Metronidazole for Dogs and Cats
FatCamera/E+/ via Getty Images
PetMD’s medications content was written and reviewed by veterinary professionals to answer your most common questions about how medications function, their side effects, and what species they are prescribed for. This content shouldn’t take the place of advice by your vet.
What Is Metronidazole Used for Dogs and Cats?
Metronidazole is an antibiotic and antiprotozoal prescription medication that kills certain types of bacteria and protozoa parasites.
In dogs and cats, it is most used to treat infections and inflammation in the digestive tract. It also treats protozoal parasites, such as Giardia, especially when given in combination with other medications.
Metronidazole is most frequently given as an oral medication and is also available as an injection administered in the hospital by a veterinarian. Your veterinarian will determine which combination is best for your pet, based on their circumstances and symptoms.
Is Metronidazole FDA-Approved?
Available in a flavored oral liquid (suspension) formula, Ayradia (active ingredient metronidazole) is the first FDA-approved animal medication for the treatment of Giardia duodenalis infection in dogs and puppies.
Metronidazole, on the other hand, is FDA-approved for human use under the brand name Flagyl® and as generic metronidazole.
Metronidazole is currently not FDA-approved for use in other animals. However, it is readily utilized in the veterinary field, and veterinarians can legally prescribe certain human drugs for use in animals in certain circumstances, such as in cats. This is called extra-label or off-label use because this use is not described on the drug label.
Speak with your veterinarian about whether metronidazole is right for your pet.
Compounded Metronidazole
In certain circumstances, your vet may recommend a compounded formulation of metronidazole.
Compounded medications are prescribed if there’s a specific reason your pet’s health can’t be managed by an FDA-approved drug, such as if your pet has trouble taking pills in capsule form, the dosage strength is not commercially available, or the pet is allergic to an ingredient in the FDA-approved medication.
Compounded medications are not FDA-approved. They are created by either a veterinarian or a licensed pharmacist on an individual basis to best suit a patient’s particular needs.
Metronidazole Considerations for Dogs and Cats
Metronidazole should not be used in animals who are sensitive to the medication or other medications categorized in the same antiprotozoal drug class, such as ronidazole.
Metronidazole should be used with extreme caution in animals who are extremely ill, pregnant, or nursing, or in animals with decreased liver function.
Always discuss your pet’s medical conditions and medications, including vitamins and supplements, with your veterinarian first before giving metronidazole, as there may be health risks to your pet if they are taking certain other medications.
How Metronidazole Works in Dogs and Cats
Metronidazole kills bacteria by disrupting their DNA. It is not fully understood how metronidazole and other medications in its 5-nitroimidazole drug class kill protozoa, but it is thought that they generate free radicals that disrupt the DNA of the protozoa.
Metronidazole is also used to treat inflammatory diseases in the digestive tract, and is thought to accomplish this by blocking certain inflammatory mechanisms.
How To Give Metronidazole to Dogs and Cats
Follow the directions on the drug label or as provided by your veterinarian.
For metronidazole:
-
The exact dose of metronidazole depends on your pet’s weight, as well as the type of bacteria or parasite present.
-
Metronidazole should be given for the full treatment period prescribed by your veterinarian.
-
This medication should not be given to breeding, pregnant, or nursing dogs because it may cause birth defects, as the medication is secreted into breast milk.
-
Metronidazole should not be used in animals that are sensitive to it or other medications in its 5-nitroimidazole drug class.
For Ayradia:
-
Ayradia can be given with a small amount of food or directly into your dog’s mouth. Giving it with food can decrease the risk of digestive upset.
-
At the time of this article’s publication, studies had not been performed to evaluate the safety and effectiveness of Ayradia in breeding, pregnant, or nursing dogs.
Missed a Dose?
Speak with your veterinarian about what to do if you forget to give a dose of metronidazole.
Generally, your vet may instruct you to give it when you remember, or if it is almost time for your pet’s next dose, to skip the missed dose and resume your normal dosing schedule. Do not give extra or double doses.
