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

Zofran dosage reference for dogs (Ondansetron)

This page's standard weight-based reference is 0.75 mg per kg (0.34 mg per lb), with Every 8-12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your dog's weight, then confirm the indication, product, and actual dose with a veterinarian.

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

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Ondansetron (often known by brand names such as Zofran) is a serotonin (5-HT3) receptor antagonist antiemetic commonly used in veterinary medicine for Nausea and vomiting, Chemotherapy-induced nausea, Post-operative nausea, Parvovirus-associated vomiting, and Motion sickness. Understanding the correct dosage, administration, and potential side effects of Ondansetron is critical for your dog’s safety and well-being.

A typical Ondansetron dose for dogs is around 0.75 mg/kg Every 8-12 hours, within a usual range of 0.5-1 mg/kg. Available forms include Tablet, Orally disintegrating tablet, and Injectable.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Ondansetron Dosage Calculator for Dogs

Enter your dog’s weight below to estimate the Ondansetron dose from the 0.75 mg/kg guideline. Your veterinarian may adjust it for your dog’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your dog's weight

Quick Dosage Chart

Typical Ondansetron amounts for common dog weights, for quick reference:

Dosage Chart · 02

Zofran weight-based reference chart for dogs

Scroll sideways to see full table

Weight	Lower Reference	Standard Reference	Upper Reference	Frequency
5 lbs (2.3 kg)	1.1 mg	1.7 mg	2.3 mg	Every 8-12 hours
10 lbs (4.5 kg)	2.3 mg	3.4 mg (4mg tablet)	4.5 mg (4mg tablet)	Every 8-12 hours
15 lbs (6.8 kg)	3.4 mg (4mg tablet)	5.1 mg	6.8 mg	Every 8-12 hours
20 lbs (9.1 kg)	4.5 mg (4mg tablet)	6.8 mg	9.1 mg	Every 8-12 hours
25 lbs (11.3 kg)	5.7 mg	8.5 mg (2 × 4mg)	11.3 mg (3 × 4mg)	Every 8-12 hours
30 lbs (13.6 kg)	6.8 mg	10.2 mg	13.6 mg	Every 8-12 hours
40 lbs (18.1 kg)	9.1 mg	13.6 mg	18.1 mg	Every 8-12 hours
50 lbs (22.7 kg)	11.3 mg (3 × 4mg)	17.0 mg	22.7 mg	Every 8-12 hours
60 lbs (27.2 kg)	13.6 mg	20.4 mg (5 × 4mg)	27.2 mg (7 × 4mg)	Every 8-12 hours
70 lbs (31.7 kg)	15.8 mg (4 × 4mg)	23.8 mg (6 × 4mg)	31.7 mg (8 × 4mg)	Every 8-12 hours
80 lbs (36.3 kg)	18.1 mg	27.2 mg (7 × 4mg)	36.3 mg (9 × 4mg)	Every 8-12 hours
90 lbs (40.8 kg)	20.4 mg (5 × 4mg)	30.6 mg	40.8 mg (10 × 4mg)	Every 8-12 hours
100 lbs (45.4 kg)	22.7 mg	34.0 mg	45.4 mg	Every 8-12 hours
120 lbs (54.4 kg)	27.2 mg (7 × 4mg)	40.8 mg (10 × 4mg)	54.4 mg	Every 8-12 hours
150 lbs (68 kg)	34.0 mg	51.0 mg (13 × 4mg)	68.0 mg (17 × 4mg)	Every 8-12 hours

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Zofran reference by dog weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Ondansetron 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.

It may interact with Apomorphine — ondansetron blocks its emetic action (do not use together), Tramadol and other serotonergic drugs — increased serotonin syndrome risk, SSRIs (fluoxetine) — additive serotonin effects, and Cisapride — potential QT prolongation.

Side Effects and Safety

Common side effects include Mild sedation, Constipation, Headache (presumed), and Diarrhea. More serious side effects can occur, such as QT prolongation (heart rhythm changes), Serotonin syndrome when combined with serotonergic drugs, Severe constipation or ileus, and Hypersensitivity reaction.

Cautions · 12

When Zofran should be used with caution or avoided

Some dogs should not take Zofran, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Zofran.

Known hypersensitivity to ondansetron
Concurrent use with apomorphine (blocks its emetic effect)
Severe hepatic impairment (dose adjustment needed)

Interactions · 13

Zofran drug interactions

Zofran can interact with other drugs. This list is not complete — always give your veterinarian a full list of your dog's medications and supplements.

Apomorphine — ondansetron blocks its emetic action (do not use together)

Tramadol and other serotonergic drugs — increased serotonin syndrome risk

SSRIs (fluoxetine) — additive serotonin effects

Cisapride — potential QT prolongation

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult dog at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

In an emergency, or after accidental ingestion or a suspected overdose
For pregnant or nursing pets
For very young or very old dogs
For pets with liver disease, kidney disease, or another chronic illness
For pets taking several medications at once
When you are not sure of your dog's current, accurate weight
For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your dog had too much Zofran, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

Call your veterinarian or the nearest emergency animal hospital.
ASPCA Animal Poison Control Center: (888) 426-4435
Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your dog experiences any of the following, contact your veterinarian or an emergency clinic immediately:

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)

Frequently Asked Questions

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.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your dog's weight by the lower, standard, and upper mg/kg values recorded for Zofran. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses: Nausea and vomiting, Chemotherapy-induced nausea, Post-operative nausea, Parvovirus-associated vomiting, Motion sickness
Recorded forms: Tablet, Orally disintegrating tablet, Injectable
Reference timing: Every 8-12 hours; onset 30 minutes (oral); duration 8-12 hours

Individual checks a calculator cannot perform

Confirm the diagnosis and the reason this medication is being considered.
Match the exact product, concentration, route, and whether a tablet may be split.
Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

Known hypersensitivity to ondansetron; Concurrent use with apomorphine (blocks its emetic effect); Severe hepatic impairment (dose adjustment needed).

Recorded interactions

Apomorphine — ondansetron blocks its emetic action (do not use together); Tramadol and other serotonergic drugs — increased serotonin syndrome risk; SSRIs (fluoxetine) — additive serotonin effects; Cisapride — potential QT prolongation.

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your dog's complete medication list before acting on a number.

Related · 08

Related medications for dogs

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Plumb's Veterinary Drug Handbook — listed in this medication's source record.
Merck Veterinary Manual — listed in this medication's source record.
DailyMed label search for Ondansetron — check current product and formulation labels; some veterinary uses may be off-label.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

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 shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner: Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status: Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

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

Safety · 10

More resources

Pet Medication Safety Hub — What's safe, what's dangerous, and emergency signs
How we calculate dosages — Our sources, math, and review process
Printable emergency checklist — One-page reference for your fridge or first aid kit