interferon

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Medications and Drugs

GENERIC NAME: interferon

BRAND NAME: Roferon-A, Intron-A, Rebetron, Alferon-N, Peg-Intron, Avonex, Betaseron, Infergen, Actimmune, Pegasys

DRUG CLASS AND MECHANISM: Interferons are a family of naturally-occurring proteins that are produced by cells of the immune system. Three classes of interferons have been identified: Alfa, beta and gamma. Each class has different effects though their activities overlap. Together, the interferons direct the immune system's attack on viruses, bacteria, tumors and other foreign substances that may invade the body. Once interferons have detected and attacked a foreign substance, they alter it by slowing, blocking, or changing its growth or function.

GENERIC: no

PRESCRIPTION: yes

PREPARATIONS: The interferons are available in vials as a prepared, premeasured solution or as a lyophilized (freeze-dried) powder with a separate diluent (mixing fluid). The combination drug, interferon alfa-2b with ribavirin (Rebetron), contains ribavirin as a separate, 200 mg capsule that is taken by mouth.

Pegylated interferon alfa-2b (Peg-Intron) and alfa-2a (Pegasys) vary from the other interferons by having molecules of polyethylene glycol (PEG) attached to them. The PEG causes the interferon to remain in the body longer and thus prolongs the effects of the interferon as well as its effectiveness.

STORAGE: All interferon preparations except for two are stored in the refrigerator 2-8°C (36-46°F) before and after mixing. Interferon alfa-2b (Intron-A) may remain at room temperature 30-35°C (86-95°F) for 7-14 days before mixing, and pegylated interferon alfa-2b may remain at room temperature 15-30°C (59-86°F) before mixing. Both of these latter interferons should be used immediately or refrigerated after mixing with the diluent.

No vial of interferon should be frozen or shaken since this can damage the interferon and make it ineffective.

PRESCRIBED FOR: Since interferons enhance the immune system in many ways, the interferons have been evaluated for effectiveness in managing many diseases that involve the immune system. For example, interferon alfa-2a (Roferon-A) is FDA-approved to treat hairy cell leukemia, AIDS-related Kaposi's sarcoma, and chronic myelogenous leukemia. In addition, there are approximately 18 other cancers, and 11 other viral infections for which interferon alfa-2a is being used or being evaluated. Still other cancers and diseases, for example, multiple sclerosis, have had trials of interferon alfa-2a without success. As new interferons are discovered, they also will be evaluated for effectiveness in managing many diseases other than those they are FDA-approved to treat.

The other interferons also have FDA-approved uses. Interferon alfa-2b is approved for the treatment of hairy cell leukemia, malignant melanoma, condylomata acuminata, AIDS-related Kaposi's sarcoma, chronic hepatitis C, and chronic hepatitis B. Ribavirin combined with interferon alfa-2b, interferon alfacon-1 (Infergen), pegylated interferon alfa-2b, or pegylated interferon alpha-2a, all are approved for the treatment of chronic hepatitis C. Interferon beta-1b (Betaseron) and interferon beta-1a (Avonex) are approved for the treatment of multiple sclerosis. Interferon alfa-n3 (Alferon-N) is approved for the treatment of genital and perianal warts caused by human papillomavirus (HPV). Interferon gamma-1B (Actimmune) is approved for the treatment of chronic granulomatous disease, and severe, malignant osteopetrosis.

DOSING: Dosing is based upon the disease being treated and the interferon being used. Therefore, wide variation in dosing exists, and doses are individualized. The interferons may be given intramuscularly, intravenously, or subcutaneously on a daily, weekly or three times a week basis.

DRUG INTERACTIONS: Interferon alfa-2a, interferon alfa-2b and interferon beta-1b may increase blood levels of zidovudine (AZT, Retrovir). While this reaction may improve zidovudine's effectiveness, it also may increase the risk of blood and liver toxicity. Therefore, the dose of zidovudine may need to be reduced by as much as 75%.

Interferon alfa-2a and interferon alfa-2b may increase the time it takes for theophylline (e.g., THEO-DUR) to be eliminated from the body. Therefore, the dose of theophylline may need to be reduced.

PREGNANCY: No adequate studies have been done in pregnant women with any of the interferons; however, the use of interferons during pregnancy is best avoided because studies in animals using doses more than 100 times the doses used in humans have shown an increased risk of spontaneous abortions.

NURSING MOTHERS: The risks of using interferons during breast-feeding is not known. Because of the potential for side effects in the infant, breast-feeding should be avoided by nursing mothers who require therapy with interferon.

SIDE EFFECTS: Flu-like symptoms following each injection (fever, chills, headache, muscle aches and pains, malaise) occur with all of the interferons. These symptoms vary from mild to severe and occur in up to half of all patients. The symptoms tend to diminish with repeated injections and may be managed with analgesics such as acetaminophen (Tylenol) and antihistamines such as diphenhydramine (Benadryl).

Tissue damage at the site of injection occurs with all of the interferons but more commonly with interferon beta-1b and pegylated interferon alfa-2b.

Depression and suicide have been reported among patients receiving interferons; however, it is unclear whether depression and suicidal thoughts are caused by the diseases being treated or the interferons themselves. Therefore, all patients receiving treatment with an interferon should be observed for the development of depression and suicidal thoughts.

Other side effects that may occur with all interferons and which may be caused by higher doses are fatigue, diarrhea, nausea, vomiting, abdominal pain, joint aches, back pain and dizziness. Still other possible side effects are anorexia, congestion, increased heart rate, confusion, low white blood cell count, low platelet count, low red blood cell count, an increase in liver enzymes, an increase in triglycerides, temporary skin rashes, mild hair loss or hair thinning, swelling (edema), cough or difficulty breathing.

Reference: FDA Prescribing Information

Last Editorial Review: 2/21/2003