Ondansetron for Dogs and Cats: Uses and Side Effects

Ondansetron is a prescription medication veterinarians use to treat nausea and vomiting in dogs and cats.

Also known by the human brand name Zofran®, ondansetron is prescribed extra-label for pets and may be used alone or with other medications.

Here’s how ondansetron for dogs and cats works, when it may be prescribed, possible side effects, and important administration and safety guidance.

What Is Ondansetron?

Ondansetron is a prescription medication used to treat and prevent nausea and severe vomiting in dogs and cats.

Veterinarians may prescribe ondansetron for:

• Dogs with parvovirus
• Dogs undergoing chemotherapy
• Dogs with vestibular disease, a group of conditions that can cause balance problems
• Cats with chronic kidney disease
• Dogs or cats at risk of nausea and vomiting before anesthesia

Available formulations: Ondansetron may be used alone but is more often combined with other medications. It is available as an oral tablet, orally disintegrating tablet, and oral solution. An injectable form may also be administered under direct veterinary supervision in a hospital.

Your veterinarian will determine the appropriate formulation and combination of medications based on your pet’s condition and symptoms.

Extra-label use: Ondansetron is FDA-approved for people under the brand names Zofran® and Zofran® ODT, as well as in generic form. It is not FDA-approved as a veterinary medication, but veterinarians may legally prescribe it to animals extra-label or off-label when appropriate.

Human and veterinary doses and side effects may differ. Never give your pet ondansetron or any other medication prescribed for a person unless your veterinarian specifically instructs you to do so.

Compounded ondansetron: In some cases, your veterinarian may recommend a compounded formulation. This may be appropriate if:

• Your pet has difficulty taking the commercially available formulation
• The required dosage strength is not commercially available
• Your pet is allergic to an ingredient in the available medication

Compounded medications are not FDA-approved. They are prepared by a veterinarian or licensed pharmacist to meet an individual patient’s specific needs.

Safety Considerations for Ondansetron

Ondansetron should be used cautiously in dogs with the MDR1 gene mutation and may not be appropriate for pets with certain allergies, medical conditions, or medication interactions.

Talk with your veterinarian before giving ondansetron if your pet:

• Has the MDR1 gene mutation, which can make it harder for some dogs to process medications such as ondansetron
• Has a known sensitivity or allergy to ondansetron
• Has liver disease or another medical condition that may affect medication safety
• Takes other medications that could interact with ondansetron

Tell your veterinarian about all of your pet’s medications, supplements, and medical conditions so they can determine whether ondansetron is appropriate.

How Ondansetron Works

Ondansetron works by blocking serotonin signals that trigger nausea and vomiting.

Serotonin is a naturally occurring neurotransmitter found in the gastrointestinal tract and brain. It sends signals from the gastrointestinal tract to the brain's vomiting center, called the chemoreceptor trigger zone (CRTZ), which can trigger nausea and vomiting.

By blocking serotonin's effects, ondansetron helps reduce nausea and vomiting.

How To Give Ondansetron

Give ondansetron exactly as directed by your veterinarian. It may be given with or without food.

Always follow the directions on the prescription label or the instructions provided by your veterinarian.

Missed a Dose?

If you miss a dose of ondansetron, contact your veterinarian for guidance. In many cases, they may recommend giving the missed dose when you remember.

However, if it is almost time for your pet's next scheduled dose, they may advise skipping the missed dose and resuming the normal dosing schedule.

Do not give extra or double doses.

Ondansetron Side Effects

Ondansetron is generally well tolerated by most dogs and cats, but side effects can occur.

Possible side effects include:

• Constipation
• Diarrhea
• Extrapyramidal clinical signs (such as head shaking)
• Arrhythmias
• Sedation
• Hypotension

Human Side Effects

Although ondansetron is also prescribed for people, human and veterinary doses may differ.

If you accidentally ingest this medication, contact your physician immediately or call the National Poison Control Center at 800-222-1222.

When To Call Your Veterinarian

Contact your veterinarian if:

• Your pet develops severe side effects.
• You suspect your pet has received an overdose.
• Your pet's condition worsens or does not improve with treatment.
• You have additional questions or concerns about using ondansetron.

Ondansetron Overdose

An overdose of ondansetron can cause serious side effects and requires immediate veterinary attention.

Signs of an overdose may include:

• Constipation
• Diarrhea
• Grogginess
• Head shaking
• Elevated liver values
• Abnormal heart rhythm
• Abnormally low blood pressure

If you suspect an overdose, contact your veterinarian immediately, seek emergency veterinary care, or call an animal poison control center. Consultation fees may apply.

• Pet Poison Helpline: (855) 764-7661
• ASPCA Animal Poison Control: (888) 426-4435

How To Store Ondansetron

Store ondansetron according to the manufacturer's instructions to help maintain its safety and effectiveness.

Storage instructions:

• Store oral ondansetron at controlled temperatures between 36 F and 86 F (2 C–30 C).
• Store injectable ondansetron between 36 F and 77 F (2 C–25 C).
• Store compounded ondansetron according to the instructions provided by the compounding pharmacy.
• Keep the container tightly closed to protect the medication from moisture and light.
• Keep out of reach of children and pets.