Pegasys (Peginterferon Alfa-2a) - Subcutaneous

Warning:

The United States Food and Drug Administration (FDA) has issued a boxed warning for Pegasys. Boxed warnings are the agency’s strongest warnings for serious and potentially life-threatening risks. Review these warnings and discuss your concerns with your healthcare provider before starting treatment.

The boxed warning:

  • The risk of serious disorders may cause or worsen fatal or life-threatening psychiatric, autoimmune, ischemic (reduced blood flow), and infectious disorders. Monitor closely and stop therapy following any severe or worsening signs or symptoms of the above disorders.

What Is Pegasys?

Pegasys (peginterferon alfa-a) is a prescription medication administered via a subcutaneous (under the skin) liquid injection that is used as an antiviral drug treatment for chronic hepatitis B (CHB) and hepatitis C (CHC) in both children and adults to treat compensated liver disease (cirrhosis of the liver) with the hope of clearing of the virus from the body.

Pegasys is a combination of interferon and polyethylene glycol. The term “interferon” refers to signaling proteins that are naturally produced by healthy cells in the body to fight infection and other diseases.

Typically, a virus-infected cell will release interferons causing cells to strengthen their anti-viral defenses. Pegasys is a special type of interferon that has been chemically modified to last longer in your body and does not require as frequent dosing.

“Polyethylene glycol” refers to a polyether compound (meaning a group of organic substances) made from petroleum with various pharmaceutical applications.

As a result, Pegasys works by decreasing the amount of hepatitis virus in the body to help your body's natural defense (the immune system) fight the infection.

Pegasys is available by prescription as an injectable liquid from a vial, prefilled syringe, and a disposable autoinjector.

Drug Facts

Generic Name: Peginterferon alfa-2a

Brand Name: Pegasys

Drug Availability: Prescription 

Therapeutic Classification: Antineoplastic agent

Available Generically: Yes

Controlled Substance: No

Administration Route: Subcutaneous injection 

Active Ingredient: Peginterferon alfa-2a

Dosage: Subcutaneous injection

What Is Pegasys Used For?

The Food and Drug Administration (FDA) has approved Pegasys (peginterferon alfa-a) for the treatment of CHB and CHC where the goal of treatment is to permanently rid the body of the virus, subsequently preventing the complications of chronic viral hepatitis.

Pegasys treats CHC in adults through combination therapy with other hepatitis C virus (HCV) drugs for adults with compensated liver disease. Pegasys monotherapy (meaning no added drugs) is prescribed only if the person has an intolerance to other HCV drugs. For children, Pegasys treats CHC in tandem with the drug ribavirin for pediatric individuals 5 years and older who have compensated liver disease.

Meanwhile, Pegasys treats CHB in adults who have compensated liver disease alongside evidence of viral replication and liver inflammation. For children, expect Pegasys to be prescribed to treat CHB when there is evidence of viral replication and elevations in serum alanine aminotransferase (ALT) levels (ALT is a liver enzyme).

It's important to understand that CHB and CHC are viral infections affecting the liver, and each is caused by a different virus. CHB is transmitted when blood, semen, or other body fluids from a person infected with the virus enters the body of someone who is not infected. Comparatively, CHC is spread primarily by contact with contaminated blood.

Some individuals with CHB and CHC infections can clear the infection independently, therefore not meeting the criteria to be defined as chronic or long-term, a status that may result in the need for a liver transplant.

How to Take Pegasys

Take Pegasys exactly as prescribed by your healthcare provider. It is administered as a subcutaneous injection. The usual dose in adults is 180 micrograms (μg) per week. The duration of treatment depends on what virus you are being treated for (CHB or CHC) and other factors. For children, the Pegasys dose is calculated based on your child’s body size.

Pegasys, a liquid is supplied in single-dose vials, prefilled syringes, or in an autoinjector device. Your prescribing provider will show you how to measure and inject your dose. If you are getting the single dose vial from the pharmacy, ask the pharmacist for the syringe and needle you will need to prepare and take your dose.

If you will be injecting a child, ask for a special syringe called a tuberculin syringe, which can measure out very small doses. Don’t reuse single-dose vials, prefilled syringes, needles, or autoinjectors.

Storage

Pegasys should be stored in a refrigerated area, between 36 F to 46 F. You should not freeze it, shake it, or leave the medication out of the refrigerator for more than 24 hours. Pegasys should also be protected from sources of harsh light. Like all medications, Pegasys should be kept out of the reach of children and pets.

Off-Label Uses

Pegasys is FDA approved for the treatment of CHC and CHB in adults and children. Sometimes, however, healthcare providers prescribe medications “off-label” for conditions not specifically mentioned on the product label. 

