My vet prescribed Metrogyl / Flagyl / Metronidazole.   What does that mean?

Metronidazole is an antibiotic and antiprotozoal drug, sold in Australia under the brand names Metrogyl and Flagyl, as well as under the drug name Metronidazole.  The different brands offer the same active ingredient in different strengths and different delivery methods (tablet, suspension, paste etc) and you should check with your vet if you intend to change between the brands.


Metrogyl for dogs and cats is generally used to stop diarrhea or loose stools.  It works well against certain infections like giardia and trichomonasis, as well as anaerobic bacteria.  Metrogyl and Flagyl are also used in dogs and cats to relieve inflammation of the intestinal tract, and sometimes for infections in bones, teeth (including peridontal disease) and the central nervous system.


Metronidazole is also sold as a paste to treat bacterial infections in horses.


This article answers some of your common questions, such as how Metrogyl helps your pet, the dosage for metronidazole, and the side-effects of Flagyl or Metrogyl for pets.

Metrogyl and infections & parasites?

Metronidazole (as either Metrogyl or Flagyl) is often prescribed when your pet has a bacterial infection, or certain internal parasites (particularly those that exist in un-oxygenated (anearobic) environments).  These infections or parasites may have given your pet diarrhea. 

What is Metronidazole (Metrogyl or Flagyl)?

Metronidazole is both the brand name for the drug, and the name of the active ingredient  - other brands that have metronidazole as their active ingredient are Metrogyl and Flagyl.


Metronidazole is an antibiotic that belongs to a group of medicines called nitroimidazoles.  Metronidazole works by destroying the DNA of the infecting organisms, killing or stopping the growth of the bacteria or other organism causing infection.  It is particularly useful because it can penetrate the blood-brain barrier, and the bone barrier, meaning it is used to treat organisms affecting the central nervous system or teeth or bones.   

What can I expect when my cat or dog starts on Metronidazole?

  • Metrogyl/Flagyl should take effect within 1 to 2 hours.  Although its effects may not be noticed immediately, you should see gradual improvements after a few days.
  • Metronidazole is an antibiotic, and just like when you take an antibiotic, it is important that your pet takes the full course of antibiotics, for the length of time that your vet has prescribed the drug for your cat or dog, to prevent reinfection.
  • It is important that you periodically discuss your pet’s response to Metronidazole with your vet, who will determine if your cat or dog is responding as expected, and what the length of the course of Metronidazole should be.  

How to give Metronidazole to my pet?

Metrogyl is available as a tablet, and Flagyl is available as a tablet or a suspension - your vet will discuss with you the appropriate dosage and form of metronidazole for your pet. Metronidazole can be very bitter to taste, and if you have troubles getting your pet to take the dosage, talk with your vet.  


In both suspension and tablet form, metrogyl or flagyl are given with food. Flagyl suspension should be well-shaken in the bottle before measuring out the dose.


Metronidazole paste is prescribed for horses, and you should follow your vet’s instructions.


Possible side-effects of Metronidazole

Metronidazole is very safe.  The most common side effect is a reaction to the bitter taste, or gastrointestinal upsets.  Sometimes, it can cause nausea, vomiting, decreased appetite or excessive salivation.  As with any medication, if you are concerned about a possible side effect of Metronidazole, stop treatment and contact your vet immediately.  In particular, call your vet if you suspect:

  • Allergic reactions or anaphylaxis: Swelling, difficulty breathing, throat closing, or hives. Animals experiencing a severe allergic reaction need immediate medical care. 
  • Neurological problems: Seizures, staggering, stiffness, strange movements, or behavior.

Storage of Metronidazole

The manufacturer of Metronidazole recommends that tablets be stored at room temperature (below 25 degrees).

Who should NOT take Metronidazole?

  • If your pet is taking blood thinners, or has a liver or kidney disorder 
  • Metronidazole shouldn’t be used by kittens or puppies, breeding, pregnant or lactating animals, as it may cause birth defects and is excreted in breast milk.
  • Some drugs don’t work as well, if your pet is also taking Metronidazole, and there are drugs that cannot be taken with Metronidazole.  For this reason, please make sure that you tell your vet about all other medications that your pet is taking, including vitamins, supplements and herbal therapies.   

What if I give too much Metrogyl/Flagyl/Metronidazole? What if I miss a dose of Metrogyl or give the wrong dose of Metrogyl?
Administration of drug issues

If you miss giving a dose of Metrogyl, don’t worry.  If you remember a missed dose, give the dose as soon as possible. However, if it is close to the time that the next dose is due, skip the missed dose, and continue with the regular schedule. Never give your pet two doses at once.

Can I buy Metrogyl or Flagyl or Metronidazole online?

Metronidazole, under any brand name, is a prescription medicine, and you can buy it online from PetScripts once you have a script (prescription) from your vet.  Please ensure that you have read the How to Order page before ordering this item.


This information is not intended nor is it implied to be a substitute for professional medical or veterinary advice or any information contained on or in any product packaging or labels. Always seek the advice of your Veterinarian, Pharmacist, or qualified health provider when starting any new medical treatment, continuing with medical treatment or with any questions you may have regarding your animal's medical condition. Professional advice is required for each particular illness, disease, infection, injury or other medical condition and for dosages of the pharmaceutical product supplied via this website. You take full and total responsibility for what you do with this information and any resulting outcomes from your actions.