Interferon alfa !
An injected protein that switches on antiviral defences. Once central for hepatitis B and C, it causes flu-like symptoms and depression.
Updated 2026-11-01
Also called: interferon alfa-2a, interferon alfa-2b, peginterferon alfa-2a, peginterferon alfa-2b
Mechanism of action
Interferon alfa binds the type I interferon receptor and activates the JAK-STAT pathway. A STAT complex enters the nucleus and switches on genes that create an antiviral state: 2'-5' oligoadenylate synthetase activates RNase L to cut RNA, and protein kinase R phosphorylates eIF-2 to stop protein synthesis. It also raises MHC class I expression and helps cytotoxic T cells; pegylated forms last long enough for weekly injection.
- Binds the type I interferon receptor
- Activates JAK-STAT signalling
- Switches on antiviral genes (2'-5' OAS, protein kinase R)
- Viral RNA is cut and protein synthesis blocked; immunity strengthens
Pharmacokinetics
- Absorption
- Not absorbed by mouth; injected subcutaneously, intramuscularly or intravenously
- Distribution
- Pegylation slows clearance and allows weekly injection
Indications
- Chronic hepatitis B and C (largely replaced by oral antivirals for hepatitis C) Viral hepatitis →
- AIDS-related Kaposi sarcoma Kaposi sarcoma →
- Adjuvant treatment of malignant melanoma after surgery Melanoma →
- Genital warts (condylomata acuminata) Human papillomavirus (HPV) infection →
- Hairy cell leukaemia and follicular non-Hodgkin lymphoma
Adverse effects
Common
- Flu-like symptoms: fever, chills, myalgia, headache, fatigue
- Loss of appetite and weight
- Hair loss
- Injection site reactions
Contraindications
- Hypersensitivity to interferon alfa
- With ribavirin: autoimmune hepatitis and decompensated cirrhosis
Key interactions
- Zidovudine and ribavirin
- More haematological toxicity
- Drugs with neurotoxic or cardiotoxic effects
- Interferon can increase these effects
What is monitored
- Blood count
- Thyroid function
- Liver tests
- Mood and suicidal thoughts at every visit
Administration and safety
- Injected; the route depends on the product and indication
- Injection sites are rotated
- Look-alike risk between interferon alfa, peginterferon alfa and interferon beta products
Nursing care
- Screen for depression before and during treatment
- Suggest giving injections in the evening and using fever control as prescribed for flu-like symptoms
- Teach injection technique and safe disposal of syringes
- Teach to report chest pain, breathlessness, signs of infection or bleeding
Pregnancy and breastfeeding
Safety in pregnancy is not established and it may impair fertility; with ribavirin it is contraindicated.
Test yourself
Think of the answer, then tap the question to see it.
Which intracellular pathway does interferon alfa activate?
The JAK-STAT pathway.
Which two interferon-induced proteins block viral replication?
2'-5' oligoadenylate synthetase (which activates RNase L) and protein kinase R (which phosphorylates eIF-2).
Which psychiatric effect must be screened for during interferon therapy?
Depression, including suicidal thoughts.
Which endocrine organ is checked during interferon therapy?
The thyroid (autoimmune thyroiditis, hypothyroidism).
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Interferon Alfa-2b Injection: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 63 (McGraw Hill, 2023).
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Representative model, for educational purposes only.