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Ondansetron (Zofran®)

By: Dr. Nicholas Dodman

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  • Ondansetron is a drug that selectively inhibits serotonin 5HT3 receptors. 5HT3 receptors are located on vagal nerve terminals, enteric neurons in the GI tract, and centrally in the brain in a region called the chemoreceptor trigger zone.
  • Ondansetron is used as an antiemetic, particularly to prevent severe vomiting associated with cancer chemotherapy or radiotherapy.
  • Following oral administration, ondansetron is well absorbed.
  • Ondansetron has does not stimulate gastric or intestinal peristalsis, and has little effect on blood pressure, heart rate or rhythm.
  • Ondansetron is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Zofran® (Glaxo Smith Kline).
  • Veterinary formulations: None

    Uses of Ondansetron

    Uses include:

  • As an antiemetic for treatment of severe vomiting resulting from cancer therapy or poisoning
  • Treatment of sleep-apnea in bulldogs
  • Treatment of pruritus occurring secondary to spinal or epidural opioids

    Precautions and Side Effects

  • Ondansetron should not be used in animals with known hypersensitivity or allergy to the drug.

    Drug Interactions

    Ondansetron may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with ondansetron. Possible interactions may include:

  • Injectable ondansetron should only be mixed with solutions with which it has been shown to be compatible. It should not be mixed with any alkaline solutions or a precipitate may form.
  • Rifampin decreases plasma levels of ondansetron and will thus reduce its efficacy.

    How Ondansetron is Supplied

  • Ondansetron is available in 4 mg, 8 mg, 24 mg tablets.
  • Ondansetron 4 mg/5 mL oral solution is also available.
  • The injectable form of ondansetron may vary. Some injectable forms include a 2 mg/mL concentration in a 20 mL multidose vials and a 32 mg/50 mL concentration.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • Doses of may vary widely depending on the reason for prescribing.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects.
  • In dogs, the usual dose is 0.05 to 0.5 mg per pound (0.1 to 1.0 mg/kg) orally every 12 to 24 hours. The intravenous dose is 0.05 to 0.1 mg per pound (0.1 to 0.2 mg/kg).
  • In cats, the usual dose is 0.11 mg per pound (0.22 mg/kg) every 8 to 12 hours.

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