Poor guy, I'm sorry he is so stressed! Behavior cases can be tricky and it takes patience to find the right combo to help him, especially when things are being destroyed. You have to be careful mixing Alprazolam with Acepromazine, you can see one of two outcomes. They typically work synergistically together, so you use lower doses of each when combined. I have also seen dogs have a paradoxical reaction to both, meaning instead of decreasing anxiety, they are worse and very hyper-excitable. Is it possible this happened with the 75 mg ace dose?
Since Alprazolam is a controlled substance and I have not performed an exam on him, I cannot, by law, give you a recommendation on using it. You are pretty much maxed out on the Acepromazine dose. If you elect to try the Alprazolam, just watch for marked sedation.
If lab work has not been done, I would still recommend it to make sure there are no underlying endocrine causes for the anxiety. I would also encourage finding a behaviorist near you for a more thorough work up and the ability to discuss behavior modification and desensitization to the source of his anxiety (most likely separation anxiety given breed, they are really attached to their people!).
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