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    PeterDobias.com / Blog / health knowledge

    The most common diarrhea drug is harmful to your dog's gut

    By Dr. Peter Dobias, DVM

    Dr. Peter Dobias, DVM has 30 years of experience as a veterinarian. His love of dogs and passion for natural healing and nutrition led him to writing, teaching and helping people create health naturally, without drugs, chemicals and processed food.

  • 1. A - The Study Summary
  • 2. B - What to do when your vet suggests metronidazole?
    • 3. C - An alternative treatment plan for acute or chronic diarrhea, diet allergies or leaky gut
      • What to do when your vet wants to prescribe metronidazole?

        One of the biggest challenges to the progression of veterinary medicine is a lack of scientific evidence that drug-based medicine and processed food are harmful to the health of your dogs. The main reason is that the drug manufacturers are unlikely to put any money into research that would threaten the viability of drugs they make and their bottom line.

        I am also convinced that even so-called conventional veterinarians would be interested in alternative treatment methods if supporting research was more available. However, there are not many entities willing to fund such research. This strange paradox has led to a drug-based, lopsided evolution of medicine where disease is an asset and health is an obstacle to the big pharma.

        The only entities that can move medicine towards a more natural, common sense, and chemical-free direction are researchers at universities, however, they too have been strangled by the tentacles of the almighty big pharma industry that refuses to let go.

        However, there are some exceptions and that is why I am grateful to the brave and daring research team that recently published a study that shows that the antibiotic drug, metronidazole, one of the most commonly used drugs to treat Giardia, Clostridia, and diarrhea in general, causes serious long-term disturbances of the intestinal metabolism and microbiome. Unfortunately, this drug is often given without any concrete evidence that a specific pathogen sensitive to this antibiotic is present.

        The study is called the “Effects of metronidazole on the fecal microbiome and metabolome in healthy dogs” and it was published on August 28, 2020. Paradoxically, the study showed that the drug itself often causes diarrhea and digestive disturbances if administered to healthy, asymptomatic dogs.

        The purpose of this article is to:

        A. Highlight some of the most important findings in the study.
        B. Give you a plan of action and what to do when your vet proposes metronidazole for your dog.
        C. Provide you with A Complete Guide to Treating Chronic and Acute Diarrhea in Dogs that is proven by more than 23 years of clinical practice.

        A - The Study Summary

        The effects of metronidazole on intestinal microflora and intestinal health in dogs

        The dogs in the study have been divided into 3 groups
        • G1 – Dogs where no treatment was given or diet changes were made
        • G2 – Hydrolyzed protein diet and metronidazole were administered
        • G3 – Metronidazole was given to this group.
        The research team based their study upon the fact that healthy digestion and immune function greatly depends on intestinal microflora. These beneficial bacteria produce Short Chain Fatty Acids (SCFA) that are an essential energy source for proper intestinal function and helps reduce inflammation.

        The study involved 24 dogs aged 1 – 10 years who had NO symptoms of diarrhea or digestive problems at the start of the study.

        The study methods

        Fecal and blood samples were collected throughout the six-week course of metronidazole and for 4 weeks after the administration ended.

        Evaluation parameters

        The following parameters were evaluated:


        1. Clinical findings and the presence of diarrhea
        2. The quantity and diversity of beneficial intestinal bacteria
        3. Short Chain Fatty Acids (SCFA)
        4. The population of Clostridium Perfringens – a pathogenic bacteria
        5. The levels of cobalamin and folate – vitamins that correlate with the degree of intestinal health
        6. The levels of bile acids that play a key role in fat digestion and absorption of fat-soluble vitamins
        7. Lactate as a measure of oxidative stress and antioxidant levels

        1. Clinical Findings

        More than half of the dogs on metronidazole developed diarrhea two to three days after the start of the experiment. (This is rather surprising considering the medication is used for treating diarrhea in dogs.)

        2. The quantity and diversity of beneficial intestinal bacteria
        There was a significant decrease in the beneficial intestinal flora count and diversity that persisted for weeks after the metronidazole was stopped. Some of the bacterial species have not fully recovered even later than four weeks after discontinuing metronidazole.

