Acepromazine or Acetylpromazine (More commonly known as ACP or Ace it is a psychotropic drugs, used little in humans, however frequently in animals as a sedative and antiemetic. Its principal value is in quietening and calming frightened and aggressive animals. The standard pharmaceutical preparation, acepromazine maleate, is used extensively in equine, feline, and canine; especially as a pre-anesthetic agent often in conjunction with Atropine, and often an opiate such as morphine or buprenorphine.
So, when talking to the vet I would just ask. "Do you use Ace to sedate animals" If they say yes then ask, do you also use it in Boxers. If they say yes then they dont know much about Boxers.

The answer should probably be "Yes we do but not in Boxers"