By Rania Gollakner, BS, DVM, MPH

What is ondansetron?

Ondansetron (brand names: Zofran®, Zuplenz®) is an antiemetic used to treat severe nausea and vomiting in dogs and cats.

Its use in cats and dogs to treat vomiting is 'off label' or 'extra label'. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their direction may be significantly different from those on the label.

How is ondansetron given?

Ondansetron is given by mouth in the form of a tablet or liquid, and it may be given with or without food. If vomiting occurs when dosed on an empty stomach, give future doses with food or a treat. Liquids should be measured carefully. Some tablets are dissolvable, so be sure your hands are dry before handling these tablets.

Ondansetron can also be compounded into a topical gel, and gloves must be worn when applying this topical gel. In the hospital setting, it is also administered via injectable liquid and given in the vein, muscle, or under the skin.

This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects are uncommon. Rare side effects may include constipation, sleepiness, or head shaking. Rare but serious side effects include abnormal heart rhythms and low blood pressure, which may cause fainting/collapse or severe lethargy.

This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Ondansetron should not be used in pets that are allergic to it. It should be used cautiously in pets with gastrointestinal blockage, certain abnormal heart rhythms, or liver disease. Ondansetron should be used with caution in pregnant or lactating pets as safety has not been clearly established.

Some breeds of dogs (e.g., collies, sheepdogs, and collie- or sheepdog-cross breeds) are more sensitive than others to medications. This is typically due to a specific genetic mutation (MDR1) that makes them less able to tolerate high doses of certain medications. Therefore, ondansetron should be used cautiously in these cases.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with ondansetron: apomorphine, cisplatin, cyclophosphamide, certain heart medications, serotonergic drugs, or tramadol.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

There is no specific monitoring that needs to be done while your pet is taking this medication. Your veterinarian may monitor your pet to be sure that the medication is working.

How do I store ondansetron?

This medication should be stored at room temperature between 2°C and 30°C (36°F and 86°F) in a tight container and protected from light and moisture.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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