Possible Side Effects of Metronidazole in Dogs and Cats
Metronidazole is generally well-tolerated in both dogs and cats.
Cats did not show side effects in dosage and safety studies.
Side effects in dogs may include:
-
Behavior changes, including fatigue (lethargy) or hyperactivity
-
Abdominal pain
-
Weakness
-
Low white blood cell counts
-
Neurologic symptoms, including lack of coordination, dilated pupils, abnormal eye movements called nystagmus, or seizures
Neurologic side effects are more common in dogs and cats receiving higher doses or who are on this medication for long periods of time.
Human Side Effects
Due to possible side effects, humans should never use medicine dispensed for their pets and pets should not be given any medicine dispensed for a human’s use. Flagyl and generic metronidazole tablets frequently have dosages different from those prescribed for your pet by a veterinarian.
Pregnant women or individuals allergic to metronidazole should wear gloves when handling the medication and wash their hands after use.
If you accidentally ingest a pet medication, seek medical attention in person or call Poison Control at 800-222-1222.
Other side effects to consider regarding Ayradia, specifically, include:
-
Ayradia (metronidazole oral suspension) is a prescription veterinary medication not intended for use in people.
-
People who are sensitive to metronidazole should avoid contact with Ayradia.
-
Ayradia is a skin sensitizer that can potentially cause allergic contact dermatitis.
-
Wash hands after use and avoid contact with skin. In case of skin contact, wash the affected area thoroughly. People who come into contact with their dog’s saliva during the first five minutes of administration should also wash their hands.
-
If Ayradia has been added to your dog’s food, the food should be kept away from children until after your dog has finished eating.
Monitoring Your Pet
No specific monitoring is required for this medication, but your veterinarian may recommend routine testing depending on your pets' individual needs, other medications they may be prescribed, and/or the issue that initially caused your pet to be placed on this medication.
When To Call Your Vet
Call your veterinarian if you see any of the following:
-
Severe side effects (above)
-
Your pet’s condition worsens or does not improve with treatment
-
You see or suspect an overdose
-
If you have additional questions or concerns about the use of metronidazole or Ayradia
Metronidazole Overdose Concerns in Dogs and Cats
Overdoses of metronidazole in dogs can cause:
-
Life-threatening neurologic symptoms such as seizures
Overdoses in dogs often require emergency treatment to limit the absorption of the medication and minimize neurologic symptoms.
Metronidazole overdoses given long-term (several months in a row) to cats can cause neurological symptoms.
If you suspect an overdose, immediately seek emergency veterinary care or contact an animal poison control center. Consultation fees often apply.
-
Pet Poison Helpline 855-764-7661
-
ASPCA Animal Poison Control 888-426-4435
How To Store Metronidazole for Dogs and Cats
Keep the following storage tips in mind for this medication:
-
Ayradia (metronidazole oral suspension) should be stored in the upright position below 86 F (30 C) and does not need to be refrigerated. Once opened, use within six months.
-
Metronidazole tablets should be stored at controlled temperatures of 59–77 F (15–25 C).
-
Keep the container tightly closed to protect it from moisture and light.
-
Compounded medications should be stored according to the compounding pharmacy’s label.
-
Keep out of reach of children and pets.
-
Always confirm storage requirements by reviewing the label.
Metronidazole for Dogs and Cats FAQs
How long does metronidazole take to work?
Metronidazole begins working within a few hours of your pet taking it, but it may take up to a few days for your pet’s digestive symptoms to improve, depending on their underlying medical condition and individual health status.
What is the most common side effect of metronidazole?
The most common side effect of metronidazole in dogs is digestive upset, such as vomiting or diarrhea. Cats tolerate metronidazole very well and typically do not have side effects.
What parasites does metronidazole treat?
Metronidazole (active ingredient in Ayradia) treats a protozoan parasite called Giardia duodenalis.
No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer.