How many days should I give my dog metronidazole?

In this article:

• Dosage for dogs
• How much metronidazole can I give my dog?
• Treatment duration
• Overdose
• Administration guidelines

In this article

• Dosage for dogs
• How much metronidazole can I give my dog?
• Treatment duration
• Overdose
• Administration guidelines

Whether it’s from an infection or finding something rotten in the backyard, dogs are no strangers to stomach or bowel issues. When they show signs of intestinal distress, the solution may be to give the dog metronidazole for 5 to 10 days. Metronidazole is a nitroimidazole antibiotic that not only kills bacteria but also kills some protozoans and reduces inflammation. Veterinarians commonly use it to treat Giardia intestinal infections, anaerobic bacterial infections, non-specific intestinal and stomach inflammatory conditions, and diarrhea. Here’s everything you need to know about how you should give metronidazole to your furry companion.

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Metronidazole dosage for dogs

Metronidazole dosages vary by condition, but usually range between 5–10 mg for every pound of body weight (10-25 mg/kg) given two and sometimes three times a day, depending on the condition. “Dosing based on a pet’s size is extremely important since we treat anything from kittens to Great Danes,” says Dr. Emily Seidel, DVM, DACVIM, a Colorado Animal Specialty & Emergency veterinarian. “We have certain thresholds at which we see toxicity, and we use doses lower than this to mitigate these adverse effects.” 

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

• Giardiasis: 25 mg/kg every 12 hours for five days
• Inflammatory bowel disease (IBD): 10–15 mg/kg every 12 hours
• Complications of severe liver disease (hepatic encephalopathy): 7.5 mg/kg, every eight to 12 hours

Plumb’s Veterinary Drug Handbook gives the following common dosages:

• Amoeba intestinal infections: 25 mg/kg every 12 hours for eight days
• Large bowel diarrhea: 20–25 mg/kg every 12 hours for five to 10 days

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. Plumb’s Veterinary Drug Handbook also cautions that prolonged use of metronidazole can lead to toxicity in dogs even at clinically-recommended moderate to high dosages. In conclusion, metronidazole has a low threshold for side effects, and dosage is calculated on a case-by-case basis. Doses usually start around 10-15mg/kg of body weight twice daily and do not typically exceed 25mg/kg of body weight twice daily. Your veterinarian will factor in the condition being treated, length of treatment, additional medications your pet is taking, and your pet’s coexisting medical conditions when prescribing a metronidazole dose. 

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How long should I give my dog metronidazole?

After you’ve answered, “How much?” The next important question is, “How long?” Most often, metronidazole is used for a short time, typically 5 to 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.” One study has demonstrated significant changes to a dog’s gut biome and suggests 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. A veterinarian may ask the pet’s parent to watch for neurological effects if metronidazole is used for too long.

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:

• Ataxia (difficulty balancing)
• Rapid eye movements (nystagmus)
• Problems with body position and movement (clumsiness, falls, bumping into things)
• Head tilt
• Dilated pupils
• Depression
• Lethargy
• Vomiting
• Joint knuckling (walking on the top of a paw)
• Rigidity and stiffness
• Tremors
• Seizures

If you notice any of these serious side effects, contact the vet immediately. Dogs can fully recover from a metronidazole overdose, but only if they receive the proper medical attention and treatment.

Guidelines for administering metronidazole in dogs

The best way to administer metronidazole is by mouth, with or without 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. 

Alternatively, you can give the dog a liquid version of metronidazole called Ayradia. FDA-approved to treat giardiasis in dogs, Ayradia is more expensive than generic metronidazole tablets or capsules. The expense may be worth it, because it’s easier to administer. It’s also harder for a dog to spit out a liquid medicine than a pill.

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 is 3-13 hours, so it can remain in their system for up to 26 hours after treatment. Any side effects should subside within around a day after stopping treatment.

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