Hi, I am Dr. Jeff. I will try to help you. Please feel free to follow up if any more information is needed. The good news is that Xanax is used in veterinary medicine for the treatment of anxiety and stress. The high end dose is 0.05 mg/lb twice daily. This makes the high end dose 0.85 mg. So, I would not expect an issue tonight. Things should be fine. I hope this helps and gives you peace of mind.