My dog was on metronidazole last year for colitis. The vet put her on two meds. I don't remember the other off hand but another vet was surprised she was put on both at the same time. She also was given a higher dose than my other dog who is a bit bigger than her. She became incontinent. After searching the internet I found this was a side effect. It took a while but it finally passed. I believe it was the medicine and it had to completely leave her system for her to get back to normal.
our dog was was put on a long term dose of metronidazole for irritable bowel syndrome a few months ago. unfortunately the medicine caused severe neurological issues in our 12 year old lab/husky. shortly after taking his morning dose one day, he wasn't able to walk straight and lost all control of his limbs. he's mostly recovered, but i think he has had some side effects from this medicine. he was experiencing some arthritis issues prior to this but it's gone down hill rapidly since (the neurological episode occurred this past june, and now our pup can't nearly walk as far as before, despite herbal treatments and acupuncture). i think the use of a long term dose of metronidazole should really be studied further.