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PetDosageChart

Zofran (Ondansetron) Dosage for Cats

Serotonin (5-HT3) antagonist antiemetic ⏱ Onset: 30-60 minutes (oral), 10-15 minutes (injectable) ⏳ 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.

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Zofran Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 0.5mg 1mg 1.5mg every 8-12 hours
4 lbs (1.8 kg) 1mg 1.5mg 2mg every 8-12 hours
5 lbs (2.3 kg) 1mg 1.5mg 2.5mg every 8-12 hours
6 lbs (2.7 kg) 1.5mg 2mg 2.5mg every 8-12 hours
7 lbs (3.2 kg) 1.5mg 2.5mg 3mg (4mg tablet) every 8-12 hours
8 lbs (3.6 kg) 2mg 2.5mg 3.5mg (4mg tablet) every 8-12 hours
9 lbs (4.1 kg) 2mg 3mg (4mg tablet) 4mg (4mg tablet) every 8-12 hours
10 lbs (4.5 kg) 2.5mg 3.5mg (4mg tablet) 4.5mg (4mg tablet) every 8-12 hours
12 lbs (5.4 kg) 2.5mg 4mg (4mg tablet) 5.5mg every 8-12 hours
14 lbs (6.3 kg) 3mg (4mg tablet) 4.5mg (4mg tablet) 6.5mg every 8-12 hours
16 lbs (7.3 kg) 3.5mg (4mg tablet) 5.5mg 7.5mg (2 × 4mg) every 8-12 hours
18 lbs (8.2 kg) 4mg (4mg tablet) 6mg 8mg (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

What is Zofran (Ondansetron) used for in cats?

nausea vomiting chemotherapy-induced nausea post-anesthetic nausea motion sickness

How to give Zofran 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.

Available Forms

tablet, injectable, oral dissolving tablet

Give with Food?

No — can be given without food

Side effects of Zofran in cats

Common side effects

constipation
mild sedation
headache
mild diarrhea

Serious side effects

  • cardiac arrhythmias (QT prolongation)
  • serotonin syndrome with other serotonergic drugs
  • severe constipation
  • hypersensitivity reaction

When to call the vet

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

  • Vomiting continues despite ondansetron treatment
  • Signs of dehydration (sunken eyes, dry gums, skin tenting)
  • Blood in vomit or stool
  • Lethargy or inability to keep water down
  • Rapid or irregular heartbeat

Related Medications for Cats

NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart
Serotonin Antagonist and Reuptake Inhibitor (SARI)

Desyrel

Trazodone

For Anxiety and fear reduction

View dosage chart
H2 receptor antagonist

Pepcid

Famotidine

For stomach acid reduction

View dosage chart
Antihistamine (H1 Receptor Antagonist)

Atarax

Hydroxyzine

For Allergic dermatitis and itching

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 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.

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