Ondansetron for cats: Dosage, uses & side effects

In this article:

• Uses
• Safety & side effects
• Dosage
• How to give your cat ondansetron
• Ondansetron alternatives
• FAQs

In this article

• Uses
• Safety & side effects
• Dosage
• How to give your cat ondansetron
• Ondansetron alternatives
• FAQs

Ondansetron is a prescription anti-nausea medication that veterinarians may use off-label in cats. It can help manage nausea and vomiting caused by conditions such as pancreatitis or treatments such as chemotherapy. This article explains when veterinarians use ondansetron for cats, typical dosages, possible side effects, and how to give it safely. 

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What is ondansetron used for in cats?

Veterinarians may use ondansetron when a cat has significant nausea or vomiting, including symptoms associated with chemotherapy or other drug treatments and pancreatitis. 

Ondansetron belongs to a family of drugs called 5-HT3 receptor antagonists, or serotonin antagonists. It blocks 5-HT3 serotonin receptors involved in the vomiting response, including receptors in the chemoreceptor trigger zone of the brain and on nerves in the gastrointestinal tract. By interfering with these signals, ondansetron helps reduce vomiting.

Ondansetron typically begins working within one to two hours.

Chemotherapy and drug-induced vomiting

Cancer is common in cats, and treatment may include chemotherapy, radiation therapy, surgery, or other interventions. For chemotherapy-related vomiting, a veterinary reference lists ondansetron at 0.5 mg/kg by mouth or intravenously every 12 to 24 hours and notes that it may be given about 30 minutes before chemotherapy. 

Pancreatitis

Pancreatitis is inflammation of the pancreas that can range from mild to severe. Nausea and vomiting can occur in cats with pancreatitis, and anti-nausea medications can help cats tolerate food and reduce fluid and electrolyte losses.

Ondansetron may be given by mouth or intravenously as part of supportive treatment for pancreatitis. It does not treat the pancreatic inflammation itself and may be used alongside fluids, pain medication, nutritional support, and other treatments.

Vomiting

Occasional vomiting may not require anti-nausea medication, but cats with frequent or persistent vomiting may need treatment to reduce fluid loss and discomfort. Ondansetron is one of the medications veterinarians may use for acute, frequent, or severe vomiting, depending on the underlying cause. 

Is ondansetron safe for cats?

Ondansetron is generally well tolerated in cats when given under a veterinarian’s direction, and side effects are uncommon. However, it may not be appropriate for every cat, especially if they have had an allergic reaction to ondansetron or other serotonin antagonists like dolasetron or granisetron. 

Liver disease can reduce how quickly ondansetron is cleared from the body, so a veterinarian may adjust treatment accordingly. In humans, ondansetron’s dosage is reduced in severe liver impairment, but specific dosage adjustments for cats depend on the veterinarian’s assessment. 

Ondansetron can also be used to manage nausea and vomiting associated with kidney disease, but its effects may last longer in pets with impaired kidney function. 

Side effects of ondansetron in cats

Though uncommon, possible side effects of ondansetron in cats are:

• Constipation
• Sleepiness and drowsiness
• Involuntary muscle movements like head shaking
• Low blood pressure (hypotension)

Low blood pressure is a rare but potentially serious side effect. Signs may include fainting, collapse, or severe lethargy. 

Interactions of ondansetron with other pet meds

Ondansetron has relatively few major drug interactions. These include:

• Certain medications that affect heart rhythm, such as amiodarone, cisapride, and sotalol
• Serotonergic medications, including the opioid pain reliever tramadol

Tell the veterinarian about all prescription drugs, over-the-counter medications, supplements, and herbal remedies the cat is on. 

Ondansetron dosage for cats

Ondansetron dosages for cats vary depending on the condition being treated, the route of administration, and the veterinarian’s recommendation. Published veterinary dosages generally range from 0.1–1 mg/kg, with doses given at different intervals depending on the situation. 

Ondansetron dosage chart for cats
Indication	Possible dosage
Severe vomiting	0.1–1.0 mg/kg given as an intravenous infusion every six to 12 hours as needed
Vomiting associated with severe pancreatitis	0.1–1 mg/kg given by mouth or intravenously every 12 to 24 hours
Nausea (as an antiemetic)	0.1–0.2 mg/kg given by mouth every 12 hours or every 24 hours

Some veterinary references recommend 0.5–1 mg/kg by mouth or intravenously every eight to 12 hours. Your veterinarian will determine the appropriate dose and route based on the cat’s condition. 

Ondansetron may be administered by a veterinarian in a clinical setting or prescribed for use at home. When oral treatment is appropriate, veterinarians may prescribe a commercially available human formulation or have the medication compounded into a specific dose or flavored liquid.

Human ondansetron is available in several dosage forms, including tablets, orally disintegrating tablets, and oral solution. Pet owners should use only the formulation and dose prescribed by their veterinarian.

How to give your cat ondansetron

Ondansetron may be given by mouth at home as a tablet or liquid. In a veterinary hospital, it can also be given by injection into a vein, muscle, or under the skin. 

When giving ondansetron at home: 

• Follow the veterinarian’s dosing instructions and schedule.
• If you don’t know how to give your cat a tablet, ask the veterinarian or veterinary technician to demonstrate the technique.
• If giving a pill is difficult, a compounding pharmacy may be able to prepare an ondansetron oral liquid.
• Ondansetron can be given with or without food. If your cat vomits after receiving it on an empty stomach, ask the veterinarian whether future doses should be given with food.
• Measure liquid medication carefully with the provided oral syringe and follow the product label for instructions, such as whether the liquid should be shaken before use.
• If your cat vomits after taking a dose, contact the veterinarian before giving another dose.

Ondansetron alternatives for cats

Ondansetron may not be the first choice for every case of nausea or vomiting in cats. It is often used for persistent or refractory vomiting and is not typically used for motion sickness. Cats with motion sickness may be treated with other medications, such as maropitant.

If a cat cannot take ondansetron, veterinarians have other treatment options, depending on the cause of the vomiting. These may include:

• Maropitant (available for cats as brand-name Cerenia)
• Phenothiazines such as prochlorperazine or chlorpromazine
• Metoclopramide

Antacids, medications that protect the stomach lining, and appetite stimulants may also be used to treat the cause of nausea or vomiting. These include drugs such as omeprazole, famotidine, sucralfate, mirtazapine, or cisapride. 

Bottom line

Ondansetron is an anti-nausea drug used to reduce severe or persistent nausea and vomiting in cats. It generally has few side effects. Ondansetron may be given by a veterinarian as an injection or prescribed as an oral medication for use at home. In those cases, pet owners should carefully follow the veterinarian’s instructions about dosing. 

Frequently asked questions

Can cats overdose on ondansetron?

An ondansetron overdose can cause serious problems. Although specific overdose effects in cats are not well established, excessive ondansetron has caused effects such as low blood pressure, severe constipation, and serotonin syndrome in humans. 

What should I do if I give my cat too much ondansetron?

If you suspect your cat has received too much ondansetron, contact the veterinarian or an emergency veterinary hospital immediately. 

Can I give my cat ondansetron every day?

Ondansetron can be given to a cat every day if prescribed by a veterinarian. Depending on the condition being treated, a veterinarian may prescribe it on a regular schedule or as needed. Follow the prescribed dose and schedule rather than giving ondansetron more or less often without veterinary guidance.