Metronidazole Side Effects for Cats


Metronidazole, also prescribed under the brand name Flagyl, is an oral medication commonly given to cats to treat both bacterial and protozoal infections, most of which can cause diarrhea. While this medication typically has minor side effects, it sometimes can cause serious neurological symptoms and allergic reactions that can be deadly. The most serious side effects occur with prolonged use or if your cat is given very high doses of metronidazole.

Typical Side Effects

  • The most common side effects in cats taking metronidazole include vomiting, diarrhea, loss of appetite, dark or bloody urine, lethargy and weakness, according to the Doctors Foster and Smith website. After administering the medication, your cat may drool, paw at her mouth, gag or even vomit because this medication tastes unpleasant to our feline friends. Let your vet know if you see any of these side effects, which may take a few days to occur. Your vet may need to examine your kitty to determine if these side effects are serious enough for her to stop taking the medication.

Toxic Side Effects

  • In rare cases, metronidazole can cause toxicity and lead to neurological problems in cats that are potentially fatal. Signs of toxicity include stumbling, disorientation, tremors, stiffness, head tilting and seizures. Your kitty's eyes may shift back and forth rapidly as well. In some cases, nerve damage can occur, resulting in your cat knuckling over on her paws or having trouble walking. Metronidazole also can cause liver disease, which may result in yellowing of your cat's skin, gums and eyes. Get your cat to the vet immediately if you notice any of these side effects, as they can be dangerous if not treated quickly. Unfortunately, the reason why metronidazole can cause neurological side effects is unknown, according to the VetContact website.

Allergic Reactions

  • Some cats may experience an allergic reaction when taking metronidazole. Symptoms of such a reaction include swelling of the face, itchy skin, hives, seizures, pale gums or even coma. After taking the medication, your kitty might experience sudden vomiting or diarrhea. She also might go into shock. Monitor your feline friend after she takes her veterinarian-recommended dose of the medication. If you notice any of these side effects, she could be allergic to the medication. Notify your vet immediately. Your vet may put her on another type of medication to avoid these types of reactions.

Drug Interactions and Concerns

  • Giving your feline friend metronidazole along with the drug cimetidine can increase the chances of harmful side effects. Phenobarbital, typically prescribed to treat epilepsy in pets, may decrease the effectiveness of metronidazole. Consult with your vet if your cat is taking any other medications before administering metronidazole to her, especially any sedatives, anticoagulants and phenytoin, which can negatively interact with this medicine, according to PetMD. Metronidazole is not appropriate for pregnant or nursing cats or young kittens. Because of the way metronidazole is metabolized, ask your vet if it is appropriate for use in your cat if she suffers from liver or kidney issues.

Resolution of Side Effects

  • If your kitty experiences any negative side effects from taking metronidazole, it may take one to two weeks for them to go away after you stop the drug. Your feline friend may require supportive care from your vet during this time to help alleviate her symptoms until the metronidazole is out of her system.

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