Interferon Alfa, Human Recombinant
Interferon alfa-2a, Interferon alfa-2b, Interferon alfa-n3
Also known as: Roferon-A · Intron-A · Alferon N · IFN-alpha · interferon-alpha · Ro-22-8181 · Sch-30500 · rIFN-A · IFLrA · a-2-interferon
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This dose is based on body surface area (mg/m²). Convert body weight to body surface area before dosing.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Cutaneous T-cell lymphoma and severe cases of oral/cutaneous papillomas | 1.5-2 million Units/m2 | SC | 3 times weekly | — | 🌎 NA |
| Immunostimulant for adjunctive treatment of dermatologic conditions (e.g., pododermatitis, papillomas, digital keratomas) | 1000 Units | PO | once daily | — | 🌎 NA |
- Immunostimulant for adjunctive treatment of dermatologic conditions (e.g., pododermatitis, papillomas, digital keratomas): Given as 1000 Unit/mL solution
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| FeLV infection (Low dose) | 30 Units/cat | PO | daily | 7 days on, 7 days off | 🌎 NA |
| FeLV infection (High dose) | 10,000-1,000,000 Units/kg | SC | once daily | — | 🌎 NA |
| FIV infection | 30 Units/cat | PO | daily | 7 days on, 7 days off | 🌎 NA |
| Chronic FHV-1 infections (Systemic) | 30 Units/cat | PO | daily | 7 days on, 7 days off; repeat cycle | 🌎 NA |
| Chronic FHV-1 infections (Ophthalmic) | 1 drop of 25-50 Units/mL of saline in affected eye(s) | Topical | q4-6h | — | 🌎 NA |
| Acute life-threatening FHV-1 infections in kittens | 10,000 Units/kg | SC | daily | up to 3 weeks | 🌎 NA |
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Interferon alfa is a cytokine used primarily to alleviate the clinical effects of certain viral diseases and as an immunomodulator.
- In Cats: It is used via subcutaneous (SC) or oral/buccal administration to treat virus-induced diseases such as Feline Immunodeficiency Virus (FIV), Feline Leukemia Virus (FeLV), and Feline Herpesvirus-1 (FHV-1).
- In Dogs: It is used as an adjunctive treatment for viral or immunosuppression-related conditions (e.g., papillomas, pododermatitis, digital keratomas) and has been evaluated for certain neoplastic diseases like hemangiosarcoma.
Clinical Pearl: Because this is a human recombinant protein, cats given parenteral human interferon-alfa may develop significant neutralizing antibodies after 3-7 weeks of treatment, resulting in a loss of efficacy. Feline interferon-omega is often preferred in modern practice when available. Low-dose oral administration is thought to act via local oropharyngeal immunomodulation rather than systemic absorption.
Mechanism of action
Interferon alfa exhibits antiviral, antiproliferative, and immunomodulating effects.
- Mechanism: It binds to specific cell-surface receptors → activates the JAK-STAT signaling pathway → induces transcription of interferon-stimulated genes (ISGs).
- Antiviral Activity: The ISGs produce proteins (e.g., 2',5'-oligoadenylate synthetase, protein kinase R) that inhibit the synthesis of viral RNA, DNA, and cellular proteins, effectively degrading viral RNA and halting viral replication.
- Immunomodulation: Enhances macrophage phagocytic activity and augments specific cytotoxicity of lymphocytes for target cells.
Safety & warnings
Contraindications
- Feline Infectious Peritonitis (FIP) - low dose oral therapy is contraindicated
- Preexisting autoimmune disease
- Severe cardiac disease
- Severe pulmonary disease
- 'Brittle' diabetes
- CNS disorders
- Known hypersensitivity to the drug
Adverse effects
- Malaise
- Fever
- Allergic reactions
- Myelotoxicity (anemia, leukopenia, thrombocytopenia)
- Myalgia
- Neutralizing antibody formation (in cats, leading to loss of efficacy)
- Hepatotoxicity (reported in humans)
- Neurotoxicity (reported in humans)
- Flu-like syndrome (reported in humans)
Precautions
When used parenterally, carefully weigh the risks versus benefits in patients with preexisting autoimmune disease, severe cardiac or pulmonary disease, 'brittle' diabetes, Herpes infections, or CNS disorders.
- Pregnancy: Safety is not established (FDA Category C). High parenteral doses in monkeys increased abortifacient activity.
- Antibody Formation: Prolonged parenteral use in cats (3-7 weeks) often leads to neutralizing antibodies, rendering the drug ineffective.
Drug interactions
Additive or synergistic antiviral effects may occur.
Additive or synergistic antiviral effects may occur.
Increased toxicities may occur without synergistic antiviral effects.
Monitoring
- Clinical efficacy and symptom resolution
- Complete Blood Count (CBC) if used parenterally (monitor for myelotoxicity)
- Body temperature (monitor for fever)
Pharmacokinetics
Half-life
Absorption
Poorly absorbed after oral administration due to degradation by proteolytic enzymes. However, it may stimulate local lymphoid tissues via the upper GI mucosa.
Distribution
Widely distributed throughout the body, but does not penetrate the CNS well. Placental transfer is unknown.
Metabolism
Freely filtered by the glomeruli and absorbed by the renal tubules, where it is metabolized by brush border or lysosomes. Hepatic metabolism is of minor importance.
Elimination
Primarily renal.
Overdose
No specific information is available regarding acute toxicity or overdosage. Dosages should be determined and calculated carefully.
Available products
Formulations
- Injection (prefilled syringes)
- Powder for injection
- Solution for injection
Human-labeled
- Interferon Alfa-2a Injection (Roferon-A): 3 million, 6 million, 9 million I.U./syringe
- Interferon Alfa-2b Powder for Injection (Intron A): 5, 10, 18, 25, 50 million Units/vial
- Interferon Alfa-2b Injection (Intron A): 3, 5, 10 million Units/dose in multidose pens
- Interferon Alfa-2b Solution for Injection (Intron A): 3, 5, 10, 18, 25 million Units/vial
- Interferon Alfa-N3 Injection (Alferon N): 5 million Units/mL
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Commercially available products should be stored in the refrigerator; do not freeze the accompanying diluent. Do not expose solutions to room temperature for longer than 24 hours. Do not vigorously shake solutions. Diluted oral solutions can be frozen (preferably at -70°C) if a protein such as albumin is added to maintain stability; otherwise, freezing highly dilute solutions may result in a loss of activity.
Client information
This medication is often used in an 'investigational' or off-label manner in veterinary medicine.
- Expectations: Please understand that its efficacy and safety have not been definitively established for all conditions in pets.
- Administration: If you are giving this medication by mouth, it is usually a highly diluted liquid. Follow your veterinarian's exact dosing schedule (e.g., 7 days on, 7 days off).
- Storage: Proper storage is critical. Keep refrigerated or frozen exactly as instructed by your veterinarian. Do not vigorously shake the solution.
- Side Effects: Side effects are uncommon with oral use. If your pet receives injections, watch for signs of fever, lethargy, or muscle aches, and report them to your veterinarian.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.