Zofran for Dogs Dosage Calculator
Precise ondansetron (Zofran) dosing for dogs by weight, route of administration, and indication — with tablet and IV formulation breakdowns.
Veterinary guidance required. Ondansetron should be used under veterinary supervision. QT prolongation risk at high doses. Always confirm diagnosis before antiemetic therapy.
About Ondansetron (Zofran)
Drug Class
Serotonin 5-HT₃ Receptor Antagonist — Antiemetic
Mechanism of Action
Ondansetron selectively blocks serotonin 5-HT₃ receptors in the GI tract and CNS, preventing nausea signals from reaching the vomiting centre in the brain. It does not affect dopamine receptors (unlike metoclopramide), so it lacks prokinetic activity.
Primary Uses in Dogs
Nausea and vomiting from chemotherapy, parvovirus, pancreatitis, kidney disease (uraemic nausea), and post-operative nausea. Particularly useful when vomiting is refractory to other antiemetics.
Dosing Quick Reference
| Indication | Dose | Frequency |
|---|---|---|
| Antiemetic | 0.1–1 mg/kg | q8–12h PO/IV |
| Chemotherapy nausea | 0.5–1 mg/kg | 30 min pre-chemo IV |
| Severe vomiting | 0.1–0.2 mg/kg | IV slow bolus |
Common Side Effects
- Constipation (most common)
- Mild sedation
- Elevated liver enzymes (rare, long-term)
- QT interval prolongation at very high doses
- Serotonin syndrome risk if combined with SSRIs/MAOIs
Monitoring
Monitor liver enzymes with long-term use. If vomiting persists despite ondansetron, reassess diagnosis.
What Is Ondansetron (Zofran)?
Ondansetron is a selective 5-HT₃ serotonin receptor antagonist widely used in veterinary medicine to control nausea and vomiting in dogs. It acts centrally at the chemoreceptor trigger zone (CTZ) and peripherally in the GI tract, making it effective for chemotherapy-induced emesis, parvovirus, pancreatitis, vestibular disease, and post-operative nausea.
Unlike metoclopramide, ondansetron does not cross the blood-brain barrier significantly and has minimal dopamine receptor activity, making it better tolerated with fewer CNS side effects. It is available as tablets (4 mg, 8 mg), orally disintegrating tablets (ODT), and injectable solution (2 mg/mL).
Clinical Pharmacology
- Mechanism: Selective 5-HT₃ antagonist at CTZ and gut vagal afferents
- Onset (IV): ~30 minutes; oral bioavailability ~60% in dogs
- Half-life: 1.5–3 hours in dogs (shorter than in humans)
- Metabolism: Hepatic CYP3A4; dose-reduce in liver disease
- Available forms: 4 mg, 8 mg tablets; 4 mg, 8 mg ODT; 2 mg/mL injectable
How to Use This Calculator
- Enter your dog’s body weight in kg or lbs
- Select the route of administration (oral or IV)
- Select the clinical indication
- Choose your available tablet/vial strength
- Press Calculate to see dose, frequency, and tablet count
🧮 Ondansetron Dose Calculator
Ondansetron Dosing Result
Dosing Reference Table
| Indication | Route | Dose | Frequency |
|---|---|---|---|
| General nausea | Oral | 0.5–1 mg/kg | q8–12h |
| Chemotherapy | Oral / IV | 0.5–1 mg/kg | q8h |
| IV standard | Intravenous | 0.1–0.5 mg/kg | q6–12h |
Important Safety Information
- Do not use in dogs with known hypersensitivity to serotonin antagonists
- QT interval prolongation possible — use with caution in cardiac patients
- Reduce dose in dogs with hepatic insufficiency
- Drug interactions: avoid co-administration with other serotonergic drugs (tramadol, SSRIs) due to serotonin syndrome risk
- Ondansetron masks vomiting but does not treat the underlying cause — always investigate the primary condition
References
- Plumb DC. Plumb’s Veterinary Drug Handbook, 9th ed. Wiley-Blackwell; 2018.
- Trepanier LA. Acute vomiting in cats: rational treatment selection. J Feline Med Surg. 2010;12(3):225-230.
- Marks SL, et al. ACVIM consensus statement: support for rational administration of gastrointestinal protectants to dogs and cats. J Vet Intern Med. 2018;32(6):1823-1840.
- Hansen BD. Analgesia for the critically ill dog or cat. Vet Clin North Am Small Anim Pract. 2000;30(5):1127-1155.