Acepromazine or ACE is one of the most commonly used tranquilizers in veterinary medicine. It can cause hypotension (lowering of blood pressure). This effect may be exaggerated in Boxers and there have been many reports of death in Boxers after the use of acepromazine. Consider asking your vet not to use this on your boxer for any reason. More Info here.
Boxers are prone to have bad hearts. SAS and cardiomyopathy checks needed on breeding animals to help control this. For more reading on the subject, Boxer Cardiomyopathy by Dr. Wendy Wallner, DVM
Possible thyroid problems check. A note for all boxer owners. First let me say I'm by no means a vet and the following is my personal feelings. If you own a boxer over a year old please consider having a T4 test for thyroid levels done. Low thyroid in boxers is not uncommon and it's rarely fatal but it can affect the quality of life if not detected and treated. Weight problems, thinning hair, and dark patches on the flanks are just a few of the possible symptoms. Low as well as low normal results should be treated most often with Soloxine ranging from 0.3 to 0.6 and always twice a day. For more info check here and click on Your Dog and the Thyroid