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PetDosageChart

Zofran (Ondansetron) Dosage for Dogs

Serotonin (5-HT3) receptor antagonist antiemetic ⏱ Onset: 30 minutes (oral) ⏳ Duration: 8-12 hours

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator

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Zofran Dosage Chart for Dogs by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
5 lbs (2.3 kg) 1mg 1.5mg 2.5mg Every 8-12 hours
10 lbs (4.5 kg) 2.5mg 3.5mg (4mg tablet) 4.5mg (4mg tablet) Every 8-12 hours
15 lbs (6.8 kg) 3.5mg (4mg tablet) 5mg 7mg (2 × 4mg) Every 8-12 hours
20 lbs (9.1 kg) 4.5mg (4mg tablet) 7mg (2 × 4mg) 9mg Every 8-12 hours
25 lbs (11.3 kg) 5.5mg 8.5mg (2 × 4mg) 11.5mg (3 × 4mg) Every 8-12 hours
30 lbs (13.6 kg) 7mg (2 × 4mg) 10mg 13.5mg Every 8-12 hours
40 lbs (18.1 kg) 9mg 13.5mg 18mg Every 8-12 hours
50 lbs (22.7 kg) 11.5mg (3 × 4mg) 17mg 22.5mg Every 8-12 hours
60 lbs (27.2 kg) 13.5mg 20.5mg (5 × 4mg) 27mg (7 × 4mg) Every 8-12 hours
70 lbs (31.7 kg) 16mg (4 × 4mg) 24mg (6 × 4mg) 31.5mg (8 × 4mg) Every 8-12 hours
80 lbs (36.3 kg) 18mg 27mg (7 × 4mg) 36.5mg (9 × 4mg) Every 8-12 hours
90 lbs (40.8 kg) 20.5mg (5 × 4mg) 30.5mg 41mg Every 8-12 hours
100 lbs (45.4 kg) 22.5mg 34mg 45.5mg Every 8-12 hours
120 lbs (54.4 kg) 27mg (7 × 4mg) 41mg 54.5mg Every 8-12 hours
150 lbs (68 kg) 34mg 51mg (13 × 4mg) 68mg (17 × 4mg) Every 8-12 hours

What is Zofran (Ondansetron) used for in dogs?

Nausea and vomiting Chemotherapy-induced nausea Post-operative nausea Parvovirus-associated vomiting Motion sickness

How to give Zofran to your dog

Give ondansetron tablets by mouth 30 minutes before meals or triggers (such as chemotherapy). The orally disintegrating tablet (ODT) can be placed directly on the tongue where it dissolves without water, which is especially useful for a vomiting dog. Regular tablets can be given with a small amount of food if tolerated. Administer every 8-12 hours as directed.

Available Forms

Tablet, Orally disintegrating tablet, Injectable

Give with Food?

No — can be given without food

Side effects of Zofran in dogs

Common side effects

Mild sedation
Constipation
Headache (presumed)
Diarrhea

Serious side effects

  • QT prolongation (heart rhythm changes)
  • Serotonin syndrome when combined with serotonergic drugs
  • Severe constipation or ileus
  • Hypersensitivity reaction

When to call the vet

Call your vet immediately if your dog shows any of these signs:

  • Vomiting persists despite ondansetron treatment
  • Blood in vomit or stool
  • Signs of dehydration (dry gums, skin tenting, sunken eyes)
  • Severe lethargy or inability to keep any water down
  • Tremors or signs of serotonin syndrome (agitation, rapid heart rate, high temperature)

Related Medications for Dogs

NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart
GI prokinetic / Antiemetic (dopamine antagonist)

Reglan

Metoclopramide

For Nausea and vomiting

View dosage chart
Serotonin antagonist and reuptake inhibitor (SARI)

Desyrel

Trazodone

For anxiety

View dosage chart
H2 receptor antagonist

Pepcid

Famotidine

For stomach acid reduction

View dosage chart

Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Ondansetron.

Frequently Asked Questions

Is ondansetron safe for dogs?
Yes, ondansetron is considered safe and effective for dogs when used at appropriate doses under veterinary guidance. It is widely used in veterinary emergency and oncology settings. The most common side effects are mild sedation and constipation.
Can I give my dog human Zofran?
Many veterinarians prescribe human ondansetron (Zofran) for dogs at appropriate veterinary doses. The orally disintegrating tablet (ODT) form can be especially useful for vomiting dogs as it dissolves on the tongue. Always get proper dosing from your veterinarian.
How quickly does ondansetron stop vomiting in dogs?
Oral ondansetron typically begins working within 30 minutes. The injectable form works within minutes. It is one of the most effective antiemetics available and works by blocking serotonin receptors in the vomiting center of the brain and in the GI tract.
Can ondansetron be used for dogs with parvovirus?
Yes, ondansetron is commonly used in the management of parvovirus to control severe vomiting. In hospitalized parvo puppies, the injectable form is typically used initially since oral medications may not stay down. Once vomiting is controlled, oral dosing can continue.
What is the difference between ondansetron and Cerenia for dogs?
Both are antiemetics but work through different mechanisms. Cerenia (maropitant) blocks NK1 receptors and is FDA-approved for dogs, while ondansetron blocks 5-HT3 serotonin receptors and is used off-label. Both are effective; sometimes they are used together for severe nausea. Cerenia also has anti-nausea effects beyond just anti-vomiting.

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