Metronidazole Side Effects in Dogs

Dogs suffering from symptoms such as diarrhea and vomiting might be prescribed metronidazole, a popular antibiotic and antiprotozoal 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.

Sad look of the old dog
Metronidazole Side Effects in Dogs
credit: Chalabala/iStock/GettyImages

While it's not approved by the Food and Drug Administration for use in pet medication, metronidazole is frequently recommended by veterinarians to treat a dog's inflammatory bowel disease, certain diarrheal disorders, periodontal disease, and infections caused by giardia, a single-cell parasite that could have been ingested by your dog through water or feces-soiled substances. Because the medication is not originally intended for dogs, you should be vigilant in observing any side effects that your pup might experience.

How does metronidazole work?

Flagyl comes in a HP 65 pill form (a white capsule filled with 250 mg or 500 mg of metronidazole), an oral solution, and an intravenous liquid. Once administered, metronidazole is activated after it's been diffused into bacterial cells and targets intestinal parasites and anaerobic bacteria, which are commonly found in the gastrointestinal track and 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.

How many days should I give my dog metronidazole?

The dosage and frequency of metronidazole will vary depending on your dog's unique medical needs. It's important to follow your vet's directions carefully. Do not deviate from the recommended dosage or imposed frequency. If you miss a dose, give your dog his 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.

Most dogs will not like the metronidazole pills' unpleasant, metallic taste, but avoid crushing the medication because it could cause excessive drool. Giving the medicine with food could help with absorption and could minimize gastrointestinal side effects. Metronidazole is not suitable for pregnant or lactating dogs as well as pups with anemia, epilepsy, nerve disorders, or liver, kidney, or Lyme disease. Store capsule medication at room temperature away from moisture and heat.

What are the Flagyl side effects?

While metronidazole is meant to remedy a dog's gastrointestinal system, it can also cause adverse side effects, including vomiting, nausea, and loss of appetite. Your dog might also drool excessively, sneeze, become lethargic, lose balance, expel darker than usual urine, or experience dizziness, runny nose, or dry mouth. Call your vet immediately if your dog suddenly has difficulty breathing, develops hives, or if her 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, and watery or bloody diarrhea. In most cases, overdosage is the cause of the serious side effects.

What is metronidazole neurotoxicity?

Dogs that have received high or prolonged doses of metronidazole or pups with liver disease might develop metronidazole neurotoxicity, which is considered fairly common with this drug. Call your vet immediately if your dog is staggering, experiences paralysis, has seizures, or if his eye moves rapidly back and forth. In "Small Animal Toxicology," published in 2013, veterinarian Kevin T. Fitzgerald wrote that "metronidazole toxicity is closely dose related, following inappropriately high doses, inappropriate long-term administration, or both." He also stated that animals have shown completed recovery in 14 days after the drug treatment was stopped. In a small 2003 study conducted by the Veterinary Neurological Center, researchers found that dogs prescribed diazepam, the generic name for Valium, recover quicker than dogs that simply stopped taking metronidazole. In rare cases, a dog might need to be hospitalized.