By Rania Gollakner, BS, DVM, MPH

What is chlorpromazine?

Chlorpromazine (brand names: Thorazine®, Largactil®, Chlorprom®, Chlorpromanyl®) is a phenothiazine sedative and anti-vomiting medication used as a sedative or to treat motion sickness, particularly in cats.

Its use in cats and dogs, to treat vomiting or as a sedative 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 directions may be significantly different from those on the label.

How is chlorpromazine given?

Chlorpromazine is given by mouth in the form of a tablet or liquid. It can also be given by injection in the hospital setting. Measure the liquid form of this medication carefully. Do not administer this medication to your pet if the liquid changes to a dark color or if chunks form in the liquid.  Do not get chlorpromazine on your hands as skin irritation or a rash may occur. Your pet’s urine may temporarily change color to pink or a reddish-brown color. 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?

Give the missed dose as soon as you remember, and then wait the recommended amount of time between doses. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects include tiredness, low blood pressure, low heart rate, or a tendency to react or startle to noises. In cats, higher doses can cause tremors, shivering, rigidity, lethargy, diarrhea, loss of anal sphincter tone, and loss of certain reflexes. Serious side effects include coma, agitation, seizures, abnormal heart rhythms, or dangerously low blood pressure.

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?

Chlorpromazine should not be used in pets that are allergic to it or in pets with low blood pressure. It should be used cautiously in pets that are generally debilitated or have liver disease, heart disease, seizures, or aggressive behavior. Use cautiously in pregnant or lactating animals.

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, chlorpromazine should be used cautiously in these cases and a lower dose should be considered.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with chlorpromazine: acetaminophen, antacids, antidiarrheal mixtures, bromocriptine, buspirone, cabergoline, calcium channel blockers, CNS depressant agents, desmopressin, diazoxide, dipyrone, dopamine, doxorubicin, epinephrine, laxatives, loop diuretics, opiates, organophosphate agents, paraquat, phenytoin, physostigmine, propranolol, QT prolonging agents, quinidine, or tricyclic antidepressants.

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?

Heart rate and rhythm, blood pressure, and body temperature should be monitored. Monitor your pet to be sure that the medication is working and that the dose is adequate or not excessive.

How do I store chlorpromazine?

Store at room temperature, protected from light and moisture. Do not freeze the liquid solution.

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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