You're speaking to Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply.
Bernard, I'm sorry that your question wasn't answered in a timely manner and I regret to tell you that we're not allowed to prescribe through this venue. I suggest that you ask his vet to send home a tranquilizer such as acepromazine that you would administer 2 hours prior to arriving at the vet hospital. The tranquilizer might be enough for the vet to work on your Rottie or, at least, less of a dissociative ("spacer outer") or anesthetic needed to be given to him.