What Is Metronidazole for Cats?
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).
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
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
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.
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.
Caution is recommended with the use of metronidazole in the first third of pregnancy due to the risk of foetal abnormalities.
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.