Pet with diarrhea? Maybe hold off on the antibiotics

Updated October 17, 2022

New insights into the trillions of microbes comprising the intestinal microbiome are, among other things, calling into question the use of antibiotics to treat diarrhea in canine and feline patients.

Dr. Jennifer Granick, an associate professor of small animal internal medicine at the University of Minnesota College of Veterinary Medicine, suggested that treatment should focus instead on restoring the health of the complex system of bacteria and other microbes within the gastrointestinal tract.

“When I went to veterinary school, we were taught to use metronidazole for diarrhea, and what I hope to convince you of is that, maybe, we should be think rethinking our approach,” Dr. Granick said during her presentation, “First Do No Harm: A New Approach to Diarrhea in the Dog and Cat,” July 30 at AVMA Convention 2022 in Philadelphia.

Veterinarian examining a Dachshund

The gut microbiome has been shown to be an essential part of host health. As Dr. Granick explained, these microbes create defensive barriers against potential pathogenic organisms, aid in nutrient breakdown and energy release from ingested foods, provide nutritional metabolites for enterocytes, help regulate immunity, and metabolize substances the host can’t, such as drugs.

Gut microbiota in dogs and cats consist primarily of the genus Firmacutes, Bacteroides species, and fusobacteria, Dr. Granick said. The canine GI tract contains large amounts of Enterococcus and lactic acid–producing species, whereas Lactobacillus, Enterococcus, and Bifidobacterium species are found within the feline GI tract.

Gut heath is not a novel idea in veterinary medicine, Dr. Granick said, noting how withholding food was thought beneficial in cases of parvovirus infection and pancreatitis.

“We don’t do that anymore because there are plenty of studies that say early enteral feeding is more helpful for getting these animals well sooner,” she said. “The key to that is feeding the gut because the gut needs the bacteria to eat in order to stay healthy.”

A growing body of research shows antibiotics have little or no impact in cases of acute diarrhea and hemorrhagic diarrhea syndrome. In fact, evidence suggests infection-fighting medications can aggravate the microbiome, similar to infection, inflammatory disease, and poor diet.

What are the alternatives to antibiotics? Prebiotics—that is, substances fed to the microbiome to get it back on track. High-fiber pet diets and psyllium additives fall in this category. There are also probiotics, or “good bacteria,” Dr. Granick explained. The result of these two is post-biotics, which include metabolites, short-chain fatty acids, and functional proteins.

Fecal microbiome transplantation is another potential option, but it’s a relatively new procedure with much to be learned, according to Dr. Granick. “Screening your donors is so important,” she cautioned, “not only for fecal pathogens but also making sure they don’t have a long history of antimicrobial use.”

What does Dr. Granick do when presented with a case of acute diarrhea? She prescribes a highly digestible diet, probiotics, plus or minus prebiotics, and deworming, depending on the patient’s history.

In chronic cases, her initial approach is to go with either a highly digestible diet or a high-fiber diet. “My decision making really depends on what has already been tried,” Dr. Granick said “Oftentimes, when I’m seeing patients with chronic diarrhea, they’ve gone through a few different treatment trials first. And I’ll make my decision about diet depending on what’s already happened.”

Additionally, Dr. Granick prescribes both prebiotics and probiotics, runs a blood test to determine whether a B12 supplement is needed, and deworms the patient. If the patient is hypoalbuminemic, and Dr. Granick thinks the animal has protein-losing enteropathy, she begins immunosuppressive treatment. If the patient isn’t responding to the treatment, then Dr. Granick does additional diagnostic testing.

The last thing Dr. Granick tries is antibiotics. “That’s not to say there aren’t antibiotic-responsive diarrheas out there. There absolutely are,” she said. “But antibiotics are the last thing I do, which is really different than when I first started practicing because it was the first thing I did.”

Correction: A previous version of this story misspelled the word psyllium.

A version of this article appears in the October 2022 print issue of JAVMA.