# Ondansetron: veterinary dose and monograph

> Ondansetron is a veterinary antiemetic. 5-HT3 receptor antagonist — a central and peripheral antiemetic. Indications include refractory vomiting (parvovirus, pancreatitis, CKD); chemotherapy-induced nausea / vomiting; adjunct to maropitant for breakthrough vomiting. This monograph lists 4 reference doses for dogs, cats and primates, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/ondansetron · Last reviewed: 2026-10-01

## 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

*Ondansetron doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Antiemetic (general) | 0.1–0.5 mg/kg | IV | q6–12h (slow IV) | — |
| Chemotherapy-induced vomiting | 0.5–1 mg/kg | IV | 30 min before chemotherapy | — |

- 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

*Ondansetron doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Refractory vomiting / CKD nausea | 0.1–0.5 mg/kg | IV | q8–12h | — |

- 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

*Ondansetron doses for primates*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Antiemetic (monkeys, macaques) | 0.1–1 mg/kg | IV | q24h | — |

- 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

> **Caution:** 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](https://vetmasterji.com/drugs/dolasetron)
- [Maropitant](https://vetmasterji.com/drugs/maropitant)

## Frequently asked questions

### What is the dose of Ondansetron for dogs?

Reference doses for Ondansetron in dogs: 0.1–0.5 mg/kg IV q6–12h (slow IV) (Antiemetic (general)); 0.5–1 mg/kg IV 30 min before chemotherapy (Chemotherapy-induced vomiting). Confirm against the label and the patient before use.

### What is the dose of Ondansetron for cats?

Reference doses for Ondansetron in cats: 0.1–0.5 mg/kg IV q8–12h (Refractory vomiting / CKD nausea). Confirm against the label and the patient before use.

### What is the dose of Ondansetron for primates?

Reference doses for Ondansetron in primates: 0.1–1 mg/kg IV q24h (Antiemetic (monkeys, macaques)). Confirm against the label and the patient before use.

### When should Ondansetron not be used?

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

### What are the side effects of Ondansetron in animals?

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

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition
- Carpenter, Exotic Animal Formulary

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.