[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Interferons](https://durgical.com/en/pharmacology/classes/interferons/) › Interferon alfa

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# 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

- Class: [Interferons](https://durgical.com/en/pharmacology/classes/interferons/)
- Receptor: Type I interferon receptor (IFNAR1/IFNAR2)
- ATC code: L03AB05

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 →](https://durgical.com/en/conditions/viral-hepatitis/)
- AIDS-related Kaposi sarcoma [Kaposi sarcoma →](https://durgical.com/en/conditions/kaposi-sarcoma/)
- Adjuvant treatment of malignant melanoma after surgery [Melanoma →](https://durgical.com/en/conditions/melanoma/)
- Genital warts (condylomata acuminata) [Human papillomavirus (HPV) infection →](https://durgical.com/en/conditions/human-papillomavirus-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

### Serious (rare, important)

- Depression and suicidal thoughts
- Neutropenia and thrombocytopenia
- Autoimmune disease, including thyroiditis and hypothyroidism
- Ischaemic events (angina, myocardial infarction) and serious infections

## 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.

## Memory aid

Interferon alfa: «FLU-DEPRESSED-COUNT»: flu-like symptoms, depression, low blood counts (and the thyroid).

## 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).

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/interferon-alfa/)

## Related drugs

- [Interferon beta](https://durgical.com/en/pharmacology/interferon-beta/)
- [Interferon gamma](https://durgical.com/en/pharmacology/interferon-gamma/)
- [Ribavirin](https://durgical.com/en/pharmacology/ribavirin/)

## Related conditions

- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)
- [Kaposi sarcoma](https://durgical.com/en/conditions/kaposi-sarcoma/)
- [Melanoma](https://durgical.com/en/conditions/melanoma/)
- [Human papillomavirus (HPV) infection](https://durgical.com/en/conditions/human-papillomavirus-infection/)

[← Back to the class: Interferons](https://durgical.com/en/pharmacology/classes/interferons/)

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](https://medlineplus.gov/druginfo/meds/a690006.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L03AB05) (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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/interferon-alfa/