Dog gets diarrhea, then dog gets metronidazole (or another antimicrobial).

That’s a pretty rote approach to diarrhea in many areas, and one we’ve been battling for years, because there’s no evidence that antibiotics help dogs in these cases (and increasing evidence that they might even hurt).

Trying to get veterinarians NOT to prescribe antimicrobials in these cases leads to a lot of pushback, less because people are convinced in their minds that antimicrobials works – but it’s more because “it’s what we’ve always done” and because “owners will be upset if I don’t do something.”

We’re programmed to want to “do something,” even though doing nothing is often the best approach. Try thinking about it this way: when you or your child gets diarrhea, do you rush to the doctor? No. If you’re otherwise healthy, you wait it out and it almost always gets better on its own.

Why do we rush our dogs to the veterinarian quicker than we take our kids to the doctor? Because dogs don’t use the toilet. Owners see the diarrhea (and often need to clean it up) and it’s gross, so the feel they need to do something as soon as possible.

A recent paper (Pegram et al, PLOS One 2023) is an important addition to our knowledge about treating diarrhea in dogs, and is more support for the “do nothing” (in terms of prescribing antimicrobials) approach.

The study was a “target trial emulation” that used electronic medical record data from over 1800 veterinary clinics in the UK to evaluate the impact of antimicrobials and nutraceuticals on resolution of acute diarrhea in 894 dogs between 3 months and 10 years of age. The nutraceutical group included use of prebiotics, probiotics, synbiotics (i.e. combinations of prebiotics and probiotics), adsorbents and motility modifiers.

Neither antibiotics nor nutraceuticals had a significant impact on diarrhea.

The initial clinical response rate for dogs with antibiotics was 88.5% vs 87.4% for those that didn’t receive antibiotics. For nutraceuticals, the numbers were 88.3 vs 86.9%.

Even in their final statistical model, which controlled for a range of factors, there was still no impact of antimicrobials or nutraceuticals on resolution of diarrhea. The risk difference for clinical resolution in dogs that were treated with antibiotics versus those that were not treated was non-significant and clinically trivial (0.4%). The same was true for nutraceuticals.

Sometimes, as clinicians, we get bogged down worrying about the “what if?” component (i.e. “what if I don’t treat the dog and the diarrhea gets worse?“). So the researchers also computed the need for, and time to, escalation of treatment. There were no significant impact of antimicrobials on whether dogs needed their care escalated (e.g. their diarrhea or other clinical signs persisted or got worse) or how long it took for that to occur. The graph below shows the antibiotic (A=1) and non-antibiotic (A=0) groups marching along in parallel.

Interestingly, when they computed this for nutraceuticals, there was an increase in the risk of a need for treatment escalation in the nutraceutical group. The difference was minor and probably not really relevant clinically, but the difference was heading in the wrong direction.  

Overall, these findings are not too surprising, particularly the lack of benefit of antimicrobials, but this study is yet another reminder that we have little to no need to use antimicrobials in dogs with acute diarrhea.

The nutraceutical side of the equation needs further exploration. Evidence supporting the value of nutraceuticals (especially probiotics) in acute diarrhea in dogs has been weak to non-existent, and there is precedent from studies in other species that probiotics might delay recovery of the normal gut microbiota. This study combined a range of nutraceuticals, so we can’t say anything specific about probiotics or other products, but it highlights that these treatments need to be properly evaluated. “It can’t hurt” might not be true for probiotics in cases of acute diarrhea.

A good news part of this study was that only 40% of dogs with diarrhea received an antimicrobials. That’s lower than other studies, and suggests we’re making progress (albeit slowly). It also shows we still have a long way to go.

Will this study change anything? It’s hard to say. The issue is probably less a need for veterinarians to understand the science than reluctance to change. Sometimes with antimicrobial stewardship, the science is the easy part. Dealing with the human brain and human habits is the bigger challenge, and that’s a lot harder to address.