Metronidazole For Cats: Uses, Dosage & Side Effects

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Metronidazole for cats feature

Metronidazole (most common brand name is “Flagyl”) is an antibacterial and antiprotozoal medication that’s approved for use in dogs and cats in some countries (eg UK and Australia), and is used “off label” for dogs and cats in other countries (e.g. USA).

Metronidazole For Cats Overview

Medication Type:
Antibiotic, Antiprotozoal
Form:
Capsule, Tablet, Liquid
Prescription Required?:
Yes
FDA Approved?:
No
Brand Names:
Flagyl, Flagyl ER, Flagyl IV RTU, Metizol, Protostat, Metrogel
Common Names:
Metronidazole

It belongs to a group of antibiotics known as nitroimidazoles. Metronidazole was first used in France in 1960 and is now used widely around the world.

How Metronidazole Works

The drug has an antibacterial and anti-protozoal effect. In bacteria, under anaerobic (zero oxygen) conditions, metronidazole changes into constituents that bind to DNA, causing cell death. Its mechanism of action against protozoa remains unknown.

Metronidazole is particularly effective against anaerobic bacterial infections (anaerobic bacteria multiply in the absence of oxygen). Resistance to this antibiotic is rare, it’s inexpensive, it has good tissue penetration, and it produces relatively mild side effects at standard doses. This is the drug of choice for many anaerobic and protozoal infections, with its bitter taste being a restricting factor in cats (see below).

Metronidazole also has anti-inflammatory effects by modulating cell-mediated immune responses making it helpful as an adjunct for the treatment of some cases of inflammatory bowel disease and colitis.

Metronidazole is absorbed effectively from the gastrointestinal tract, achieving widespread tissue penetration around the body including bone and central nervous system. It is often selected as an adjunct to other antibiotics because of its effect on anaerobic infections.

Metronidazole may also be given intravenously, as an injectable solution.

Uses Of Metronidazole For Cats

How Metronidazole is Used

Metronidazole is used to treat bacterial and protozoal infections, as well as hepatic encephalopathy.

As well as being used to treat susceptible bacterial (e.g. in periodontal disease, where anaerobic bacterial infections are a particular concern) and protozoal infections (e.g. Giardia), metronidazole may be used to assist the treatment of hepatic encephalopathy in cats.

The main restricting factor in the use of metronidazole for cats is that they find the taste of the antibiotic bitter and unpalatable, making it be difficult to give oral medication.

In some countries (e.g. USA), a compounding pharmacy may formulate the medication in special gelatin capsules that can be directly administered to cats for this reason.

Metronidazole used to be used, along with fenbendazole, to treat the protozoal infection, Trichomonas, but these days, more modern medication is likely to be recommended.

How It’s Administered

Three formulations of metronidazole are generally available.

  • Metronidazole Intravenous Injection – Metronidazole is available as a 5mg/ml solution designed for intravenous infusion.
  • Metronidazole Tablets – Metronidazole tablets are film-coated and come in a range of sizes from 200mg upwards. Given that the maximum dose for cats is likely to be less than 100mg, the large tablets are unlikely to be used.
  • Metronidazole Oral Suspension – An oral suspension containing 40 mg/ml metronidazole is available.

What Is The Dose Rate Of Metronidazole In Cats?

The recommended dose rate is usually 10 mg/kg twice daily, orally or intravenously, but in some cases, doses as high as 25mg/kg may be recommended.

For a 5kg cat, 10mg/kg equates to 50mg (a quarter of a 200mg tablet, or 1.25ml of oral suspension).

Side Effects Of Metronidazole For Cats

Side effects of metronidazole for cats

There are several side effects associated with metronidazole for cats. Due to the medication’s bitter taste, salivation is the most common side effect. Other adverse effects may occur, but they are rare.

Other than excessive salivation due to the bitter taste, side effects at standard dosing rates are uncommon in cats. Adverse effects such as loss of appetite, nausea, and gastrointestinal effects such as vomiting may rarely be seen. As with all drugs, allergic reactions are a possibility.

