (subcutaneously), usually into your stomach, back of your upper arm, or your thigh.
  • Always use a new prefilled pen or new, unopened single-use prefilled syringe for each injection.
  • Don’t inject into skin that’s irritated, bruised, red, infected, or scarred.
  • Wash your hands before and after your dose.
  • Before injecting, let the medication come to room temperature. Don’t heat it to bring it to room temperature.
  • Rotate sites where you inject the drug to help prevent any injection site reactions.
  • Throw the syringe away after use. Don’t use it more than once.
  • Throw away needles in a needle/sharp disposal box or puncture-resistant container.

To use this medication, you’ll need:

  • alcohol wipe
  • gauze pad
  • adhesive bandage
  • a container for throwing away used needles and pens

Clinical monitoring

Liver function: Your doctor may monitor your liver function with blood tests before and during treatment. If your liver function worsens during therapy, your doctor may decrease the dose or stop this drug.


Many insurance companies may require a prior authorization before they approve the prescription and pay for this drug.

Are there any alternatives?

There are many drugs and combinations that can treat multiple sclerosis. Some may be more suitable for you than others. Talk to your doctor about possible alternatives.

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Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on January 21, 2016

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 other 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.