In addition to its activity against viruses, Pegasys also has some anti-cancer properties and may be used off-label to treat myeloproliferative neoplasms, a certain class of bone marrow cancer (known as multiple myeloma). Specific examples of myeloproliferative neoplasms include polycythemia vera, essential thrombocytosis, and myelofibrosis.

How Long Does Pegasys Take to Work?

Maximum serum concentration (meaning bodily absorption) of Pegasys has been studied to occur typically 72 to 96 hours post-dose. However, this time may vary depending on the volume of dosage, age, weight, or other factors. Be sure to speak with your healthcare provider to confirm when the effects of Pegasys will first occur.

What Are the Side Effects of Pegasys?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your pharmacist or a healthcare provider. You may report side effects to the FDA at fda.gov/medwatch or 1-800-FDA-1088. 

As with all medications, Pegasys can cause side effects. Tell your healthcare provider about any side effects you experience while taking this medication.

Common Side Effects

People should be aware that side effects from Pegasys can be significant and that flu-like symptoms are common in adults and kids on treatment.

The most common side effects of Pegasys are:

Severe Side Effects

The United States Food and Drug Administration (FDA) has issued a boxed warning for Pegasys. Boxed warnings are the agency’s strongest warnings for serious and potentially life-threatening risks. Review these warnings and discuss your concerns with your healthcare provider before starting treatment.

The boxed warning:

The risk of serious disorders may cause or worsen fatal or life-threatening psychiatric, autoimmune, ischemic (reduced blood flow), and infectious disorders. Monitor closely and stop therapy following any severe or worsening signs or symptoms of the above disorders.

Pegasys has some serious side effects that you should know about, and if not addressed, it could cause severe illness or even death. Usually, the side effects of Pegasys resolve after therapy is stopped.

Potential serious side effects caused by Pegasys may include:

  • Psychiatric (mental health) problems: Mood swings such as irritability, anxiety, major depressive disorder (depression), or aggressive behavior. People struggling with addiction may find that their struggles get worse. In severe cases, people may develop thoughts of suicide. If you have any of these symptoms while on therapy, especially thoughts of hurting yourself, seek help immediately. Some people develop psychiatric symptoms during therapy, and depression may require a change in dose.
  • Myocardial disruptions: Heart palpitations (fast heartbeat), angina (chest pain), or dyspnea (trouble breathing) may occur. Pegasys can also cause stroke in some people, and you should watch out for symptoms such as weakness, loss of coordination, or loss of feeling. 
  • New or worsening autoimmune symptoms: Autoimmune diseases are conditions in which your body’s immune system attacks your own body tissues. Examples of autoimmune diseases include rheumatoid arthritis, lupus, or psoriasis.

Report Side Effects

Pegasys may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Pegasys Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For injection dosage form (solution):
    • For hepatitis B:
      • Adults—Dose is based on body weight and must be determined by your doctor. It is usually 180 micrograms (mcg) injected under the skin once a week for 48 weeks. The medicine should be used on the same day each week and at about the same time.
      • Children 3 years of age and older—Dose is based on body weight or body size and must be determined by your doctor. It is usually not more than 180 mcg injected under the skin once a week (same time and day each week) for 48 weeks. The length of time will be determined by your doctor.
      • Children younger than 3 years of age—Use and dose must be determined by your doctor.
    • For hepatitis C:
      • Adults—Dose is based on body weight and must be determined by your doctor. It is usually 180 micrograms (mcg) injected under the skin once a week for 48 weeks. The medicine should be used on the same day each week and at about the same time.
      • Children—Use and dose must be determined by your doctor.
    • For hepatitis C infection, in combination with ribavirin:
      • Adults—Dose is based on body weight and must be determined by your doctor. It is usually 180 micrograms (mcg) injected under the skin once a week (same time and day each week) together with oral ribavirin twice daily for 24 to 48 weeks. The length of time will be determined by your doctor.
      • Children 5 years of age and older—Dose is based on body weight or body size and must be determined by your doctor. It is usually 180 mcg injected under the skin once a week (same time and day each week) together with oral ribavirin twice daily for 24 to 48 weeks. The length of time will be determined by your doctor.
      • Children younger than 5 years of age—Use and dose must be determined by your doctor.

Modifications

Before beginning Pegasys, users should be aware of the following:

Severe allergic reaction: Avoid using Pegasys if you have a known allergy to it or any of its ingredients. Ask your pharmacist or healthcare provider for a complete list of the ingredients if you're unsure.

Pregnancy: ​​In the context of combination treatment, Pegasys is not prescribed alongside another hepatitis drug, ribavirin, due to the possibility of serious side effects. Consult with a healthcare provider if you plan on becoming pregnant during your use of Pegasys, as there stand potential risks for the unborn fetus.