        3. Short Chain Fatty Acids (SCFA)

        SCFA are produced by beneficial bacteria from dietary fibre and are the key to healthy digestion, they decreased during the course of metronidazole. SCFA are an important source of energy for the intestinal lining and leaky gut prevention.

        4. Bacterial effect on Clostridium Perfringens

        The bacteria that metronidazole is often used against didn’t seem to decrease in numbers during the experiment. Ironically, the number of Clostridium Hiranonis, a bacteria that has a positive effect on digestion and takes part in bile acid production, decreased during the experiment and did not fully recover within four weeks following the study.

        5. Fecal metabolites (biochemical components)

        65 metabolites were significantly impacted by metronidazole administration including bile acids, vitamins, nucleobases (vital components of DNA and RNA), and antioxidants. The levels were significantly lower even 4 weeks post metronidazole, which suggests long-term side-effects of metronidazole.

        6. Bile Acids Levels

        Bile acid levels decreased in the group on metronidazole, and these levels have not returned to normal by the end of the experiment in 4% of dogs. Bile acids are an important component of intestinal health, namely fat digestion and fat-soluble vitamin absorption. Lower levels of bile acids also increase the chances of pathogenic Clostridium infections.

        7. Lactate and antioxidant levels

        The decrease of beneficial bacteria directly correlated with the increase of lactate. This may be due to increased acidity caused by lactate. Laboratory results also showed a decrease in antioxidant levels, which is a sign of increased oxidative stress.

        Summary of findings

        Based on the above findings, it is very clear that metronidazole is not a good choice for dogs with diarrhea. It had a negative effect on the intestinal microbiome, intestinal motility, and immune function, in Groups 2 and 3 when compared with the control Group 1. This study also confirmed that a hydrolyzed prescription diet had neither a positive nor negative effect on the outcome of the study.

        The results of the study support my decision many years back to not recommend or use metronidazole in the treatment of acute and chronic diarrhea, inflammatory bowel disease, and leaky gut in dogs.

        B - What to do when your vet suggests metronidazole?

        First, remember that most veterinarians are reasonable and consider you and your dog’s health to be the main focus. If your veterinarian suggests a metronidazole prescription, ask if they have come across this metronidazole study, and share the original link here (https://onlinelibrary.wiley.com/doi/10.1111/jvim.15871).

        If your vet insists on the metronidazole prescription, politely decline if you feel that is the best choice for your dog and ask if you could manage your dog’s diarrhea with hydration, fasting and a “pumpkin and broth diet” until blood work and fecal tests are available to make a more targeted decision and consider other treatments.

        In the event that your dog already received metronidazole, administer a double dose of GutSense®, canine-specific pre and probiotics to restore your dog’s microbiome and also maintain it with regular dosing after 1 month. I have formulated this probiotic with the specific nature of the canine digestive tract in mind and give it to my dog Pax daily to maintain his digestive and immune system health.

        C - An alternative treatment plan for acute or chronic diarrhea, diet allergies or leaky gut

        Imbalances of gastrointestinal flora (dysbiosis), diet allergies, inflammatory bowel disease, and leaky gut, are a result of multiple factors including inappropriate diet, use of medication, stress, and nutritional deficiencies.  

        The good news is that most dogs can be effectively treated without antibiotics and fully recover.

        Here is your free, complete guide to treat diarrhea, inflammatory bowel disease, and leaky gut

        Featured products related to this article

        Dr. Peter Dobias, DVM has 30 years of experience as a veterinarian. He graduated as a Doctor of Veterinary Medicine in 1988 in the Czech Republic and obtained the Canadian Certificate of Qualification in 1995. He is currently licensed in the European Union, and his unique approach to healing and nutrition helps holistically minded dog lovers worldwide.

        Dr. Dobias strongly believes that disease prevention, natural nutrition and supplements, the right exercise and a drug free approach to medicine can add years to your dog's life.

        As a formulator of his all-natural vitamin and supplement line and co-inventor of natural, chemical free flea and tick control, FleaHex® and TickHex®, his unique healing system and products currently hold the highest independent five star customer rating. For more information click here.

        Any general recommendations that Dr. Dobias makes are not a substitute for the appropriate veterinary care and are for informational and educational purposes only.

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