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Metronidazole for Dogs and Cats


Diarrhea is one of the most common clinical signs in dogs and cats, and it is one of the most common reasons why you might need to bring your pet to see his or her veterinarian.

In some cases, the diarrhea may be caused by something that they ate, and it can be self-limiting after a few days. This means that the diarrhea can improve without medical intervention. However, diarrhea can persist for longer periods of time, indicating that there may be another underlying cause. For diarrhea that persists your veterinarian may prescribe a bland diet, probiotics, and a medication called metronidazole. 

Diarrhea in pets

In this article we explore how the medication metronidazole works, any possible side effects to take into account, and the situations in which your veterinarian may prescribe metronidazole for your cat or dog. 

What is metronidazole?

Metronidazole is an antibiotic medication that is prescribed for certain types of infections. Infections of the gastrointestinal tract are most common, but there may be other situations where metronidazole is necessary. It is also an antiprotozoal medication, which means that it will help to treat an infection caused by a protozoan. Protozoa are single-celled organisms that can behave like parasites in dogs and cats. 

Metronidazole is effective against bacterial infections in the gastrointestinal tract because it works best against anaerobic bacteria. These are bacteria that function without the presence of oxygen in their environment. Some of the bacteria that can affect dogs and humans like Clostridium difficile can be treated with metronidazole. 

How and when is metronidazole prescribed?

Metronidazole is available in the form of an oral tablet or capsule, and it is also available in an injectable form that can be given intravenously to sick patients in a hospital setting. If an oral liquid medication is desired, the veterinarian can have a special formula created by a compounding pharmacy. 

Many veterinarians will prescribe metronidazole for pets with diarrhea. In most cases, pets develop diarrhea due to an infection or stress. There is a wide variety of bacteria present in the gastrointestinal tracts of dogs and cats. When inflammation is caused by stress, or if there is harmful bacteria present, some of the gut bacteria can leak toxins into the body, causing illness. If diarrhea persists for more than a day or two, a prescription for metronidazole may be necessary. 

Certain protozoan infections can also cause diarrhea, but metronidazole is primarily prescribed to dogs and cats when Giardia or Trichomonas infections are confirmed. Trichomonads will infest the intestinal tract or urogenital tract whereas Giardia mostly affects the intestinal tract. These parasitic protozoans can come from soil, water, and contaminated food. Metronidazole is able to kill both bacteria and these protozoans because they share the same fermentation enzyme that is targeted by metronidazole. 

Some studies suggest that metronidazole has some immune-modulating effects. This means that it plays a role in helping the immune system to function normally. Pets with inflammatory bowel disease develop diarrhea as a result of immune-modulated response against dietary proteins or intestinal bacteria. Metronidazole can be helpful in some of these situations. 

Precautions and possible side effects when using metronidazole

When the correct dose of metronidazole is prescribed, the risk of side effects is very low. Metronidazole is best given with food to avoid drooling, nausea, and vomiting. The tablet formulation can be very bitter-tasting when crushed up, so try to avoid crushing the tablet if possible. 

Overdoses of metronidazole may cause neurologic problems such as dizziness or stumbling when walking. In severe cases, it can cause eye twitching, tremors, and seizures. If you suspect that your dog or cat has been overdosed with metronidazole, it is important to contact your veterinarian right away.

In rare instances, metronidazole may cause a skin reaction that results in skin inflammation, bumps, and bruising in different areas. Metronidazole should not be given to pets who are nursing or to pets who have had an allergic reaction to it in the past. It can be used with caution in puppies and kittens, and it is okay to use in pets with liver disease or who are pregnant or on blood thinners as long as you have the approval of your veterinarian. If you yourself are pregnant, make sure to handle the medication with gloves on. 

Metronidazole is given every 12 to 24 hours, but its duration of effect may last slightly longer in pets with liver or kidney disease. It can affect the way that other medications are metabolized, so be sure to tell your vet if your dog is taking any immunosuppressives like cyclosporine, anti-seizure medications like phenobarbital, or chemotherapeutic agents for the treatment of certain cancers.  

Can I purchase metronidazole over-the-counter? 

Metronidazole is a prescription medication, which means that it is not available for purchasing over the counter. Over the counter medications can be purchased by the general public from any store or pharmacy, but prescription medications need to be specially purchased through a pharmacy that follows the directions regarding dosing and quantity from your veterinarian. 

dog medication

If metronidazole were available over the counter, it would increase the risk of antibiotic resistance due to overuse. Doctors are working to prevent antibiotic resistance and superbugs from developing by focusing on antibiotic stewardship. This is an effort to avoid the over-prescribing of antibiotic medications. Your veterinarian will need to carefully determine when and when not to prescribe antibiotics like metronidazole. Not every pet with diarrhea will need metronidazole. Many will improve on their own while others may get better with a bland diet, probiotics, and time.

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