Metronidazole For Dogs: Side Effects, Uses & Dosage

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Dogs suffering from symptoms such as diarrhea and vomiting might be prescribed metronidazole, a popular antibiotic and anti-protozoal medication. Often sold under the brand name Flagyl, metronidazole was initially developed for humans to treat bacterial infections of the joints, skin, vagina, stomach, and respiratory tract.

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While it's not approved by the U.S. Food and Drug Administration for use as a pet medication, the FDA allows metronidazole to be used off label for veterinary medicine. Your DVM may prescribe metronidazole to treat several common conditions such as:

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  • a dog's inflammatory bowel disease
  • certain diarrheal disorders
  • periodontal disease
  • giardia infection, a single-cell protozoan parasite that could have been ingested by your dog through water or feces-soiled substances.

Because the original uses of metronidazole were not intended for dogs, pet parents should be vigilant in observing any side effects that your pup might experience.

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How does metronidazole for dogs work?

Metronidazole comes in pill form, an oral solution, and an intravenous liquid. There are different uses for metronidazole, but it's typically prescribed to treat gastrointestinal tract issues in dogs. If your dog is taking the pill form, store it at room temperature. The compounded liquid needs to be refrigerated.

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Once administered, metronidazole is activated after it has been diffused into bacterial cells and targets intestinal parasites and certain anaerobic bacteria, which are microorganisms commonly found in the gastrointestinal tract that do not require oxygen to live. The medication also has the ability to cross the blood-brain barrier to treat central nervous system infections and to penetrate bone, which is useful when dealing with dental infections.

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How many days should you give a dog metronidazole?

The dosage and frequency of metronidazole will vary depending on your dog's unique medical needs. It's important to follow your veterinarian's directions carefully. Do not deviate from the recommended dosage or imposed frequency. If you miss a dose, give your dog their medication as soon as you remember unless it's close to the time of the next dose. You want to avoid giving your dog twice the dosage at one time. Overdosing can cause nausea, vomiting, dizziness, seizures, or loss of balance or coordination.

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Most dogs will not like the metronidazole pills' unpleasant, metallic taste so avoid crushing the medication because it could cause excessive drooling. Giving the medicine with food could help with absorption and could minimize possible side effects. Metronidazole is not suitable for pregnant or lactating dogs, puppies, and dogs with epilepsy or certain liver disorders. Because of drug interactions, it should not be given to dogs on blood thinners. Store capsule medication at room temperature away from moisture and heat.

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What are the common side effects of metronidazole for dogs?

While metronidazole is meant to remedy a dog's gastrointestinal tract, it can also cause adverse side effects. The side effects of metronidazole include:

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  • vomiting
  • nausea
  • diarrhea
  • loss of appetite
  • drooling excessively or gagging due to the bitter taste
  • becoming lethargic
  • experiencing balance issues
  • expelling darker than usual urine
  • dizziness
  • dry mouth

Other potential side effects can be serious. Call your veterinarian immediately if your dog suddenly has difficulty breathing or develops hives or if their face, lips, tongue, or throat swell up. This could indicate an allergic reaction to the medication. More severe side effects include seizures, fever, chills, mouth or lip sores, tremors, rapid eye movements, and watery or bloody diarrhea. In most cases, overdosage, which can be life-threatening, is the cause of the serious side effects.

What dog parents should know about metronidazole neurotoxicity

Dogs who have received prolonged or high doses of metronidazole or pups with liver disease might develop metronidazole neurotoxicity, which may lead to adverse effects. Call your veterinarian immediately if your dog is staggering; experiences paralysis; has seizures, tremors, or muscle spasms; or if their eyes move rapidly back and forth.

Metronidazole toxicity is most frequently caused when dogs receive higher doses of the drug. Signs of toxicity in dogs are spotted most often when they receive doses over 60 milligrams/kilogram per day, though toxicity has also been reported in dogs receiving as little as 26 milligrams/kilogram per day.

The bottom line

While metronidazole is not approved by the FDA for animal use, it's commonly used in dogs with giardia and gastrointestinal issues. It can eliminate certain protozoan parasites and harmful bacteria and can also be used to treat dental infections. Your veterinarian should be consulted if your dog experiences unusual or severe side effects, such as difficulty breathing; hives; swelling of the face, lips, tongue, or throat; seizures; fever; chills; mouth or lip sores; tremors; rapid eye movements; or watery or bloody diarrhea.

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