How many days should I give my dog metronidazole?

Whether it’s from an infection or finding something rotten in the backyard, dogs are no strangers to stomach issues. When they show signs of intestinal distress, sometimes the best answer is metronidazole (brand name: Flagyl), a type of nitroimidazole antibiotic.

Technically, treating animals is an off-label use for this antibacterial and antimicrobial drug, but metronidazole works for anaerobic bacteria infections, inflammatory bowel disease, giardia, acute diarrhea, and dental infections. The dosage is often 5–10 mg for every pound of body weight, although it can vary depending on the condition. Here’s everything you need to know about metronidazole dosage for your furry companion.

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Metronidazole dosage for dogs

Like many medical treatments, there’s no one-size-fits-all approach to metronidazole treatment. Dr. Emily Seidel, DVM, DACVIM, a Colorado Animal Specialty & Emergency veterinarian, says it’s typically dosed based on a pet’s body weight. “Dosing based on a pet’s size is extremely important since we treat anything from kittens to Great Danes,” she says. “We have certain thresholds at which we see toxicity, and we use doses lower than this to mitigate these adverse effects.” 

For other conditions, the Merck Veterinary Manual says the safest and most effective doses are as follows:

• Giardiasis: 25 mg/kg every 12 hours
• Inflammatory bowel disease (IBD): 10–15 mg/kg every 12 hours
• Hepatic encephalopathy: 7.5 mg/kg, every 8–12 hours

Because metronidazole may affect the liver and kidneys, vets usually give it in lower doses or avoid it entirely for dogs with pre-existing kidney and liver disease. It’s also unsafe for pregnant or nursing dogs and young puppies, per the American Kennel Club.

Metronidazole also has drug interactions with several other medications, including cyclosporine, phenobarbital, and phenytoin. Certain supplements, flea medications, and chemotherapy drugs may also cause adverse reactions.

How much metronidazole can I give my dog?

According to the American College of Veterinary Pharmacists, much of the literature on metronidazole toxicity says it can occur at around 60 mg/kg/day. However, they also say some research has shown toxicity at lower doses, such as this 2018 study, which recommended caution with doses greater than 40 mg/kg/day. Only give a dog more than that if the veterinarian specifically prescribes it.

While the dosage depends on the condition it’s treating, here’s what the American College of Veterinary Pharmacists recommends for safe metronidazole administration based on your dog’s weight.

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How long should I give metronidazole to my dog?

After you’ve answered, “How much?” The next important question is, “How long?” Most often, the use of metronidazole is short-term—typically around 5–10 days. 

“Metronidazole is a very effective medication; however, overuse can be dangerous,” says Dr. Amy Attas, veterinarian and author of Pets and the City: True Tales of a Manhattan House Call Veterinarian. “Prolonged use may disrupt the gut microbiota, which can negatively affect a dog’s digestive health.” Studies have demonstrated those digestive tract changes and suggest a cautious approach when prescribing the drug. 

Aside from dysregulation of the bacteria found in the GI tract, Dr. Seidel says long-term use “can also contribute to antibiotic resistance, which is an important topic in an increasingly antibiotic-resistant world.”

But there are less common risks, too. Per Dr. Attas, “In rare instances, high doses or prolonged use can lead to liver toxicity, even if initial doses are well-tolerated,” and metronidazole can cause neurologic side effects as well, such as disorientation, inability to walk, and seizures. 

The exact duration depends on the condition being treated. However, dogs should only take the medication for longer than a week if the vet specifically directs it.

Overdose of metronidazole in dogs

Dogs may experience common side effects of metronidazole, including vomiting, diarrhea, drooling, gagging, fatigue, loss of appetite, and urine discoloration. Usually, these adverse effects are relatively harmless. Yet it’s also possible for a dog to overdose on metronidazole, no matter their size and condition, so owners have to be careful not to give them too much.

Metronidazole can pass through the blood-brain barrier, which means toxicity might manifest in terms of central nervous system symptoms. The signs of metronidazole toxicity include:

• Disorientation
• Ataxia (difficulty balancing)
• Head tilt
• Rigidity and stiffness
• Rapid eye movements
• Vomiting
• Extreme fatigue
• Seizures

If you notice any of these serious side effects, it’s important to contact the vet immediately. Dogs can fully recover from metronidazole overdose, but only if they receive the proper medical attention and treatments.

Guidelines for administering metronidazole in dogs

The best way to administer metronidazole is by mouth or with food. Technically, dogs can take it without food, but a full belly can reduce the chances of gastrointestinal side effects. Of course, that’s easier said than done since dogs don’t always like taking medications. Plus, metronidazole is bitter, says Dr. Attas, so dogs might not want to take it. 

“Find a food that is irresistible to the dog and try molding it around the pill,” she suggests. “Give the dog a few small treats of this food without pills inside, so they are excited for the next treat. After eating the treat-wrapped pill, follow up with a few empty treats so they are not suspicious for the next treatment.”

If that doesn’t work, she says you can approach the dog from behind, lift the head, open the dog’s mouth, and put the pill as far back as possible, then quickly remove your hand since even friendly dogs may mistakenly bite in an attempt to get a hand out of their mouth. 

If you miss a dose of metronidazole, give it as soon as possible. However, if the dog’s next dose is only a few hours away, just wait. Never give a dog a double dose to make up for a missed one because it could cause an accidental overdose.

Metronidazole’s half-life in dogs can be anywhere between three and 13 hours, so it can stay in their system for up to 26 hours after treatment. Any side effects should subside within around a day after stopping treatment.