I am not a vet, so I only know about the humans - but clomipramine works fairly quickly, maybe not as fast as Xanax. With comipramine in humans we always have to watch for weight gain, diabetes, and drowsiness. Xanax is not known to cause the weight gain and drowsiness, however, Xanax is a benzodiazepine and therefore addictive and cannot be stopped quickly if they have have been on it a long time (however, not got to stop anything someone has been on a long time). Most of these issues have a lot to do with dosage and such.
When Cali was attacked by the hawk several years ago she was quite anxious - kept looking for something to come at her from above - I used low dose Xanax for about a year and a half while we worked through it, and weaned her off slowly and we did just great! Liquid Xanax is very fast acting and easy to give, but expensive, the pill is much cheaper but Cali liked the bubblegum flavor with the liquid
. Some pet folks keep it around for 4th of July and New Years Eve scare for their dogs - and storms. Seems I hear most use Acepromazine for storms, but that may be vet preference.
Xanax can be used intermittently better than clomipramine in my opinion but many folks do use it intermittently successfully.
Good luck! We so hate to see our pups miserable.