Breastfeeding: Caution is recommended with breastfeeding as there are limited data available on its effects. Talk with your healthcare provider if you plan to breastfeed, and weigh the benefits and risks of taking Pegasys while nursing and the different ways to feed your baby.

Adults over 65: People over 65 years may experience more pronounced cardiac-related and flu-like side effects associated with Pegasys use.

Pediatrics: Safety and efficacy in CHC pediatric people less than 5 years old and CHB pediatric people less than 3 years old have not been established. Therefore, consult a healthcare provider before starting your young child on Pegasys. 

Alcohol/smoking: Drinking and smoking can lower the effectiveness of Pegasys and potentially exasperate existing side effects. Try to stop smoking and drinking alcohol before starting Pegasys, and avoid consumption while taking the medication. Your healthcare provider can help you with this goal.

Keep in mind that your Pegasys prescription may have to be changed if you have severe kidney disease. Also, if you develop severe changes in your liver function tests during therapy, your dose may have to be changed or treatment stopped altogether.

Your blood counts (such as white blood cells and platelets) will be monitored during therapy, and certain decreases in these levels may require dose modification or discontinuation of therapy.

Missed Dose

If you miss your scheduled dose and are less than two days late, take your dose as soon as you remember. If you are more than two days late, ask your healthcare provider for further instructions.

Overdose: What Happens If I Use Too Much Pegasys?

Do not take more Pegasys than directed on the package label. If you take too much Pegasys, call your healthcare provider right away. Blood tests may be required.

While studies on Pegasys overdose are limited, the medication can spark an increased dependency on previously abused substances, in addition to the possibility of mental health lapses or depression, leading to a potential overdose. As a result, it’s important to make your healthcare provider aware of your history relating to mental health and substance abuse before starting Pegasys.

What Happens If I Overdose on Pegasys

If you think you or someone else may have overdosed on Pegasys, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Pegasys, call 911 immediately.

Precautions

Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly. Blood tests may be needed to check for unwanted effects.

Using this medicine together with ribavirin while you are pregnant can harm your unborn baby. These medicines may also cause birth defects if the father is using it when his sexual partner becomes pregnant. If a pregnancy occurs while you are using these medicines, tell your doctor right away.

A negative pregnancy test is needed for women who are of childbearing age before starting treatment with this medicine and ribavirin. Effective birth control must be used by male and female patients during treatment and for 6 months after the last dose. Female patients will need to have pregnancy tests every month during treatment and for 6 months after the last dose.

This medicine may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you, your child, or your caregiver notice any of these side effects, tell your doctor right away.

This medicine may cause serious allergic reactions, including anaphylaxis or angioedema. These can be life-threatening and require immediate medical attention. Call your doctor right away if you have itching, hives, hoarseness, trouble with breathing, trouble with swallowing, or any swelling of the hands, face, or mouth while you are using this medicine.

Serious skin reactions can occur with this medicine. Check with your doctor right away if you have blistering, peeling, or loosening of the skin, fever or chills, hives or welts, red skin lesions, a severe skin rash or acne, or sores or ulcers on the skin while you are using this medicine.

This medicine will not keep you from giving hepatitis B or hepatitis C to other people.

This medicine combined with ribavirin can temporarily lower the number of white blood cells in your blood, which will increase the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

  • If you can, avoid people with infections. Check with your doctor immediately if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
  • Check with your doctor immediately if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin.
  • Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
  • Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.
  • Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
  • Avoid contact sports or other situations where bruising or injury could occur.

Check with your doctor right away if you or your child have back, leg, or stomach pains, bleeding gums, chills, dark urine, difficulty breathing, fever, general body swelling, headache, loss of appetite, nausea or vomiting, nosebleeds, pale skin, sore throat, unusual tiredness or weakness, or yellowing of the eyes or skin. These could be symptoms of a blood disorder called hemolytic anemia.

Check with your doctor right away if you have sudden and severe stomach pain, chills, constipation, nausea, vomiting, fever, or lightheadedness. These could be symptoms of pancreatitis.

Check with your doctor right away if you have vision changes, such as blurred vision, difficulty reading, or eye pain during or after treatment. This could be symptoms of a serious eye problem. Your doctor may want an eye doctor (ophthalmologist) to check your eyes.

Peginterferon alfa-2a used together with ribavirin may affect your child's growth. Your doctor may need to check your child's height and weight during and after treatment with these medicines.

This medicine may cause some people to become drowsy, dizzy, or less alert than they are normally. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn't Take Pegasys?

Pegasys is not appropriate for everyone. You should not take this medication if you are allergic to acetaminophen or any of the inactive ingredients in Pegasys.

