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Serotonin (5-HT3) antagonist antiemetic · For Cats

Zofran dosage reference for cats (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 cat's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset
30-60 minutes (oral), 10-15 minutes (injectable)
Duration
8-12 hours
Class
Serotonin (5-HT3) 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) antagonist antiemetic commonly used in veterinary medicine for nausea, vomiting, chemotherapy-induced nausea, post-anesthetic nausea, and motion sickness. Understanding the correct dosage, administration, and potential side effects of Ondansetron is critical for your cat’s safety and well-being.

A typical Ondansetron dose for cats is around 0.75 mg/kg every 8-12 hours, within a usual range of 0.5-1 mg/kg. Available forms include tablet, injectable, and oral dissolving tablet.

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 Cats

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

Dosage Calculator · 01

Enter your cat's weight

Quick Dosage Chart

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

Dosage Chart · 02

Zofran weight-based reference chart for cats

Scroll sideways to see full table

Weight Lower Reference Standard Reference Upper Reference Frequency
3 lbs (1.4 kg) 0.70 mg 1.0 mg 1.4 mg every 8-12 hours
4 lbs (1.8 kg) 0.90 mg 1.4 mg 1.8 mg every 8-12 hours
5 lbs (2.3 kg) 1.1 mg 1.7 mg 2.3 mg every 8-12 hours
6 lbs (2.7 kg) 1.4 mg 2.0 mg 2.7 mg every 8-12 hours
7 lbs (3.2 kg) 1.6 mg 2.4 mg 3.2 mg (4mg tablet) every 8-12 hours
8 lbs (3.6 kg) 1.8 mg 2.7 mg 3.6 mg (4mg tablet) every 8-12 hours
9 lbs (4.1 kg) 2.0 mg 3.1 mg (4mg tablet) 4.1 mg (4mg tablet) 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
12 lbs (5.4 kg) 2.7 mg 4.1 mg (4mg tablet) 5.4 mg every 8-12 hours
14 lbs (6.3 kg) 3.1 mg (4mg tablet) 4.7 mg (4mg tablet) 6.3 mg every 8-12 hours
16 lbs (7.3 kg) 3.6 mg (4mg tablet) 5.5 mg 7.3 mg (2 × 4mg) every 8-12 hours
18 lbs (8.2 kg) 4.1 mg (4mg tablet) 6.1 mg 8.2 mg (2 × 4mg) 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

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 cat 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 Cat

Ondansetron can be given with or without food. For cats, a typical dose is 0.5-1 mg/kg, which usually means a quarter to half of a 4 mg tablet for an average cat. The oral dissolving tablet (ODT) can be placed on the tongue where it dissolves quickly — this is helpful for cats that are actively nauseous and may vomit up a regular tablet. For severe vomiting, the injectable form can be given by your vet to bypass the GI tract entirely.

It may interact with SSRIs (serotonin syndrome risk), tramadol, other QT-prolonging drugs, and apomorphine (reduced efficacy).

Side Effects and Safety

Common side effects include constipation, mild sedation, headache, and mild diarrhea. More serious side effects can occur, such as cardiac arrhythmias (QT prolongation), serotonin syndrome with other serotonergic drugs, severe constipation, and hypersensitivity reaction.

Cautions · 12

When Zofran should be used with caution or avoided

Some cats 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 cardiac conduction abnormalities
  • concurrent use with other QT-prolonging drugs
  • known hypersensitivity
  • pregnancy

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 cat's medications and supplements.

SSRIs (serotonin syndrome risk)
tramadol
other QT-prolonging drugs
apomorphine (reduced efficacy)

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult cat 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 cats
  • 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 cat's current, accurate weight
  • For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

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

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

Is ondansetron safe for cats?
Yes, ondansetron is considered safe and effective for cats. It is one of the most potent antiemetics available and is widely used in both human and veterinary medicine. It works by blocking serotonin receptors in the vomiting center of the brain and in the GI tract. It has fewer sedating effects than some other antiemetics.
How is ondansetron different from Cerenia for cats?
Both are effective antiemetics but work through different mechanisms. Cerenia (maraviroc) blocks substance P, while ondansetron blocks serotonin (5-HT3) receptors. Cerenia is FDA-approved for dogs but used off-label in cats. Ondansetron may be preferred for chemotherapy-induced nausea and is available in more convenient forms like oral dissolving tablets.
Can I give my cat ondansetron for car sickness?
Yes, ondansetron can help with motion sickness in cats. Give it 30-60 minutes before travel. However, for routine travel nausea, Cerenia (maropitant) may be more effective as it specifically targets motion-induced vomiting pathways. Consult your vet about the best option for your cat.
How much ondansetron can I give my cat?
The typical dose is 0.5-1 mg/kg every 8-12 hours. For an average 4-5 kg cat, this means approximately 2-4 mg per dose. A quarter to half of a 4 mg tablet is a common starting dose. Always follow your veterinarian's specific dosing instructions.
Can ondansetron be used with other medications?
Ondansetron can be safely combined with most medications, but caution is needed with serotonergic drugs (SSRIs like fluoxetine, tramadol) due to serotonin syndrome risk, and with drugs that prolong the QT interval on ECG. Always inform your vet of all medications your cat is taking.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your cat'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, vomiting, chemotherapy-induced nausea, post-anesthetic nausea, motion sickness
Recorded forms
tablet, injectable, oral dissolving tablet
Reference timing
every 8-12 hours; onset 30-60 minutes (oral), 10-15 minutes (injectable); 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 cardiac conduction abnormalities; concurrent use with other QT-prolonging drugs; known hypersensitivity; pregnancy.

Recorded interactions

SSRIs (serotonin syndrome risk); tramadol; other QT-prolonging drugs; apomorphine (reduced efficacy).

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

For Dogs

Looking for Zofran dosage for dogs?

View the Zofran dosage chart and calculator for dogs.

Related · 08

Related medications for cats

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.

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 cat'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 cats dosage data.

Safety · 10

More resources