Acepromazine: Why I'm not a big fan when it comes to sedation via 'ace'

Patty Khuly, DVM
Written by:
Published: October 22, 2009
Acepromazine: Why I'm not a big fan when it comes to sedation via 'ace'

In this week’s post on my Slumdog’s recent need for sedation, the tranquilizer known as acepromazine was addressed in response to a round of questions. As in––Why wouldn’t you use this tried and true veterinary drug on your own dog?

When I offered my answer, I received a comment urging me to be more clear about “ace” so that pet owners wouldn’t get a one-sided view of this popular drug. In response, I thought it wise to provide a more complete rendering of the issues involved in its usage––especially since acepromazine is veterinary medicine’s go-to tranquilizer.

This drug is used in a variety of ways in veterinary medicine. Here are the most commonly applied indications in cat and dog medicine:

  • as an oral sedative for travel, during storms and before grooming or veterinary visits
  • as an injectable tranquilizing agent to address aggressive, fractious or disruptive behaviors in hospital settings
  • in small doses (and typically in combination with an opiate), as an injectable anesthetic pre-medication
  • in small doses in combination with pain relievers post operatively to enhance the effect or lower the dose of the analgesic

In the last two cases, I employ acepromazine often (though by no means always). Pre-op, it’s used to lower the dose of anesthetic induction agents to follow, lower blood pressure slightly, reduce the potential for arrhythmias (abnormal heart rhythms) and vomiting, and to confer mild relaxation prior to the procedure. Post-op, its synergistic effects with drugs like opiates mean that a small dose of acepromazine makes the pain relievers more effective in smaller doses.

That’s why I like ace. But I don’t tend to reach for acepromazine in the first two instances (for which sedation is the ultimate goal). I happen to believe the side effects related to acepromazine outweigh its benefits in these cases given that plenty of other drugs provide safer, more comfortable alternatives if a quiet animal is your goal. Here’s the down-side of its uses as a tranquilizer/sedative, as presented by Plumb’s Veterinary Drug Handbook (which I urge you all to buy):

  • It reduces the seizure threshold in animals and can bring on seizures in pets predisposed to them (epileptics, brain tumor patients, etc.).
  • At the labeled therapeutic dose indicated for sedation/tranquilization, it can cause profound hypotension (low blood pressure) in some animals.
  • Giant breed dogs and sighthounds can experience extremely deep sedation and prolonged recovery times (indeed, I once saw a greyhound sleep like the dead for two days after half the normal dose was administered intramuscularly)
  • “Acepromazine should be used very cautiously as a restraining agent in aggressive dogs, as it may make the animal more prone to startle and react to noises or other sensory inputs.”
  • In fact, aggressive dogs can sometimes become more aggressive after receiving acepromazine. It's posited that the dysphoria associated with this class of tranquilizing drugs is responsible for this.
  • “Acepromazine has no analgesic effects.” It does not relieve pain. (Though this is not really a down-side unless you’re performing a procedure without other pain relievers on board.)
  • Despite its anti-arrhythmia qualities, it's been observed that boxers can suffer life-threatening arrhythmias with acepromazine––albeit rarely. Veterinarians must always be mindful of this when using ace in boxers. 

Further, Plumb’s goes on to explain that,

“The use of acepromazine as a sedative/tranquilizer in the treatment of adverse behaviors in dogs or cats has largely been supplanted by newer, effective agents, that have fewer adverse effects.


“Its use for sedation during travel is controversial, and many no longer recommend drug therapy for this purpose.”

It’s also believed that acepromazine, used freely for noise phobia, may actually heighten pets’ sensitivity to noise. For this reason, one of my local behaviorists is especially opposed to its use during storm or fireworks season.

All good points. But for me, the larger issue is this: With acepromazine, the potential for dysphoria (an unhappy feeling) is high. Though we have no way of confirming this (except by inference, as in the case of heightened aggression in dogs who receive ace), we do know that similar tranquilizers in humans have fallen out of favor due to their dysphoric effects on people.

Consider Thorazine (chlorpromazine): This drool-on-yourself, One Flew Over the Cuckoo’s Nest kind of tranquilizer was once ubiquitous in human psych wards. Though this acepromazine-like drug is still used, it’s not exactly a kind drug when used in big, human-stopping doses. Still, nothing quiets a raging psychotic like Thorazine does. Same goes for acepromazine in pets. It stops them. And that’s why we like it.

Problem is, not only do we have the case of dysphoria and Thorazine to consider, we also happen to know that acepromazine causes even more profound dysphoria in humans than “Vitamin T” does. That’s why humans very rarely abuse it.

You may abhor the comparison between humans and animals in this case. After all, humans and animals don’t react the same way to all kinds of drugs. Nonetheless, neglecting to use human drug reactions as a starting point for how these drugs might theoretically act in animals seems a silly thing to do. But we do so all the time in cases where psychology is involved. As if animals might not experience similar alterations in brain chemicals in the same way...simply because we can’t ask them how they feel.

Same is true for how pain relief has historically been treated in animals, infants and children. When we can’t measure the psychological effects of pain, we’ve been––until very recently––reluctant to offer chemical relief for it.

Human and animal comparisons aside, I have a problem with acepromazine not only because of the potential for dysphoria, but because it doesn’t address the underlying problem: anxiety. Sure, it keeps staff safe, but all kinds of drugs can do that...while inducing drowsiness and offering the minimized awareness we associate with comfortable sedation in ourselves. Ace, by contrast, doesn’t necessarily achieve this.

Again, if animals are like humans, the tranquilization acepromazine offers allows for continued awareness (perhaps even heightened awareness). In fact, that’s technically the difference between a tranquilizer and a sedative. Tranquilizers, by definition, allow you to retain some awareness.

Then there’s the issue of its "overuse" as a sedative.

Acepromazine is tried and true. We’re comfortable with it. And for some reason, switching from ace to something else––even while all the research tells us it’s safer––is a stressful process for all practitioners. Knowing the ins and outs of how our favorite drug works means more safety in the short run...even though we know better choices are available when it comes to achieving a quiet animal.

That’s why, I believe, acepromazine continues to hold sway in small animal veterinary medicine for sedation. That, its low abuse potential, its relative safety, its effectiveness...and the price factor, of course. Because it’s way cheaper than alternatives like dexmedetomidine and way less “abuse-prone” than hydromorphone (a morphine-like opiate), we tend to stick to it.

But that’s not acceptable as a matter of course say some anesthesiologists and behaviorists. They point out that the very issues that make acepromazine so popular are those that lead to its abuse: grooming and boarding facilities that “ace” everything when things get noisy, veterinary hospitals that hand out ace like pez for every kind of restless pet scenario, veterinarians who ace all aggressive dogs first and ask questions later, etc.

It’s not appropriate to reach for acepromazine in these cases...perhaps not for any kind of scenario in which sedation is the goal, it’s increasingly argued. Not as long as better options are out there that can achieve the same effects more safely and with greater attention to the animal welfare issues involved.

After all, offering ace as a sedative isn't helpful to your pet if her brain doesn’t quiet down along with her body. And it's primarily on this basis that I object to ace: Sedating pets without regard for what they may experience is the height of human hubris. Especially when there's a better way. 

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