Pegasys may be used with caution in some people only if the healthcare provider determines it is safe. This includes:

  • You should not take Pegasys if you are allergic to peginterferon alfa-a or any ingredients of Pegasys.
  • Pegasys as monotherapy is also only prescribed if the person has significant intolerance to other hepatitis medications. Known hypersensitivity reactions such as urticaria (hives), angioedema (swelling under the skin that occurs when fluid leaks from blood vessels), bronchoconstriction (difficulty breathing), and anaphylaxis (a severe allergic reaction) to interferons or any ingredient of Pegasys will result in a healthcare provider not recommending the drug.
  • Pegasys can also harm unborn fetuses, and you should not take it if you are pregnant or plan to get pregnant during or within six months of treatment.
  • If you are a man, you should not take Pegasys if you have a female sexual partner who is pregnant or plans to become pregnant during therapy or within six months after the end of therapy.
  • Because it is not prescribed for neonates/infants, users should know that Pegasys can be used under certain circumstances in children as young as 3 years of age but should not be given to children under 1 year old, as it can be fatal.
  • People with autoimmune hepatitis or severe liver failure should also not take Pegasys.

What Other Medications May Interact With Pegasys?

Tell your healthcare provider about all of the medicines you take, including prescription and over-the-counter (OTC) medicines, and vitamins or supplements. 

Pegasys interferes with the activity of an enzyme in the liver called CYP1A2, a member of the cytochrome P450 enzyme family. This is important because several drugs are processed by the CYP1A2 enzyme and can thus interact with Pegasys. Examples include theophylline (used to treat asthma) and Clozaril (clozapine) (used to treat schizophrenia).

Pegasys can increase the potency of methadone (a drug used for pain relief), so people taking this combination should be monitored carefully. Taking Pegasys with ZDV (zidovudine) (an HIV drug) can cause decreases in blood cell counts.

Pegasys is often given in combination with a class of drugs called nucleoside analogues (a class of antiviral drugs), which act against hepatitis b virus (HBV) and the hepatitis C virus (HCV). Although this combination has proved useful in treating hepatitis, the combination can also result in increased side effects related to the nucleoside analogues. If this happens, your doses may need to be reduced.

What Medications Are Similar?

Important to understand in the makeup of Pegasys, interferon is a type of molecule produced by cells in the body to fight off infection. Your body makes different types of interferons (alpha, beta, and gamma) that serve slightly different functions. Healthcare providers have been using interferon medications for some time to treat chronic hepatitis, but other types of interferons can be used for the treatment of other viral or autoimmune diseases.

While interferons work by stimulating the immune system to fight off infection, these new drugs directly target viral molecules that are important for viral reproduction.

 Examples of these new drugs include:

Because of their less severe side effects, these new types of drugs have come to the forefront of therapy for chronic viral hepatitis, though interferon-based regimens still have their place.

When interferon is used, it is usually not given alone but with other antiviral drugs such as ribavirin.

Frequently Asked Questions

  • What is Pegasys used for?

    Pegasys (peginterferon alfa-a) is used for the treatment of chronic hepatitis B (CHB) and C (CHC) infection. CHB and CHC are viral infections that affect the liver, and each is caused by a different virus. Some people with hepatitis B and C infections are able to clear the infection on their own.

  • How does Pegasys work?

    Pegasys is a specially modified type of interferon. Interferons are special molecules produced by the immune system to stimulate immune cells to fight off certain types of infections. Interferons can be used by healthcare providers to treat viral infections (such as viral hepatitis) and autoimmune diseases.

  • What are the side effects of Pegasys?

    Side effects from Pegasys can be significant, and flu-like symptoms are common. These include fatigue, fevers, body aches, and headaches.

     Pegasys is associated with some serious side effects that can cause serious illness or even death if not addressed. These include psychiatric (mental health) problems, heart problems, stroke, or autoimmune diseases. Tell your healthcare provider immediately if you experience any of these symptoms.

How Can I Stay Healthy While Taking Pegasys?

Pegasys therapy can be difficult. Flu-like symptoms are common, and healthcare providers must watch you carefully for the development of more serious side effects. Maintain open lines of communication with your healthcare providers, so that they can be on top of any side effects which may develop.

Therapy for chronic viral hepatitis has rapidly evolved over the past few decades, and many treatment regimens are available, many of which have fewer side effects. Remember, people do best when they can advocate for themselves. Don’t be afraid to ask your healthcare providers about the availability of other therapies. 

Also, don’t be afraid to ask about non-pharmaceutical measures which may help, such as acupuncture or an exercise program. Your healthcare provider may also be aware of support groups for people living with chronic liver disease.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Rony Kampalath, MD
Rony Kampalath, MD, is board-certified in diagnostic radiology and previously worked as a primary care physician. He is an assistant professor at the University of California at Irvine Medical Center, where he also practices. Within the practice of radiology, he specializes in abdominal imaging.