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What is Metronidazole and When Should I Use it on My Dog?

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Doctor DebVerified

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Veterinary Medicine

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Metronidazole Uses

Metronidazole is mostly for dogs suffering from inflammatory bowel disease. It is also used to treat diarrheal disorders, infections caused by Giardia, and even gum disease.

Metronidazole is a prescription only medication classified as an antiprotozoal and antibiotic. This means that the medicine fights both protozoa (simple organisms) and anaerobes (organisms that don’t need air). Metronidazole, the generic name of the drug, has multiple prescription names: Metizol, Flagyl, Protostat, and Metrogel.

A worried dog hides under a blanket

Metronidazole is often prescribed for dogs and cats. Vets use this medicine when pets present with issues affecting the intestine like inflammatory bowel disease (IBD), diarrhea, and giardia, as well as run of the mill infections like periodontal disease (gum disease). Veterinarians may also use it for pets who display signs of bacterial infection or liver issues, as well as for those with internal parasites.

How metronidazole works

As an antibiotic, metronidazole works by destroying infectious organisms that can attack a pet's intestinal tract or central nervous system. Although scientists don’t understand the exact mechanism of action in the drug, it has enjoyed widespread use by veterinarians and is a trusted treatment option. Metronidazole is taken up by anaerobic organisms when it’s introduced into the dog. Inside the organisms, it is reduced to a compound. Doctors believe that this compound is responsible for the drug’s antimicrobial activity by disrupting DNA and nucleic acid synthesis in the bacteria.

Metronidazole usage and dosing information

The proper dosage depends on several aspects: the dog’s age, weight, and size, and the condition for which the dog is being treated. Your veterinarian can provide the proper dosage information for your dog, as seizures and neurological problems can occur if the dose is too high or if the drug is given long term. If your dog is showing signs of neurological malfunction, call your veterinarian.

Generally, however, doctors recommend giving dosages of 5-15 mg per pound of dog, depending on the illness. This would mean that a 25lb dog may take a 250 mg pill per dose. Metronidazole usually comes in either 250 mg tablets or 500 mg tablets.

The tablet form tends to be bitter, so prepare yourself for the unpleasant experience of trying to coax your dog to take it. Some sources advocate crushing up the tablets and mixing with food; try this at your own peril, however, as some dogs will refuse to take any food that tastes bitter. You may have more luck stuffing the pill inside a treat, like a piece of cheese, a hotdog, or a meatball. Metronidazole is also available in a compounded flavored pill which many vets carry.

A dog awaits his food being filled

Always administer metronidazole at the same time every day to avoid a missed dosage.

Metronidazole side effects

Most of the potential side effects associated with metronidazole – drooling, gagging and pawing at the mouth – happen because the dog does not like the taste of a crushed pill. If you succeed in hiding a whole pill inside food for your dog, she should not experience any of this discomfort. As it stands, discomfort with the taste of the drug generally lasts for a short time. Contact a veterinary Expert if you see possible side effects like these:

Common side effects:

  • Vomiting
  • Lack of – or decrease in – appetite
  • Diarrhea
  • Energy loss

Rare but serious side effects:

  • Balance issues
  • Head tilt
  • Slow irregular heartbeat
  • Dilated pupils
  • Muscle stiffness
  • Seizures
  • Bloody urine

Although extremely rare, it is possible for dogs to have allergic reactions to this drug. Allergies may indicate as rashes, hives, difficulty breathing, or swelling. If you suspect your pet is having an allergic reaction, see your vet as soon as possible. Never wait a few days for the reaction to pass.

Additionally, talk to your veterinarian before administering the drug if your pet has a history of liver disease or kidney disease. Liver damage as a result of metronidazole interaction is highly unlikely but possible. Otherwise healthy dogs should have no issues taking metronidazole for their medical condition.

Neurotoxicity caused by metronidazole

Dogs who take metronidazole for extended periods of time may experience signs of neuropathy, or nerve damage, in the ears and feet. A significant overdose can also cause neurological problems.

Signs of toxicity consist of appetite loss, vomiting, lack of balance, rapid eye movement, disorientation, muscle stiffness, and seizures. If your dog is has any of these symptoms, contact a veterinarian immediately.

Metronidazole food and drug interactions  

Veterinarians have used this medication extensively for a number of years to treat many types of canine illnesses. Still, metronidazole has not been approved by the Food and Drug Administration (FDA) for use in dogs.

A small cluster of white and yellow pills

Most vets do not recommend administering metronidazole to puppies, pregnant, or nursing dogs. This medicine may have adverse effects on unborn fetuses.

Harmful drug interactions with metronidazole include Tagamet (Cimetidine), Dilantin (Phenytoin), Warfarin (Coumadin), Phenobarbital (Pb), as well as other drugs. Advise your veterinarian of all other medications your dog is taking or may be allergic to.

Do not use metronidazole alongside other antibiotics.

Consult a veterinary Expert if you suspect your dog has overdosed of metronidazole. For emergencies call American Society for the Prevention of Cruelty to Animals (ASPCA) Poison control hotline (888-426-4435).

Forgetting a dose of metronidazole

If you notice you have accidentally missed a dose, contact an Expert to get instructions. Never give your dog a double dose of metronidazole. Double dosing may cause dogs to develop significant adverse reactions.

Metronidazole storage and disposal information                       

Metronidazole tablets, or extended-release capsules, must be kept at room temperature, in a tightly closed container. Keep liquid forms refrigerated. Keep out of the reach of children and pets. Your pharmacist or veterinarian can dispose of any medication that is outdated or no longer usable. Do not use outdated medications.

Metronidazole can treat many forms of infections in dogs and other animals. Its ability to penetrate the blood-brain barrier makes it especially effective in the fight against anaerobic bacteria. Still, watch for any changes in your dog while taking this medication. Always follow your veterinarian’s instructions and do not self-medicate your dog. For other medical questions about your dog, ask a veterinary Expert.

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