Is Metronidazole Safe for Cats?

Metronidazole, sold under the brand name Flagyl, is an antibiotic useful for the treatment of bacterial infections and certain parasitic infections. Metronidazole has a high risk of side effects. Some patients experience nausea or other gastrointestinal discomfort or pain while taking it.

Metronidazole Killed My Cat

“Our 15-year-old cat became lethargic and then stopped eating. Our vet diagnosed a urinary tract infection. She prescribed a dose of metronidazole for 14 days. The first day the cat seemed to perk up, but then became even more lethargic than before and developed diarrhea. He was treated for that but continued to deteriorate until he died four days after starting the metronidazole. I am absolutely certain that this drug killed my cat. The postmortem report said liver failure and possible GI ulcers were the cause of his death. Metronidazole is toxic to the liver at high doses and can cause GI ulcers as well as diarrhea. I am writing this because I had never heard anything bad about this drug before it killed my beloved pet. I had no idea that it could be so dangerous, especially with such a low dose as he was given. Please use extreme caution if your vet prescribes this drug for your pet!”

“My cat was sick for about a week. He was acting lethargic, wasn’t eating or drinking, and had started throwing up. I took him to the vet. They gave him an exam, did some blood work, and sent him home with an antibiotic (metronidazole) that I was supposed to give him twice a day for ten days. The next day he seemed better, so I thought it was working. But then as the days went on, he kept getting worse. He would eat and drink a little bit, but he would throw it all up again within half an hour or so. Then one night I woke up at 3 am because my cat was screaming in agony. He had thrown up a bunch of blood and his stomach hurt really bad. I rushed him to the emergency clinic but they said they couldn’t do anything for him because his vital signs were too unstable. He died a few hours later from gastrointestinal bleeding caused by the medication that was supposed to save his life.”

Will metronidazole hurt a cat?

Metronidazole is a pretty common drug used in cats to treat parasites and infections. It has several side effects, but it can also be toxic to cats. The most common symptoms of Metronidazole toxicity in cats are:

  • nausea
  • vomiting
  • headache
  • loss of appetite
  • diarrhea or constipation
  • dry mouth or increased saliva production
  • darkening of the urine (brown/black color)

The drug can be fatal if a cat is given too much of it or if given for too long. In addition, some cats will have an allergic reaction to it and may develop severe swelling of the face that could cause suffocation.

Metronidazole should never be given to cats with liver disease or blood disorders, or if they are pregnant or nursing kittens. It can also cause neurological damage if taken in high doses or for prolonged periods of time.

Metronidazole is one of the most widely prescribed veterinary drugs out there, but that doesn’t mean you should give it to your pet without being aware of the risks involved. Make sure you talk to your vet about possible interactions between this drug and any other medications your pet takes.

Can cats be allergic to metronidazole?

While metronidazole is a common prescription drug for cats, it’s also common for cats to be allergic to it. In severe cases, just one dose can lead to life-threatening anaphylactic shock.

Many pet owners may not realize the dangers of metronidazole until it’s too late. This is why it’s important for pet owners to know exactly what the symptoms of an allergic reaction are, and what they should do if their cat has an allergic reaction to this medication.

If your cat is allergic to metronidazole, you might notice:

  • rash
  • itching/swelling
  • severe dizziness
  • trouble breathing
  • seizures

How long does it take metronidazole to work in cats?

Metronidazole usually starts working within 1 to 2 hours after you give it to your cat. Metronidazole begins to act quickly in the body, but it takes some time before symptoms will improve.

It should be given orally with food or water to avoid stomach upset unless otherwise directed by your veterinarian.

Positive reviews of metronidazole

“My cats have been on metronidazole for 10 days now and no side effects. The last time they were on it for 7 days and their poop was runny the whole time. I think some people are just more sensitive to the med than others.”

“I do not see anything wrong with giving a cat an antibiotic if he has a bacterial infection but you have to be the judge of that. My vet prescribed it for my cat after he had diarrhea for a week. It worked fine.”

“My cat was on it for at least 10 days without any issue at all – though I did notice her appetite decreased significantly while she was on it, as well as some weight loss (but I assume this was due to poor appetite rather than any effect of the metronidazole).”

“My kitty had to take this medication 3 years ago and the only side effect we saw was drowsiness during the first night. She slept all day and slept most of the night too but by the second day, she was back to her normal self!”

“My cat was diagnosed with gingivitis, and my vet prescribed this, along with a prescription food. After two weeks of use, the condition cleared up completely.”

“This product is amazing! My cat has chronic diarrhea, and the first time she was prescribed this medicine, it worked like a charm. For several months after she was taken off of the medicine, she was fine – no diarrhea at all. However, a few months after that, she started in again with diarrhea. We tried many different foods, supplements, etc., but nothing worked. So we put her back on this medicine and within a couple of days, her diarrhea was gone once again! It seems to be the only thing that works for her chronic diarrhea issues.”


Hannah Elizabeth is an English animal behavior author, having written for several online publications. With a degree in Animal Behaviour and over a decade of practical animal husbandry experience, Hannah's articles cover everything from pet care to wildlife conservation. When she isn't creating content for blog posts, Hannah enjoys long walks with her Rottweiler cross Senna, reading fantasy novels and breeding aquarium shrimp.

One Response

  1. I think Flagyl killed my older cat. She was originally prescribed Synulox for gingivitis which was difficult to administer but seemed to work. After 7 days I suspected the infection might still be there as there was a little mouth odor and had telephone contact with the vet. I found him rather brusque when I asked what to do, he just said he’d give me another batch. But it turns out the second batch was Flagyl. After using this my cat couldn’t walk or even stand properly, lost her appetite and significant weight and a week or so later died from massive internal bleeding.

    I wasn’t told about any of the side effects or to watch out for anything. It was given to me by one of the assistants. More than it just being the drugs this was down to a lack of information. My cat was older and already walked with a little more difficulty, but nothing like this. This drug plus lack of care and information is lethal.

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