Ondansetron for dogs: Dosage and safety

In this article:

• What is ondansetron used for in dogs?
• Is ondansetron safe for dogs?
• Side effects of ondansetron in dogs
• Interactions of ondansetron with other pet meds
• Ondansetron dosage for dogs
• Ondansetron alternatives for dogs

In this article

• What is ondansetron used for in dogs?
• Is ondansetron safe for dogs?
• Side effects of ondansetron in dogs
• Interactions of ondansetron with other pet meds
• Ondansetron dosage for dogs
• Ondansetron alternatives for dogs

Ondansetron (Zofran) is a powerful anti-nausea drug that prevents and reduces nausea and vomiting. It belongs to a small family of drugs called 5-HT3 receptor antagonists. Also called serotonin antagonists, these drugs reduce nausea and vomiting by blocking the chemical that transmits nerve signals in the gastrointestinal tract and the part of the brain that controls nausea (the chemoreceptor trigger zone). In human patients, ondansetron is used to prevent nausea during cancer chemotherapy or radiation therapy. Its use in animals is considered off-label (not approved by the Food and Drug Administration). 

Save up to 80% on Ondansetron with SingleCare

Different pharmacies offer different prices for the same medication. SingleCare helps find the best price for you.

Ondansetron 4 mg (10 Tablet)

23666 - Hampton, VA

$5.11

i Price with signup

Get free coupon

$5.11

i Price with signup

Get free coupon

See Ondansetron prices at all pharmacies

What is ondansetron used for in dogs?

Veterinarians commonly use ondansetron for dogs to treat severe or frequent nausea and vomiting that can’t be managed with other anti-nausea drugs. 

Chemotherapy

As with humans, dogs often experience nausea and vomiting after chemotherapy doses. Veterinarians can control these side effects by giving the dog ondansetron before and after each chemotherapy dose. Treatment usually involves a single dose or a handful of doses administered over a few days. 

Vomiting

Most of the time, ondansetron is not a first-line drug if a dog is nauseous or vomiting unless the vomiting is severe and continuous. In those cases, ondansetron or similar drugs are often the first choice for treatment. It’s important to treat severe or frequent vomiting with potent antiemetics as early as possible to stop the vomiting and prevent dehydration.

Diarrhea

Ondansetron can also help relieve diarrhea in dogs. That’s because the way ondansetron works in quelling nausea also slows down intestinal contractions and reduces the water content of stools. This is more often seen as a side effect of ondansetron in dogs, but in dogs experiencing diarrhea and nausea, ondansetron can help with both. For diarrhea, it’s only used as an adjunct treatment, meaning it’s prescribed with other antidiarrheal medications, not on its own.

Is ondansetron safe for dogs?

Ondansetron has relatively few side effects in dogs, and severe side effects are rare. However, no medicine is 100% safe in all dogs.

Ondansetron should never be given to dogs who:

• Have had an allergic reaction to ondansetron or similar drugs like granisetron or dolasetron
• Have a large intestine that’s not working (ileus)
• Have an enlarged stomach (gastric distention)

Ondansetron may be risky in dogs with liver disease. The liver breaks down ondansetron. If it’s not working well, the drug can build up in the dog’s blood and cause side effects. In these cases, the veterinarian will probably reduce or space out doses over longer times. 

Ondansetron can be safely given to dogs with kidney disease. 

Side effects of ondansetron in dogs

The most common side effects of ondansetron in dogs are:

• Constipation
• Sleepiness and drowsiness
• Head shaking 
• Low blood pressure (hypotension)

In one study, ondansetron used in very high doses was associated with a change in the electrical signals within the heart. No changes in blood flow or symptoms were noted in these dogs, but vets may use lower doses in dogs who have underlying heart disease.

Interactions of ondansetron with other pet meds

All drugs interact with other drugs, so the veterinarian should know about all prescription drugs as well as any over-the-counter medications, supplements, or at-home remedies (like CBD) given to the dog. 

Ondansetron has relatively few drug interactions that veterinarians worry about. These include:

• Drugs that affect the heart’s rhythm
• The narcotic painkiller tramadol, as the combination of tramadol and ondansetron may cause both drugs to be less effective
• Apomorphine, a drug that induces vomiting (emetic) in dogs

Ondansetron dosage for dogs

Ondansetron doses vary based on the treated condition and whether the medication is given orally or injected. Recent studies show oral ondansetron is not well absorbed in dogs, causing injections of ondansetron to be more often chosen by veterinarians.

