Metronidazole Side Effects in Dogs

Metronidazole is the active ingredient in several brand name drugs, including Flagyl, Metizol, Metrogel, MetroCream and Protostat. It is given to dogs to clear up bacterial infections in the digestive system such as giardia or entamoeba. It's also used to help prevent infection when dogs need surgery done on their bowels. It comes in gel, pill and intravenous forms.

  1. Time Frame

    • Side effects usually do not begin in a dog for 7-12 days after they have their first doses of metronidazole, Dr. Kate A.W. Roby writes in "The Pill Book Guide to Medication For Your Dog and Cat." Only adult dogs should be given metronidazole as it can cause defects in growing puppies. It can be passed through breast milk, so nursing dogs should not receive metronidazole, either.

    Common

    • The most common side effects from metronidazole are the dogs reacting to the medication's bad taste. This can include gagging, drooling excessively, pawing at the mouth or rubbing the sides of the mouth on the floor. Other common side effects are nausea (shown when a dog lips its lips a lot), vomiting and loss of appetite.

    Rare

    • Rare side effects include watery diarrhea, depression, lack of energy, blood in the stool, blood in the urine or a noticeable darkening of urine color. The lack of energy and depression can be from a low white blood cell count, which is thought to be caused by metronidazole. The rarest side effect is sudden liver failure.

    Overdose

    • The symptoms of an overdose include sudden coordination problems such as walking with a stagger, total disinterest in food, persistent vomiting instead of just vomiting once, involuntary eye movements, lethargy and seizures, according to Dr. Dawn Ruben. She also notes that dogs most susceptible to overdoses are those with liver problems. Call a vet immediately if these symptoms occur.

    Long Term

    • Metronidazole is usually not given more than two weeks to reduce the chance of long-term side effects. The drug has been known to stress the liver and kidneys of dogs and cats. Dogs that already have liver or kidney problems need reduced doses of metronidazole. There is a slight possibility that metronidazole can cause liver damage in healthy dogs.