Interferon Omega
Recombinant Omega Interferon of Feline Origin, rFelFN-w
Also known as: Virbagen Omega · interferon-w · IFN-w (feline recombinant) · rFelFN-w · rFeIFN-omega · Feline interferon omega
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
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 |
|---|---|---|---|---|---|
| Treatment of parvovirus (enteric form) | 2.5 million Units/kg IV once daily | IV | q24h | 3 days | 🌎 NA |
| Treatment of atopic dermatitis | Dogs 8-15 kg = 1 million Units; 15-29 kg = 2 million Units; 29-40 kg = 3 million Units; >40 kg = 4 million Units | SC | Specific days | Days 0, 3, 7, 14, 21, 35, 56, 90, 120, & 150 | 🌎 NA |
| Parvovirus | 2.5 million units/kg | IV | q24h | 3 days | 🌍 EU |
- Treatment of parvovirus (enteric form): The earlier the dog is treated, the more likely of success.
- Treatment of atopic dermatitis: Further larger-scale studies needed to confirm cost-effectiveness and safety for long-term treatment.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of FeLV and/or FIV (non-terminal clinical stages) | 1 million Units/kg SC once daily | SC | q24h | 5 days (Three separate 5-day treatments performed at day 0, day 14, and day 60) | 🌎 NA |
| FHV-1 facial dermatitis | Day 0: 1.5 million Units/kg (half peri-lesionally/intradermally, half SC). Day 2 and 9: 1.5 million Units/kg SC. Days 19, 21, and 23: 0.75 million Units/kg peri-lesionally/intradermally + 0.75 million Units/kg SC. | SC / Intradermal / Peri-lesional | Specific days | 23 days | 🌎 NA |
- FHV-1 facial dermatitis: Cat was sedated with propofol for peri-lesional and intradermal injections.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Interferon-omega is a recombinant type I interferon of feline origin. It acts as a potent immunomodulator and antiviral agent.
- Veterinary Use: It is primarily utilized in veterinary medicine for the treatment of severe viral infections, notably canine parvovirus and feline retroviruses (FeLV and FIV).
- Cross-Species Efficacy: Clinical Pearl: Although it is a feline-origin protein, it is highly effective in dogs because type I interferons share cross-species receptor affinity. However, prolonged use in dogs may lead to the formation of neutralizing antibodies.
- Emerging Uses: It has shown potential benefits in treating canine atopic dermatitis, feline infectious peritonitis (FIP), feline calicivirus (FCV), and feline herpesvirus (FHV-1) dermatitis or keratitis.
- Availability: It is commercially available in the EU and other regions but is not commercially available in the USA (requires legal importation for compassionate use).
Mechanism of action
Interferon-omega does not act as a direct virucidal agent. Instead, it induces an antiviral state in host cells:
- Receptor Binding: Binds to specific type I interferon receptors on the surface of target cells.
- Signal Transduction: Activates the JAK-STAT signaling pathway.
- Gene Transcription: Induces the transcription of interferon-stimulated genes (ISGs).
- Antiviral Proteins: Leads to the production of key enzymes such as 2'-5' oligoadenylate synthetase (OAS) and protein kinase R (PKR).
- Viral Inhibition: These enzymes inhibit viral mRNA translation and degrade viral RNA → effectively halting viral replication.
Additionally, it nonspecifically enhances host immune defense mechanisms by stimulating natural killer (NK) cells and macrophages.
Safety & warnings
Contraindications
- Concurrent vaccination in dogs (wait until fully recovered)
- Vaccination in cats during and after treatment (due to the immunosuppressive nature of FeLV/FIV)
- Substitution with human interferons (alpha, beta, or gamma)
- No specific contraindications available in the monograph
Adverse effects
- Hyperthermia (typically 3-6 hours post-dose)
- Vomiting
- Soft feces or mild diarrhea (cats)
- Transient fatigue or lethargy (cats)
- Slight decreases in RBCs, WBCs, and platelets (usually resolves within a week)
- Increased ALT (usually resolves within a week)
- Antibody formation in dogs (with prolonged or repeated treatment)
- Mild diarrhoea
- Decreased WBCs (leukopenia)
- Decreased platelets (thrombocytopenia)
- Decreased RBCs (anaemia)
- Increased liver enzyme activities
- Ocular irritation (with topical use in cats)
- Immune-mediated diseases (reported with long-term administration in humans)
Precautions
Do not vaccinate dogs currently being treated until they have fully recovered. Cat vaccinations are contraindicated during and after treatment due to the underlying immunosuppressive retroviral infections. Intravenous administration in cats may cause an increased incidence and severity of adverse effects, though adverse effects in cats are generally uncommon. Dogs may develop neutralizing antibodies if treatment is prolonged beyond the labeled dosage period.
Drug interactions
May increase the risk of liver toxicity; use with caution.
May increase the risk of bone marrow suppression; use with caution.
Should not be administered concurrently until the animal has clinically recovered.
Improves prognosis; no negative interactions observed.
Improves prognosis; no negative interactions observed.
Monitoring
- Clinical efficacy (resolution of viral infection signs)
- Complete Blood Count (CBC) to monitor for myelosuppression
- Hepatic function tests (ALT)
- Complete Blood Count (WBCs, RBCs, platelets)
- Liver enzyme activities
- Body temperature
- Clinical signs of gastrointestinal upset or fatigue
Pharmacokinetics
Half-life
Absorption
Rapidly bound to specific receptor sites on a variety of cells after intravenous injection.
Distribution
Highest tissue levels are found in the liver and kidneys. In dogs, volume of distribution (Vd) at steady state is about 0.1 L/kg.
Metabolism
Catabolized in the kidneys.
Elimination
Filtered in the renal glomeruli. Total body clearance in dogs is 6.9 mL/min/kg.
Overdose
In safety studies, 10X overdoses in dogs and cats caused mild lethargy/somnolence, slight hyperthermia, and slight increases in respiratory and heart rates. In all animals tested, clinical signs resolved within 7 days and no specific treatment was required.
Available products
Formulations
- Lyophilized powder for injection: 10 million Units/vial
- Lyophilized powder for injection: 5 million Units/vial
- 10 million units/vial powder with solvent for reconstitution
Veterinary
- Virbagen Omega 10 million Units/vial
- Virbagen Omega 5 million Units/vial
Regulatory status
Authorized for veterinary use in the EU.
POM-V classification.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in its original carton in the refrigerator (4°C ± 2°C) and protect from freezing. Shelf life is 2 years when properly stored. Once reconstituted with the supplied isotonic sodium chloride solution, it contains no preservatives and should ideally be used immediately; however, the reconstituted solution is reported to be stable for at least 3 weeks when refrigerated. Do not mix with any other vaccine or immunological product.
Client information
Important Note: This medication is typically administered in a veterinary hospital setting where your pet can be closely monitored and supported, especially since it is often used for severe viral infections like Parvovirus.
- What to Expect: Your pet may develop a mild fever 3 to 6 hours after the injection. This is a normal immune response to the medication. Mild vomiting, tiredness, or soft stool may also occur.
- Vaccinations: Do not have your pet vaccinated while they are receiving this treatment. For cats with FeLV or FIV, vaccinations are generally not recommended even after treatment due to their compromised immune systems.
- Cost: Treatment with Interferon-Omega involves advanced recombinant technology and can be very expensive. Discuss the expected costs and prognosis with 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.