My lil boy is on metronidazole. Long term therapy for IBD. We've never had any problems. Of course I'd prefer him not on any Meds, but it keeps his tummy trouble under control. We are now able to go longer between doses. He was on it daily. Now I only have to use it during flare ups. He's on prednisone also. We have been able to cut way back on that as well. Each pup is different, but my experience with metro has been positive.