Prescribed for Dog - Appetite Question

My dog was prescribed Cipro a few weeks ago for a bladder infection (10 days of treatment, 2 pills per day). About 4-5 days into the treatment, he stopped eating almost entirely. I finally quit giving him the Cipro (his infection has cleared) but it has been about 10 days and he has still not regained his appetite entirely and continues to lose weight. I'm very concerned. He has had an ultrasound, blood work, x-rays, all kinds of tests and they have all come back fine. His vet thinks that the Cipro should all be out of his system by now but my feeling is that the Cipro is still somehow affecting his appetite. Does anyone have any feedback about how to regain his appetite?