Basic Information
Acepromazine maleate is a phenothiazine derivative that is used as a
neuroleptic agent in veterinary medicine. It is a commonly used tranquilizer for
dogs, cats, and horses. Phenothiazines decrease dopamine levels and depress some
portions of the reticular activating system. Acepromazine is metabolized by the
liver and excreted in the urine.
In addition to tranquilization, acepromazine has multiple other important
systemic effects including anti-cholinergic, anti-emetic, antispasmodic,
antihistaminic, and alpha-adrenergic blocking properties. Acepromazine causes
hypotension due to decreased vasomotor tone. It may change heart and respiratory
rate and thermoregulatory ability allowing for either hypo- or hyper-thermia.
Acepromazine may be given intramuscularly, intravenously, or orally. It
provides no analgesia and the tranquilizing effect of the drug can be overcome
unexpectedly, particularly by sensory stimulation. Acepromazine usually is less
effective if given after the animal is excited. There is a great deal of
individual variability in the response to acepromazine and despite being a very
commonly used medication there are important species and even breed differences
in response to acepromazine that need to be taken into consideration (see
precautions).
Dogs and Cats
Acepromazine is one of the most commonly used tranquilizers for dogs and
cats. It decreases anxiety, causes central nervous system depression, and a drop
in blood pressure and heart rate. It may be used in conjunction with atropine as
a pre-operative medication for anxiety and for its antidysrhythmic effects. Oral
acepromazine may be prescribed to prevent motion sickness, to temporarily reduce
itching and scratching due to allergies, or prior to office visits, nail
trimming, or grooming appointments if the animal is too fractious to handle
safely without sedation. Some veterinarians are reluctant to prescribe
acepromazine for travel anxiety when the animal may be exposed to temperature
extremes, such as during plane travel or when there may be limited access to
veterinary care. Other drugs used for travel anxiety/motion sickness include
meclizine, diphenhydramine, and diazepam. Occasionally, animals (particularly
cats) may have a paradoxical response to acepromazine and become excited or
aggressive.
Horses
Acepromazine is one of the most commonly used tranquilizers for horses. It
may be used alone or in combination with other sedative drugs such as xylazine,
detomidine, or butorphanol. Because acepromazine lowers blood pressure by
dilating small blood-vessels, it sometimes is prescribed in the early treatment
of laminitis in order to diminish vasospasm, and possibly to improve circulation
within the hoof.
Acepromazine is also used in horses that are prone to exertional
rhabdomyolysis both as a preventive and as a part of the treatment due to its
vasodilatory properties. When acepromazine is used to treat more severe cases of
exertional rhabdomyolysis, intravenous fluids may be desirable to increase
hydration and to support renal function.
Onset of action of acepromazine varies with route of administration; oral
acepromazine may take 30 minutes to one hour. The effects of acepromazine will
last from one to four hours, but this varies significantly with dose and among
individual horses. Acepromazine is a prohibited substance in most sanctioned
competition. Oral administration or long-term, repeated dosing may increase
detection time.
Side Effects
- Common: Acepromazine will cause hypotension, decreased respiratory rate, and
bradycardia. Dogs are particularly sensitive to cardiovascular side-effects but
cardiovascular collapse also has occurred in cats. Sudden collapse, decreased or
absent pulse and breathing, pale gums, and unconsciousness may occur in some
animals.
- Rare: fatal interactions with anesthetics have been reported.
- Acepromazine will cause a dose-dependent decrease in hematocrit in both dogs and
horses. This effect occurs within 30 minutes of administration and may last for
12 hours or more. The hematocrit in horses may decrease by as much as 50%.
- Penile paralysis is a rare but recognized adverse side-effect of acepromazine
use in the horse. This drug should be avoided in breeding stallions.
Precautions
- Acepromazine lowers blood pressure. It should not be used in animals that are
dehydrated, anemic, or in shock.
- Acepromazine should be avoided or used with
extreme caution in older animals or those with liver disease, heart disease,
injury, or debilitation. If it is used in these animals, it should be given in
very small doses. In some older animals, a very small dose can have a marked and
very prolonged effect.
- Acepromazine should not be used in animals with a history
of epilepsy, those prone to seizures, or those receiving a myelogram because it
may lower the seizure threshold.
- Acepromazine should not be used in animals with
tetanus or strychnine poisoning.
- Acepromazine should be avoided in pregnancy or
lactation. It should be avoided or used with extreme caution in young animals
due to its effects on an animal's ability to thermo regulate.
- Dogs: Giant breeds
and greyhounds may be extremely sensitive to acepromazine, while terriers may
require higher doses. Brachycephalic breeds, especially Boxers, are particularly
prone to cardiovascular side-effects (drop in blood pressure and slow
heart-rate). Acepromazine should be avoided or used with great caution in these
breeds.
- Horses: Draft-horse breeds are especially sensitive to most sedatives
including acepromazine. Pony breeds do not appear to differ from horses in their
responses to acepromazine.
Drug Interactions
- Animals receiving acepromazine will require lower doses of barbiturates,
narcotics and other anesthetics. These combinations increase central nervous
system depression.
- Antidiarrheal mixtures like Kaopectate® and Pepto-Bismol® ,or
antacids decrease the absorption of oral acepromazine.
- Acepromazine should not
be used within one month of deworming with organophosphate compounds.
- Quinidine,
epinephrine, propanolol, procaine hydrochloride, and phenytoin all have been
shown to have significant drug-interactions with phenothiazines. Further
information should be sought before concomitant administration.
Overdose
- Overdose will cause excessive sedation, slow respiratory and heart rate, pale
gums, unsteady gait, poor coordination, and inability to stand. It also may
cause sudden collapse, unconsciousness, seizures, and death.
- Oral overdose
should be treated by emptying the stomach along with monitoring and other
supportive care.
- Phenylephrine and norepinephrine are the drugs-of-choice to
treat acepromazine-induced hypotension. Barbiturates or diazepam may be used to
treat seizures associated with overdose.