Metronidazole and Your Dog

The following are real life questions about Metronidazole use in Dogs that have been treated by Dr. Mike Richards, DVM.

Problems with Metronidazole Long Term
Metronidazole and Possible Liver Damage
Metronidazole - Flagyl
Metronidazole and Cancer

Problems with Metronidazole Long Term

Question:

Could the frequent use of Metronidazol (for Giardia) be as 'hazardous' as the use of Pred., for causing Cushing's- like symptoms? There are numerous symptoms that indicate the possibility of Cushing's -- how many of them do you believe a dog should have, before it's reasonable to test for it? I.e., if a breed (that is uncharactistic of having Cushing's) does not eat, drink, or urinate excessively, but is experiencing some hair loss and skin thinning (at a Sr. age), would you test for Cushing's?

Answer:

I have not seen Cushing's like syndromes using metronidazole. The only long term problem that I know of with metronidazole use is that it is thought to be carcinogenic in some lab animals and possibly in humans, with long term use. This has not been proven to occur in pets but it might be a problem.

I usually don't test for Cushing's disease unless clinical symptoms are occurring that have to be corrected in order to make the patient comfortable or unless the client asks me to, prior to that time when we include it in a list of possible differentials. I would probably test if there was bilateral hair loss and other hormonal diseases, especially hypothyroidism, have been ruled out.

Read our overview of Metronidazole for Dogs.

Question:

Have you ever heard of Flagyl affecting the liver enzyme levels?

Answer:

Metronidazole (Flagyl Rx) is metabolized primarily by the liver. It sometimes causes liver damage or makes existing liver damage worse. This is thought to be a reversible effect which usually will resolve with withdrawal of the medication. 

Learn more about Flagyl - the name brand version of Metronidazole.

Question: 

Have you anything to offer about Flagyl - pros/cons, dangers, etc? This is what I heard.." It is a type of antibiotic that is used commonly in dogs with gastric problems. I am very leery of it, as I had a very dear girlfriend die from using this about 20 years ago. It is also called antiabuse, and used for alcoholics, as it makes them nauseated when they drink... it puts a big toll on the liver, and can cause liver shut down and failure."

Answer: 

The first thing that is necessary is to clear up a misunderstanding in the email responses what you heard. Antibuse (Rx) is disulfiram, not metronidazole. However, metronidazole can cause vomiting when given with alcohol, in a reaction that has been termed "disulfiram like" in the human literature, so perhaps that is the reason for the confusion.

Metronidazole has never been approved for use in dogs and cats but it is used quite frequently to treat giardiasis and inflammatory bowel disorders. It is also used to aid in the treatment of anerobic bacteria in the respiratory tract.

Metronidazole can cause neurologic signs if overdosed, including loss of balance, visual problems, vomiting, rapid eye movements (nystagmus), tremors and seizures. I have only seen this problem once or twice, when we have tried to use metronidazole in young kittens to treat giardia and could not get the dosage measured accurately using crushed pills. The kittens didn't die, but they looked like they might. Now we use a compounding pharmacy to make the medication into a dosage form we can give accurately. Metronidazole is processed by the liver and may cause increased toxicity if given to a patient with enough liver disease to inhibit processing of the medication.

If you need more specific information about any part of the above reply I will try to find it for you. Our biggest problem with metronidazole has been vomiting after administration, making it an unpleasant medication for the pet and often ineffective when that occurs, too.

Question:

The second question is do you know what the clinical trials indicate as far as the association of cancer and the use of metronidazole. Thank you for your help.

Answer:

I am not aware of any studies linking metronidazole to cancer. It is known to be teratogenic (causes birth defects) when administered to lab animals who are pregnant but I don't know if this occurs in dogs and cats. I have no intention of giving it to a pregnant pet, though. It can also cause neurologic signs in some pets even at the recommended dosages. These go away when the medication is withdrawn (or at least they have in the few cases we have seen). Mike Richards, DVM