Intron A (Interferon Alfa-2b) - Injection


Alpha interferons such as interferon alfa-2b may cause or aggravate fatal or life-threatening neuropsychiatric, autoimmune, ischemic, and infectious disorders. If you have severe or worsening symptoms of these conditions, stop therapy and contact your healthcare provider.

What Is Interferon Alfa-2b?

Recombinant interferon alfa-2b is an injectable prescription medication used to treat a variety of diseases, including certain types of cancer, hepatitis B and C, and genital warts.

It is a man-made form of a protein naturally produced by the body that alerts the immune system that cells need to be destroyed, and it interferes with the reproduction of virus cells in the body.

Interferon alfa-2b is administered by injection either intramuscularly, subcutaneously (under the skin), or intralesionally (into the lesion). A healthcare provider can also give it intravenously.

Drug Facts

Generic Name: Interferon alfa-2b

Brand Name(s): Intron A (discontinued)

Drug Availability: Prescription

Administration Route: Injection

Therapeutic Classification: Immunological agent

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Interferon alfa-2b

Dosage Form(s): Powder for solution

What Is Interferon Alfa-2b Used For?

Interferon alfa-2b can be prescribed for many reasons, including:

How to Take Interferon Alfa-2b

A healthcare provider should provide you with a demonstration and instructions on how to administer interferon alfa-2b. It should be taken as prescribed by the healthcare provider. Depending upon the reason it is prescribed, it may be injected subcutaneously (just under the skin), in a muscle, or directly into genital wart lesions. Your healthcare provider will tell you how much to take and how often to take it.


Interferon alfa-2b comes in two forms:

  1. A vial with powder and a vial of sterile water that need to be mixed together immediately before use
  2. A premixed vial

Both of these forms should be stored in the refrigerator at 36 F to 46 F. Do not freeze the solution.

After mixing the vial of powder and sterile water for injection, throw away any medicine left in the vial after withdrawing one dose. Premixed vials can last for one month before you need to throw away the leftover medicine.

Off-Label Uses

Interferon alfa-2b has been prescribed off-label for reasons other than the ones listed above. Apart from its FDA-approved indications, interferon alfa-2b has also been prescribed for myeloproliferative disorders such as essential thrombocythemia, polycythemia vera, and myelofibrosis. Myeloproliferative disorders are blood disorders in which the bone marrow produces too many blood cells.

What Are the Side Effects of Interferon Alfa-2b?

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 healthcare provider. You may report side effects to the FDA at or 1-800-FDA-1088.

Common Side Effects

The most common side effects of taking interferon alfa-2b are flu-like symptoms, which usually last about one day after the injection and improve or go away after a few weeks of continued use. The symptoms include:

  • Headaches
  • Muscle aches
  • Fever
  • Fatigue or tiredness

Severe Side Effects

Call your healthcare provider immediately if you think you’re experiencing severe side effects from interferon alfa-2b. If you feel your symptoms are life-threatening, call 911, as you could be having a medical emergency. Serious side effects and their symptoms can include the following:

  • Low white blood cell and platelet counts can occur.
  • Heart problems: Signs of heart problems can include low blood pressure, abnormal heart rate, and breathing difficulties.
  • Changes in mental health status: Symptoms can include irritability, depression, aggressiveness, or suicidal thoughts or behaviors.
  • New or worsening autoimmune diseases, such as rheumatoid arthritis, lupus, psoriasis, and sarcoidosis, can occur.
  • Eye problems may lead to vision loss or blindness.
  • Thyroid dysfunction: Signs may include concentration problems, weight changes, feeling cold or hot all the time, and skin changes.
  • High blood sugar levels or diabetes: Symptoms are increased thirst or appetite, tiredness, frequent urination, weight loss, and fruity breath.
  • Lung problems may include inflammation, trouble breathing, pneumonia, or new or worse high blood pressure in the lungs.
  • Allergic reaction: Symptoms may cause wheezing, anxiousness, swelling of the face or tongue, or hives.
  • Liver problems: Symptoms may include nausea, yellowing of the skin or eyes (jaundice), appetite loss, and tiredness.
  • Inflammation of the pancreas or large intestines can cause severe stomach and back pain, nausea, vomiting, and fever.

Report Side Effects

Interferon alfa-2b 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 online or by phone (800-332-1088).

Dosage: How Much Interferon Alfa-2b Should I Take?

A trained healthcare provider will administer this injection for you in a medical setting, or you will be instructed on how to self-administer at home.

If you are self-injecting interferon alfa-2b, use it exactly as directed by your healthcare provider. Follow their instructions on how much to administer, where to inject yourself, and when to administer it.


Interferon alfa-2b may require dose modification if side effects are being experienced. Depending upon the severity of the symptoms, interferon alfa-2b may need to be temporarily stopped, or the dose strength and frequency may be adjusted.

Missed Dose

If you miss a dose of interferon alfa-2b, take it as soon as you remember, either on that same day or the next day. Tell your healthcare provider if it has been more than a day since the missed dose. Never double up on doses.

Overdose: What Happens If I Take Too Much Interferon Alfa-2b?

Potentially serious events could occur if too much interferon alfa-2b is injected in a single dose or with longer durations of treatment than prescribed. These include the potential for heart attack, liver damage, kidney failure, and bleeding.

If you are concerned that you administered too much of this medication, contact your healthcare team immediately.

What Happens If I Overdose on Interferon Alfa-2b?

If you think you or someone else may have overdosed on interferon alfa-2b, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking interferon alfa-2b, call 911 immediately.