Metronidazole toxicity may be seen at high doses (e.g. over 25mg/kg twice daily). Signs include vomiting, neurologic signs due to central nervous toxicity (nystagmus, ataxia, disorientation, knuckling, head tilt, and seizures), as well as liver disease and blood in the urine.

This toxicity is more likely after prolonged therapy, or in animals with liver disease (the drug is metabolised by the liver). If such signs are seen, the drug will be withdrawn, and general supportive treatment will be given.

Drug Interactions

If given at the same time as cimetidine, there may be reduced clearance of metronidazole, increasing the risk of toxicity. Co-administration with cyclosporine may also increase the risk of toxicity.

If given at the same time as barbiturates (such as phenobarbital), phenytoin, or anticoagulants (e.g. warfarin), there may be increased clearance of metronidazole, so higher dose ranges may be suggested by your DVM veterinarian.

Risk Factors

Caution is recommended with the use of metronidazole in the first third of pregnancy due to the risk of foetal abnormalities.

In Conclusion

Metronidazole is a useful antibacterial and antiprotozoal drug in the veterinary medicine armoury. It should always be used under close veterinary control, as a prescription-only medication.

Frequently Asked Questions:

What is metronidazole used for in cats?

This antibacterial and antiprotozoal drug is used under veterinary control to treat susceptible infections, and it may have some use as an anti-inflammatory for some cases of inflammatory bowel disease (IBD).

Does metronidazole make cats tired?

As mentioned, metronidazole toxicity can cause central nervous signs, that can include dullness, so if your cat seems tired when on this medication, you need to discuss this with your veterinarian.

How long can a cat take metronidazole?

Duration of treatment is a decision for your veterinarian, as this is a prescription-only medication. Sometimes, in some situations, long term use may be recommended, but note that this may increase the risk of adverse side effects/toxicity.

How much metronidazole do I give my cat?

This is a decision for your veterinarian, but generally the dose rates recommended above will be used.

About Dr. Pete Wedderburn, DVM

Dr Pete Wedderburn qualified as a vet from Edinburgh in 1985 and has run his own 4-veterinarian companion animal practice in County Wicklow, Ireland, since 1991. Pete is well known as a media veterinarian with regular national tv, radio and newspaper slots, including a weekly column in the Daily Telegraph since 2007. Pete is known as "Pete the Vet" on his busy Facebook, Instagram and Twitter pages, regularly posting information on topical subjects and real-life cases from his clinic. He also write a regular blog at www.petethevet.com. His latest book: “Pet Subjects”, was published by Aurum Press in 2017.

7 thoughts on “Metronidazole For Cats: Uses, Dosage & Side Effects

  1. Sue

    Metrogel is listed in the brand names. Can metrogel be used as a transdermal for cats to get rid of giardia.

    Reply
  2. Ethan S

    Be careful. It appears our 3-month old kitten is suffering metronidazole toxicosis. She had horrible seizures yesterday and had to be hospitalized. She needed diazaprem to stop the seizures. Right now she is resting at he vet. We are praying she recovers. Our kitten was on metroninidozale for 1 week.

    Reply
  3. Linda J

    I took my ill kitty to an emergency animal hospital. They weighed her and said she weighed 12.5 lbs, which is less than 6 kg. After an extensive exam, they didn’t find anything to explain her diarrhea and weight loss but prescribed 62.5 mg of Metronidazole, twice a day for 14 days. That’s 120 mg per day which sounded like a lot for a small cat. They gave her the first dose at the clinic and by the time we got home (45 min. away) she was lethargic, her eyes rolled back in her head, she couldn’t hold her head up, she couldn’t stand up and her pupils were dilated. I called them and the veterinarian who treated her said Metronidazole doesn’t do that to cats. Maybe it doesn’t if you don’t overdose them. That vet said I could cut the dosage in half but I didn’t give it to my girl again. Well the problem isn’t resolved and the usual vet wants to give her Metronidazole again. You can bet we will have a really long discussion before I dose her again. Maximum is 7.5 to 10 mg per kg from what I read on multiple vet sites and the drug manufacturer’s site. The cat now weighs less than 5 kg and I will be very wary of just doing what a vet says without checking it out myself. Just like I am with my own medications.

    Reply

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