As with many antibiotics for cats, dogs, and horses, some side effects may occur. When using Metronidazole for dogs and cats, watch for neurologastro-intestinal disorder, lethargy, weakness, neutropenias, hepatoxicity, hematuria, anorexia, nausea, vomiting, and diarrhea. Though not common, serious side effects may occur, such as low white blood cell count, liver failure, and blood in the urine, or dark urine. Long-term use or overdose may cause neurologic symptoms as well. Metronidazole has also been known to cause birth defects, and should not be used by pregnant mothers.
Some medications and antibiotics will interact with Metronidazole for dogs and cats. Do not combine with any of the following medications: Cimetidine (Tagamet), Phenytoin (Dilantin), Phenobarbital, or Warfarin (Coumadin). Other drugs may also affect Metronidazole for dogs and cats, so be sure to consult your veterinarian before starting this medication.