Ondansetron: veterinary dose and monograph

At a glance

Drug class

Antiemetic

Also known as

Zofran, Emeset

Species with doses

Dogs, Cats and Primates

General dose range

0.1–1 mg/kg IV q8–12h — check the species tables for the indication

Routes

IV

Last reviewed

1 October 2026

Indications

• Refractory vomiting (parvovirus, pancreatitis, CKD)
• Chemotherapy-induced nausea / vomiting
• Adjunct to maropitant for breakthrough vomiting

Ondansetron dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Antiemetic (general): Papich 5e: vomiting from other causes 0.1–0.2 mg/kg slow IV q6–12h, increasing to 0.5 mg/kg if ineffective. Plumb’s p.909: 0.1–0.3 mg/kg slow IV q8–12h — dramatic results in parvovirus and pancreatitis (Tams 2007); 0.1–0.2 mg/kg IV q6–12h (Otto 2005); uraemia 0.6–1 mg/kg PO or IV q12h.
• Chemotherapy-induced vomiting: Papich 5e: 0.5–1 mg/kg IV or SC 30 min before IV cancer drugs. Plumb’s p.909 (Kent 2009): 0.1–0.5 mg/kg IV over 15 min q8h, or 0.5–1 mg/kg PO q8–12h. Oral bioavailability in dogs is under 10% (Papich).

Cats

• Refractory vomiting / CKD nausea: Papich 5e: 0.5 mg/kg q8h SC, IV or PO (2 mg per cat — half a tablet — q8h is common); reduce to q12h with liver disease; CRI 0.5 mg/kg IV then 0.5 mg/kg/h. Plumb’s p.909: 0.5 mg/kg IV or PO twice daily (Trepanier 2010); intractable vomiting 0.1–0.15 mg/kg slow IV q6–12h (Scherk 2003).

Primates

• Antiemetic (monkeys, macaques): Carpenter Exotic Animal Formulary 6th ed, Table 13-7 (p.710): monkeys 0.1 mg/kg slow IV q24h or 1 mg/kg SC q24h; macaques 4 mg/animal PO prophylaxis 30 min before. Sedation is a common side effect.

Contraindications

Known hypersensitivity. Use cautiously with other QT-prolonging drugs; reduce the dose in significant hepatic impairment.

Adverse effects

• Generally well tolerated
• Constipation, sedation (occasional)
• Rare QT prolongation at high IV doses

Drug interactions

• Apomorphine: a human patient given both developed SEVERE HYPOTENSION - the combination is contraindicated in humans. Relevant in small-animal practice, where apomorphine is the standard emetic
• Drugs affecting the QTc interval (amiodarone, cisapride, halothane, isoflurane, sotalol): theoretically additive QTc effects with possible serious arrhythmias
• Tramadol: in humans the combination may reduce the efficacy of BOTH drugs; veterinary significance unknown

Toxicity and overdose

Plumb's p.909: overdoses of up to 10x did not cause significant morbidity in human subjects; treat supportively if one occurs. The wide margin means the practical risks are the interactions rather than the dose - chiefly additive QTc prolongation with inhalational anaesthetics, and the masking of ileus or gastric distention noted under precautions.

Clinical pearls

• Layer with maropitant (different mechanism) for parvo / pancreatitis vomiting that breaks through single-agent therapy
• Plumb's p.909 flags an important blind spot: ondansetron may MASK ileus or gastric distention — it is not a substitute for nasogastric suction, so keep decompressing and imaging the vomiting patient
• Give slow IV — a rapid push can cause transient dysrhythmia
• Treats vomiting but not the cause — always pursue and address the primary disease

Mechanism of action

Plumb's p.909: 5-HT3 (serotonin type 3) receptor ANTAGONIST. 5-HT3 receptors sit peripherally on vagal nerve terminals and centrally in the chemoreceptor trigger zone (CTZ); Plumb's notes it is not clear whether ondansetron acts centrally, peripherally or both. This dual siting is why it works for chemotherapy- and toxin-driven vomiting that antihistaminic or dopaminergic antiemetics miss. No veterinary pharmacokinetic data was located; in humans it is well absorbed orally with some first-pass metabolism (bioavailability 50-60%), peak levels at about 2 hours, extensive hepatic metabolism and a 3-4 hour elimination half-life.

Formulations and products

• Ondansetron 2 mg/mL injection
• Ondansetron 4 mg tablet
• Ondansetron 8 mg tablet

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antiemetics

• Dolasetron
• Maropitant

Frequently asked questions