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

Using interferon alfa-2b injection 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 required for women who are of childbearing age before starting combination therapy with interferon alfa-2b injection and ribavirin. Female patients and female partners of male patients must use 2 forms of birth control during therapy and for 6 months after therapy ends. Female patients must have regular pregnancy tests during combination therapy.

This medicine may cause serious types of allergic reactions, including anaphylaxis. Anaphylaxis can be life-threatening and requires immediate medical attention. Call your doctor right away if you have itching, hives, hoarseness, trouble breathing, trouble swallowing, or any swelling of your hands, face, mouth, or throat.

Interferon alfa-2b injection can temporarily lower the number of white blood cells in your blood, increasing 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.

This medicine can increase thoughts of suicide in people with or without a history of a mental illness. This medicine may also cause relapse in people with a history of substance abuse. Tell your doctor right away if you start to feel more depressed or exhibit aggressive behavior. Also tell your doctor right away if you have thoughts of hurting yourself or others. Report any unusual thoughts or behaviors that trouble you, especially if they are new or get worse quickly. Make sure your caregiver knows if you have trouble sleeping, get upset easily, have a big increase in energy, or start to act reckless. Also tell your doctor if you have sudden or strong feelings, such as feeling nervous, angry, restless, violent, or scared. If you, your child, or your caregiver notice any of these side effects during treatment and up to 6 months after treatment, tell your doctor right away.

The powder form of this medicine contains albumin, which comes from human blood. Some human blood products have transmitted certain viruses to people who have received them, although the risk is low. Human donors and donated blood are both tested for viruses to keep the transmission risk low. Talk with your doctor about this risk if you have questions.

Check with your doctor if blurred vision, decreased vision, or any other change in vision occurs during your treatment. Your doctor may want you to have your eyes checked by an ophthalmologist (eye doctor).

Check with your doctor right away if you have pain or tenderness in the upper stomach, pale stools, dark urine, loss of appetite, nausea, unusual tiredness or weakness, or yellow eyes or skin. These could be symptoms of a serious liver problem.

This medicine may make you tired or unable to concentrate. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.

Interferon alfa-2b injection and ribavirin combination may cause a dry mouth. For temporary relief of mouth dryness, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

Some patients who have used this medicine with ribavirin have had vomiting. If you vomit during or after your treatment, rinse your mouth out with water. This may also help prevent damage to your teeth and gums.

Children who use interferon alfa-2b and ribavirin combination may have weight loss and slowed growth. Most children have a growth spurt and gain weight after therapy ends. If you have questions about this, talk to your doctor.

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 Interferon Alfa-2b?

Interferon alfa-2b should not be used in people who:

  • Have an allergy or sensitivity to interferon alfa-2b or any of its ingredients
  • Have autoimmune hepatitis or severe liver disease
  • Are pregnant

What Other Medications Interact With Interferon Alfa-2b?

Use caution when taking any other medications that cause suppression of the bone marrow, such as Retrovir (zidovudine). The combination can cause severely decreased blood cells.

If you are also taking a medication called theophylline (brand names such as Quibron-T, Theolair, Uniphyl, and others) dose reductions in the theophylline may be required, as the use of interferon alfa-2b can increase levels of the drug in the body.

What Medications Are Similar?

A medication similar to interferon alfa-2b is pegylated interferon alfa. This medication has the same active ingredient as interferon alfa-2b but also contains polyethylene glycol. This combination allows the interferon to stay in the body longer and provides an extended duration for treating the disease for which it is prescribed. It should not be taken along with interferon alfa-2b.

Frequently Asked Questions

  • What is interferon alfa-2b used for?

    Interferon alfa-2b is prescribed for several different health conditions, such as hairy cell leukemia, malignant melanoma, follicular lymphoma, genital warts, AIDS-related Kaposi's sarcoma, chronic hepatitis C, and chronic hepatitis B.

  • How does interferon alfa-2b work?

    Interferon alfa-2b works by stimulating the immune system to attack the cells responsible for the cancer or to help treat other diseases such as hepatitis and genital warts.

  • What are the side effects of interferon alfa-2b?

    The more common side effects of interferon alfa-2b are flu-like symptoms, such as fever, muscle aches, headaches, and fatigue. Injection site reactions can also occur. In severe cases, interferon alfa-2b can cause mental health changes, vision loss, decreased blood cell counts, new or worsening autoimmune diseases, dysfunctional thyroid, and more. Tell your healthcare provider if you experience any new or worrisome side effects.

How Can I Stay Healthy While Taking Interferon Alfa-2b?

Taking interferon alfa-2b can come with a potentially long list of side effects, but keep in mind that just because a side effect is listed doesn’t mean you will experience it. Tell your healthcare provider of any new or worsening side effects as soon as possible so that they can help you manage them. You can reduce the flu-like symptoms by injecting this medication at bedtime and using a fever reducer or pain reliever such as acetaminophen before each dose. In some cases, dosage adjustments or temporarily stopping the medication may be necessary.

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.

4 Sources
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.
  1. DailyMed. Label: Intron A- interferon alfa-2b kit, Intron A- interferon alfa-2b injection, solution.

  2. Merck. Intron A medication guide.

  3. How J, Hobbs G. Use of interferon alfa in the treatment of myeloproliferative neoplasms: perspectives and review of the literature. Cancers (Basel). 2020;12(7):1954. doi:10.3390/cancers12071954

  4. MedlinePlus. Peginterferon alfa-2b (PEG-Intron).

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.