Oseltamivir
Oseltamivir phosphate
Also known as: Tamiflu · GS-4104/002 · Ro-640796/002
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 |
|---|---|---|---|---|---|
| Adjunctive treatment of canine parvovirus enteritis | 2.2 mg/kg PO q12h | PO | q12h | — | 🌎 NA |
| Adjunctive treatment of canine parvovirus enteritis | 2.2 mg/kg PO twice daily for 5 days | PO | q12h | 5 days | 🌎 NA |
- Adjunctive treatment of canine parvovirus enteritis: Should be administered as early as possible in the course of the disease. More data is needed to prove efficacy.
- Adjunctive treatment of canine parvovirus enteritis: To better insure that a vomiting patient will keep the drug down, recommend administering it 30 minutes after a chlorpromazine or other antiemetic injection.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of equine Influenza A | 2 mg/kg PO twice daily for 5 days | PO | q12h | 5 days | 🌎 NA |
- Treatment of equine Influenza A: Must be given early in the course of the disease to obtain satisfactory outcome. Dose based on human pediatric dosage.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Oseltamivir is a neuraminidase inhibitor antiviral primarily developed for the treatment and prophylaxis of Influenza A and B viruses in humans.
In veterinary medicine, its use is highly controversial and largely experimental:
- Canine Parvovirus (CPV): Anecdotally and in limited studies, it has been used as an adjunctive treatment for parvoviral enteritis. While it does not directly kill the parvovirus, it is theorized to reduce the virus's ability to penetrate the intestinal mucin layer and decrease secondary bacterial translocation.
- Equine Influenza: Experimental studies have shown some efficacy in attenuating clinical signs, viral shedding, and secondary bacterial pneumonia when administered early.
Public Health Warning: Because oseltamivir (Tamiflu®) is a critical first-line defense for human influenza pandemics (e.g., H5N1), its use in veterinary patients is strongly discouraged by many experts (including the UC-Davis Koret Shelter Medicine Program) to preserve drug supplies and prevent the development of viral resistance.
Regulatory Note: The FDA has strictly banned the extra-label use of oseltamivir and other influenza antivirals in chickens, turkeys, and ducks.
Mechanism of action
Oseltamivir phosphate is a prodrug that is rapidly converted by hepatic esterases into its active metabolite, oseltamivir carboxylate.
- Antiviral Action: It competitively inhibits the viral neuraminidase enzyme → prevents the cleavage of sialic acid residues on the host cell surface → halts the release of newly formed viral particles from infected cells and prevents viral aggregation.
- Parvovirus Mechanism (Theoretical): Canine parvovirus does not possess neuraminidase. However, oseltamivir may inhibit host or bacterial neuraminidases in the GI tract → preserves the protective intestinal mucous layer → limits the ability of CPV to infect intestinal crypt cells and reduces GI bacterial colonization, translocation, and toxin absorption.
Safety & warnings
Contraindications
- Known hypersensitivity to oseltamivir
- Poultry (chickens, turkeys, ducks) - FDA banned for extra-label use
Adverse effects
- Gastrointestinal upset (nausea, vomiting - usually transient)
- Insomnia (reported in humans)
- Vertigo (reported in humans)
Precautions
Public Health & Ethical Considerations: Routine use in dogs and cats is discouraged to prevent viral resistance and preserve human stockpiles for pandemic influenza.
- Timing: For true influenza infections, treatment must begin as early as possible (ideally within 40-48 hours of clinical signs onset) to be effective.
- Renal Impairment: Dosages may need adjustment in patients with severe renal insufficiency, as the active metabolite is primarily renally excreted.
- Neonatal Toxicity: High doses in neonatal rats showed significant accumulation in the brain compared to adults. Use with extreme caution in newborn puppies or kittens due to potential neurotoxicity.
- Pregnancy: FDA Category C. Minor skeletal abnormalities noted in high-dose rabbit studies. Use only if benefits outweigh risks.
Drug interactions
May increase 2-fold the exposure to oseltamivir carboxylate (active metabolite) by reducing renal tubular secretion.
May potentially reduce the immune response to live influenza virus vaccines. No effect on inactivated (killed) vaccines.
Monitoring
- Clinical efficacy (resolution of clinical signs, weight gain, WBC count maintenance in parvo)
- Gastrointestinal tolerance
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed after oral administration. In humans, bioavailability of the active carboxylate form is about 75%.
Distribution
Minimally bound to plasma proteins.
Metabolism
Prodrug is converted into the active oseltamivir carboxylate predominantly via liver esterases. Does not act as a substrate or inhibitor for CYP-450 isoenzymes.
Elimination
Primarily eliminated via renal mechanisms (both glomerular filtration and tubular secretion). Up to 20% of a dose may be eliminated in the feces.
Overdose
Oseltamivir has a relatively low toxic potential. In humans, massive overdoses (up to 1000 mg) have primarily caused only gastrointestinal signs such as nausea and vomiting. Treatment should be supportive and symptomatic.
Available products
Formulations
- Oral capsules
- Powder for oral suspension
Human-labeled
- Oseltamivir Phosphate Oral Capsules: 30 mg, 45 mg, & 75 mg (as base); Tamiflu®
- Oseltamivir Phosphate Powder for Oral Suspension: 12 mg/mL (as base) after reconstitution; Tamiflu®
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Capsules should be stored at 25°C (15-30°C permitted). Oral powder should be stored between 15-30°C. Once reconstituted with water, the suspension should be stored at room temperature (15-30°C) or in the refrigerator (2-8°C) and protected from freezing. Reconstituted suspension is stable for 10 days.
Client information
- Experimental Use: If prescribed for your pet (such as for parvovirus), understand that this is an experimental, "off-label" use of a human medication.
- Administration: It is crucial to give this medication exactly as prescribed. If your pet is vomiting, your veterinarian may recommend giving an anti-nausea injection about 30 minutes before giving this oral medication to help them keep it down.
- Side Effects: The most common side effect is mild stomach upset (nausea or vomiting). Giving the medication with a small amount of food may help reduce this.
- Public Health: This drug is the same as human Tamiflu®. Its use in pets is controversial because it is an important drug for human flu pandemics.
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.