Ondansetron
Ondansetron hydrochloride dihydrate
Also known as: Zofran · Setofilm · GR-38032F · ondansetroni hydrochloridum · Ondansetronum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceVomiting associated with chronic kidney disease (extra-label) — IRIS Stage 3
Verified clinician required
- q6-12h
NA
Governing clinical context (4)
- NOTE: In humans, it is recommended that IV administration of ondansetron occur over at least 30 seconds, and preferably over 2 to 5 minutes. 24
- Vomiting associated with chronic kidney disease (extra-label):
- Unless otherwise labeled, store oral products in tight, light-resistant containers between 20°C and 25°C (68°F-77°F); temperature excursions of 15°C to 30°C (59°F-86°F) are permitted for the oral solution. Store orally disintegrating tablets in the original foil blisters and administer immediately upon opening; discard opened/unused tablets or tablet remnants. Store the injection between 2°C and 25°C (36°F-77°F) and protected from light. Solutions diluted for IV infusion retain potency for 48 hours at room temperature, but the manufacturer recommends discarding them 24 hours after dilution.
- ■ This medicine is used to treat or prevent severe vomiting. The oral medication may be given with or without food.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Ondansetron is a highly effective, centrally and peripherally acting antiemetic belonging to the 5-HT3 receptor antagonist class.
Key clinical highlights:
- Refractory Vomiting: Often utilized as a rescue or second-line antiemetic when conventional therapies (like maropitant or metoclopramide) are insufficient.
- Chemotherapy & Severe Disease: Considered a gold standard for preventing and treating chemotherapy-induced nausea and vomiting (CINV), particularly with highly emetogenic drugs like cisplatin. It is also widely used in severe cases of parvoviral enteritis, pancreatitis, and uremia.
- Species Considerations: Generally well-tolerated in dogs. Its use in cats has historically been debated, but it is frequently used in feline practice for intractable vomiting and severe pancreatitis with good clinical success.
Clinical Pearl: Ondansetron does not possess prokinetic properties. If gastric stasis or ileus is present, it will not resolve the motility issue and may mask underlying gastric distention.
Mechanism of action
Ondansetron is a highly selective and competitive 5-HT3 (serotonin type 3) receptor antagonist.
- Peripheral Action: Cytotoxic drugs, severe inflammation (e.g., pancreatitis), or viral infections (e.g., parvovirus) cause cellular damage in the GI tract, triggering the release of serotonin from enterochromaffin cells. This serotonin binds to 5-HT3 receptors on vagal afferent nerve terminals, sending emetogenic signals to the brain. Ondansetron blocks these peripheral receptors.
- Central Action: It also directly antagonizes 5-HT3 receptors located in the Chemoreceptor Trigger Zone (CTZ) within the area postrema of the brainstem, preventing central emetic signaling to the vomiting center.
- Net Effect: Profound inhibition of the vomiting reflex without altering GI motility or causing significant sedation.
Safety & warnings
Contraindications
- Hypersensitivity to ondansetron or other 5-HT3 antagonists
- Concurrent use with apomorphine (due to risk of severe hypotension)
- Intestinal obstruction
Adverse effects
- Constipation
- Sedation
- Extrapyramidal clinical signs (head shaking)
- Arrhythmias
- Hypotension
- Headaches (reported in humans)
- Alterations in liver enzymes
- Hypersensitivity reactions (rare)
Precautions
Ondansetron may mask ileus or gastric distention; it should not be used in place of nasogastric suction. Use with caution in patients with hepatic dysfunction as the half-life may be prolonged. Caution is advised when administering to dogs with the MDR1/ABCB1 mutation, as it is a known P-glycoprotein substrate in humans. Exercise caution in nursing patients as it is excreted in maternal milk.
Drug interactions
Severe hypotension reported in humans; concurrent use is contraindicated.
Theoretically may have additive effects on QTc interval, potentially resulting in serious arrhythmias.
May reduce the efficacy of both drugs (human data); veterinary significance is unknown.
Monitoring
- Clinical efficacy (reduction or cessation of vomiting)
- Hydration status and electrolyte balance (due to underlying vomiting)
- Resolution of nausea and vomiting
- Liver enzymes (with prolonged use)
- Bowel movements (monitor for constipation)
Pharmacokinetics
Half-life
Absorption
In humans, well absorbed from the GI tract but exhibits first-pass hepatic metabolism. Bioavailability is about 50-60%. Peak plasma levels occur about 2 hours after an oral dose.
Distribution
No veterinary species data located.
Metabolism
Extensively metabolized in the liver.
Elimination
Elimination half-lives in humans are about 3-4 hours, prolonged in elderly patients or those with hepatic dysfunction.
Overdose
Overdoses of up to 10X did not cause significant morbidity in human subjects. If an overdose occurs, treat supportively.
Available products
Formulations
- Orally disintegrating tablets (ODT)
- Oral solution
- Injection
- Injectable: 2 mg/ml solution in 2 ml and 4 ml ampoules
- Oral: 4 mg, 8 mg tablets
- Oral: 4 mg/5 ml syrup
- Rectal: 16 mg suppositories
Human-labeled
- Ondansetron HCl Tablets: 4 mg, 8 mg, 16 mg & 24 mg
- Ondansetron Orally Disintegrating Tablets: 4 mg & 8 mg
- Ondansetron HCl Oral Solution: 0.8 mg/ml (4 mg/5 mL)
- Ondansetron HCl Injection: 2 mg/mL in 2 mL & 20 mL vials; 32 mg/50 mL premixed
- Setofilm
- Zofran (2 mg/ml injectable, 4 mg and 8 mg tablets, 4 mg/5 ml syrup, 16 mg suppositories)
Regulatory status
POM (Prescription Only Medicine)
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unless otherwise labeled, store oral products in tight, light-resistant containers between 2-30°C. The injection should be stored between 2-30°C and protected from light.
Client information
Ondansetron is a potent anti-nausea medication often used when other common medications have failed, or for severe conditions like parvovirus, pancreatitis, or during chemotherapy.
- Administration: Can be given with or without food. If your pet vomits shortly after taking the pill, contact your veterinarian before giving another dose.
- Orally Disintegrating Tablets (ODT): If you are prescribed the "melting" tablets, handle them with dry hands. Do not push the tablet through the foil backing; instead, peel the foil back to remove the tablet. Place it gently in your pet's mouth where it will dissolve quickly.
- Side Effects: Generally very well tolerated. Mild sleepiness or constipation can occasionally occur. Contact your vet if you notice unusual head shaking or extreme lethargy.
- Storage: Keep out of reach of children and other pets. Store at room temperature away from light and moisture.
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.