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Medication details

  • Medication type: Antibiotic, Antiprotozoal
  • Form: Liquid, Tablet, Injection
  • Prescription required? Yes
  • FDA approved? No
  • Life stage: All
  • Brand names: Flagyl
  • Available dosages: 250 mg tablets, 500 mg tablets
  • Expiration range: 3 years

No one likes dealing with dog diarrhea. But if you’ve encountered this stinky situation, your veterinarian may have prescribed a drug called metronidazole for your pup. 

Metronidazole is commonly used to treat conditions like acute onset diarrhea, inflammatory bowel disease, giardia, and other diseases of the gastrointestinal (GI) tract, liver, and soft tissues. 

Most dogs tolerate metronidazole well, but there are some things you should know about this medication before giving it to your dog. Read on to learn more about metronidazole and its myriad uses in veterinary medicine!

What is Metronidazole?

Dog looking confused and looking at camera

Metronidazole, also known by the brand name Flagyl, is an antibiotic medication commonly used in both human and veterinary medicine. In humans, metronidazole is FDA approved in several different forms, including pills, injections, and topical creams. Metronidazole is not FDA approved in dogs and its use in veterinary medicine is off label, which means vets may prescribe it even though it is not FDA approved. 

There are many generic forms of metronidazole available, which makes this medication relatively inexpensive. A prescription is required to obtain metronidazole. Pet owners can get this drug through their veterinary clinic or from a human pharmacy with a prescription from their veterinarian. Because metronidazole is widely used in human medicine, it is readily available, and pet owners can easily fill their dog’s metronidazole prescription at any human pharmacy.

What Does Metronidazole Look Like?

Owner holding pil for dog which is a dose of Metronidazole for Dogs

Because there are so many generic forms of Metronidazole available, the exact appearance of the pill will vary depending on the manufacturer. However, Metronidazole is typically a white round or oval-shaped tablet. Metronidazole also comes in both an oral liquid and in an injectable form, which is sometimes used for hospitalized patients. 

For humans, metronidazole comes in topical creams, gels, and lotions, as well. Though these formulations are generally not used in veterinary medicine.

How Does Metronidazole Work?

Dog holding paws on edge of railing smiling and feeling healthy

Metronidazole works by penetrating anaerobic bacteria cells and forming free radicals that inhibit DNA synthesis, causing the degradation of DNA and death of the bacteria. It is also effective against protozoal organisms. When given orally, metronidazole is absorbed from the GI tract and metabolized by the liver. 

Most dogs tolerate metronidazole well and experience little to no side effects. Your dog will generally begin to feel better within a few days of starting metronidazole. 

Remember that it is very important to give the full course of medication as prescribed by your veterinarian, even if your dog is feeling better, to ensure that your dog’s infection has completely resolved.

What is Metronidazole Used for in Dogs?

Dog looking sick while owner holds them waiting for a dose of Metronidazole for Dogs

Metronidazole is used to treat a variety of conditions in dogs including: 

  • Diarrhea
  • Giardia
  • Trichomonas
  • Inflammatory bowel disease
  • Enteropathy
  • Hepatic encephalopathy
  • Vaginitis

This medication is also sometimes used in combination with other antibiotics to help provide a more broad-spectrum antibiotic coverage. 

Metronidazole Side Effects in Dogs

Dog feeling sick between two people on the couch

Most dogs respond well to metronidazole with little to no side effects. Side effects that do occur tend to be mild and resolve soon after discontinuing the drug. If your dog experiences side effects after taking metronidazole, stop giving the medication and contact your veterinarian for further advice. 

Side effects of metronidazole in dogs include:

  • Loss of appetite
  • Vomiting
  • Excessive salivation
  • Stomatitis (inflammation of the mouth)
  • Loss of sense of smell
  • Hepatotoxicity (liver disease)
  • Candida overgrowth

Reactions With Other Drugs and Medications

Owner holding out medications to dog

Metronidazole should be used with caution in dogs taking certain medications due to the risk of adverse reactions. Metronidazole may cause interactions with medications such as:

  • Barbiturates
  • Phenytoin
  • Warfarin
  • Cimetidine
  • Lithium
  • Terfenadine
  • Astemizole
  • Vitamin K antagonists

If your dog is on any of the above medications, talk to your veterinarian before starting metronidazole. Your veterinarian may recommend starting on a lower dose of metronidazole or using a different medication to reduce the risk of a reaction.

Metronidazole Dosage for Dogs

Owner giving dog liquid medication from a dropper

The dose of metronidazole varies depending on the condition being treated and your dog’s weight. Follow your veterinarian’s dosing instructions closely to ensure your dog receives the correct dose of medication. Always complete the full course of antibiotics, even if your dog begins to feel better. 

Never give your dog metronidazole — or any other prescription medication — unless it has been prescribed by your veterinarian. Doing so may be harmful to your dog and may increase the risk of side effects.

What if My Dog Misses a Dose of Metronidazole?

Dog head tilted to camera outdoors

If your dog misses a metronidazole dose, continue on with the dosing schedule as prescribed. Do not double up doses or give your dog extra medication to account for the missed dose. 

If your dog misses more than one dose of medication, consult your veterinarian for advice on how to proceed. Your veterinarian may recommend restarting the course of antibiotics or adjusting the treatment plan to ensure your dog’s infection is addressed adequately.

Cost of Metronidazole for Dogs

Dog laying on bed looking out to the world

Metronidazole is available as a generic medication, so it is generally inexpensive. Pet owners should expect to pay about $20-$50 for a metronidazole prescription, depending on the tablet strength prescribed and the duration of the treatment prescribed. 

Metronidazole Storage Instructions

Metronidazole should be stored in a tightly sealed, light-resistant container at room temperature, away from moisture. Liquid formulations of metronidazole may need to be kept refrigerated. Be sure to read the packaging and follow the manufacturer’s directions for proper storage.