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Chlorpromazine (Thorazine®)

By: Dr. Dawn Ruben

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  • Chlorpromazine belongs to a class of drugs known as phenothiazine derivatives. Other related drugs in this class include acepromazine and prochlorperazine.
  • The exact mechanism of action of the phenothiazine derivatives is not completely understood. The drugs work by somehow blocking dopamine receptors in the nervous system and may even inhibit the release of dopamine.
  • These drugs are thought to affect the part of the brain responsible for controlling body temperature, metabolic rate, vomiting, blood pressure and alertness.
  • Compared to other phenothiazines, chlorpromazine has moderate sedative effects and moderate to strong anti-vomiting effects.
  • Chlorpromazine 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: Thorazine® (SKF), Ormazine® (Hauck) and various generics.
  • Veterinary formulations: None

    Uses of Chlorpromazine

  • Chlorpromazine is used to reduce nausea and vomiting.
  • Infrequently, chlorpromazine may be used as a sedative.

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, chlorpromazine can cause side effects in some animals.
  • Chlorpromazine should not be used in animals with known hypersensitivity or allergy to the drug.
  • Chlorpromazine should be avoided in animals with glaucoma, low blood pressure or shock.
  • This drug should be used with caution in animals with liver disease, heart disease or older patients.
  • Chlorpromazine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with chlorpromazine. Such drugs include certain narcotics, barbiturates, propranolol, epinephrine and some anti-diarrheal medications.
  • Constipation, sedation and low blood pressure may occur after administration of chlorpromazine.
  • In cases of overdose, chlorpromazine can cause tremors and drooling.

    How Chlorpromazine is Supplied

  • Chlorpromazine is available in 10 mg, 25 mg, 50 mg, 100 mg and 200 mg tablets.
  • Chlorpromazine is also available in 30 mg, 75 mg, 150 mg, 200 mg and 300 mg extended release capsules. An oral solution is available in 2 mg/ml syrup and 30 mg/ml concentrate, both in 120 ml bottles.
  • Rectal suppositories of 25 mg and 100 mg are available.
  • Injectable chlorpromazine is also available in 25 mg/ml concentration in 1 ml and 2 ml ampules as well as a 10 ml bottle.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • To treat nausea and vomiting in dogs, chlorpromazine is dosed at 0.12 to 0.25 mg per pound (0.25 to 0.5 mg/kg) subcutaneously or intramuscular every 6 to 24 hours. It can also be given intravenous at a dose of 0.02 to 0.05 mg per pound (0.05 to 0.1 mg/kg) every 6 to 8 hours as needed.
  • To treat nausea and vomiting in cats, chlorpromazine is dosed at 0.005 to 0.012 mg per pound (0.01 to 0.025 mg/kg) intravenous every 6 to 8 hours as needed.
  • If vomiting is not severe, chlorpromazine can be administered orally at a dose of 0.05 to 1 mg per pound (0.1 to 2.2 mg/kg) 1 to 4 times daily.
  • For sedation, chlorpromazine is dosed at 1.5 mg per pound (3 mg/kg) by mouth once or twice daily. The injectable sedative dose is 0.25 mg per pound (0.5 mg/kg) intramuscular or intravenous once or twice daily.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.

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