Dosages also vary depending on the source. The Merck Veterinary Manual gives a standard dose of 0.1–0.2 mg/kg when given orally and 0.1–0.15 as an intravenous injection. These dosages appear elsewhere in veterinary literature as well.

On the other hand, Plumb’s Veterinary Drug Manual lists the following ondansetron dosages for dogs:

• For nausea or vomiting due to chemotherapy: 0.5–1 mg/kg given by mouth every 8–12 hours OR 0.1–0.5 mg/kg intravenous infusion every 8 hours or 30 minutes before administering cisplatin
• To control severe or frequent vomiting: 0.1–1 mg/kg intravenous injection every 8–12 hours 
• As an antiemetic: 0.1–1 mg/kg given by mouth every 12–24 hours OR 0.1–1 mg/kg IV injections every 6–12 hours

Ondansetron is often used for chemotherapy or serious vomiting, so there’s a good chance a veterinary professional will administer most or all the doses. Pet parents sent home with ondansetron for dogs will be given either human versions of ondansetron or oral formulations prepared by a compounding pharmacy. Dosage forms include tablets, orally disintegrating tablets, and liquid oral solutions. A compounding pharmacy can also make a transdermal gel to apply to the dog’s skin, but research suggests this may not be an effective way to give animals ondansetron. 

Can dogs overdose on ondansetron?

Do not give a pet too much ondansetron. Too much ondansetron has caused sudden, short-lived blindness, low blood pressure, and severe constipation in human patients. There is also a risk of serotonin syndrome, a potentially serious complication of taking drugs like ondansetron that affects serotonin levels. Call an animal poison control center or a veterinarian if too much ondansetron is given to a dog. Take the dog to a veterinarian or animal hospital if the dog starts showing unusual symptoms.

Can I give my dog ondansetron every day?

Ondansetron can be given to a dog daily for the length of time prescribed by the veterinarian, but it’s typically a short-term treatment. In humans, it’s often given in a single dose or a handful of doses over one or two days. 

How to give your dog ondansetron

Among pet meds, ondansetron is relatively easy to give to a dog because the treatment only lasts a few days. Here are some tips for giving your dog ondansetron:

• Follow all the veterinarian’s instructions, and provide ondansetron with or without food.
• Do not miss doses. The dog will usually need a dose every eight or 12 hours.
• Since ondansetron is given to dogs who are nauseous or vomiting, the dog may vomit up a dose. The dose may not be to blame. Ask the veterinarian what to do in case this happens.
• If you have problems giving your dog tablets, you can mix the tablet with food. A veterinarian may also be able to supply you with ondansetron in an easier dosing format.
• If you are using the oral solution:
  • There is no need to shake the bottle before measuring a dose.
  • Use a calibrated syringe to measure the dose—the veterinarian should supply you with one.
• If you use ondansetron gel, wear gloves when applying it to the dog’s skin.
• Store ondansetron at room temperature, protected from light.

Ondansetron alternatives for dogs

Veterinarians have a broad range of anti-nausea drugs to choose from. They span many different drug classes, so they work in very different ways. Veterinarians will select the most suitable medication for a dog’s specific condition.

Ondansetron works very fast, dramatically reducing the incidence of vomiting and signs of nausea, such as lip licking, in a dog. For this reason, ondansetron is the drug of choice to treat severe or frequent vomiting. Other top-line choices include dolasetron and maropitant. All are powerful anti-nausea drugs. When a dog has severe or frequent vomiting, it’s important to use these potent anti-nausea drugs as early as possible. 

For nausea and vomiting due to chemotherapy, metoclopramide or maropitant are the standard treatment options in addition to ondansetron. 

Bottom line: Ondansetron is safe for dogs

Ondansetron is a first-choice treatment for severe or frequent vomiting in dogs and is commonly used to control chemotherapy-induced nausea and vomiting. It rapidly and dramatically reduces vomiting and increases the dog’s comfort. It has few side effects, and treatment lasts for a short time. If you are sent home with ondansetron tablets or liquid, give each dose as instructed and on time to keep the dog comfortable.