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PetDosageChart

Serotonin (5-HT3) receptor antagonist antiemetic · For Dogs

How much Zofran (Ondansetron) can I give my dog?

Standard Zofran dose for dogs is 0.75 mg per kg (0.34 mg per lb), given Every 8-12 hours. Use the calculator below for your dog's exact weight, or jump to the weight-by-weight chart.

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

Calculator estimate from Plumb’s Veterinary Drug Handbook. Not yet vet-reviewed — see our methodology .

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. Sourced from Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator · 01

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By Weight

Zofran dose by dog weight

Pick your dog's weight to jump to a dedicated page with the dose, frequency, safety notes, and FAQ for that size.

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Dosage Chart · 02

Zofran dosage for dogs by weight

Scroll sideways to see full table

Weight Low Dose Standard Max Safe 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

Common Uses · 03

What is Zofran (Ondansetron) used for in dogs?

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

Administration · 04

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 · 05

Side effects of Zofran in dogs

Common side effects

Mild sedation
Constipation
Headache (presumed)
Diarrhea

Serious side effects — call your vet

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

Emergency · 06

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)

For Cats

Looking for Zofran dosage for cats?

View the Zofran dosage chart and calculator for cats.

Related · 08

Related medications for dogs

Sources · 09

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.

Read more about our methodology and how we calculate dosages.

Transparency · 11

How this page was made

Sourced from Plumb's Veterinary Drug Handbook, the reference used in US vet schools. Every dose, frequency, and tablet count on this page is generated from that data, then checked against the published references below.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 0.75 mg per kg (0.34 mg per lb) of body weight, given Every 8-12 hours. The calculator multiplies that basis by your dog's weight and rounds to the closest available tablet size.
Last-reviewed status
Automated from Plumb’s, not yet vet-reviewed.

More on our methodology and editorial process — how we source, calculate, and review dogs dosage data.

Frequently Asked · 07

Questions about this medication

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.

Safety · 10

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