Acute diarrhea is pretty common in dogs. It’s pretty common in people too, but our approach in dogs versus people is VERY different:

  • Diarrheic dogs often get taken to a veterinarian ASAP.
  • People with acute diarrhea rarely go to a physician.

Why is the approach so different?


It has nothing to do with severity of disease or need for healthcare. It (mostly) comes down to a simple fact: People use toilets and dogs don’t.

Diarrhea is gross, so dogs with diarrhea evoke a visceral response, i.e. “Ugh… I want this fixed now!” That’s particularly true when dogs have accidents in the house. Frequency of diarrhea is another issue: If you have to run to the bathroom every hour or two, it’s annoying but not horrible. If your dog needs to be let out every hour or it poops in the floor, that’s often more disruptive to everyone’s routine.

So veterinarians see dogs with diarrhea much quicker than physicians see their patients with diarrhea.

Another problem with diarrheic dogs is that we are conditioned to “do something.” Veterinarians want to fix the problem, and owners want veterinarians to fix the problem – usually as quickly as possible. When we do something, the diarrhea usually resolves, so we look and feel good about it, and everyone’s happy… BUT did the dog get better because of what we did or despite it?

I’m on a plane back from a ENOVAT meeting where veterinary antimicrobial use guidelines of various sorts were discussed. We have canine acute diarrhea antimicrobial use guidelines coming out soon (more on that later), but first I want to write about a systematic review of antimicrobial and nutraceutical treatment for canine acute diarrhea that was done as part of the guideline development process (Scahill et al, The Veterinary Journal, 2024). 

As with most things in companion animal medicine, the information on this topic available in the scientific literature was pretty sparse and evidence for efficacy of these treatments was often weak. That makes guideline development a challenge, but assessment of the available evidence is critical. The review was structured around several key questions:

Question 1: In dogs with acute diarrhoea, does antimicrobial treatment compared to no antimicrobial treatment have an effect?

The short answer was: not much of one.

The net effect across studies was an overall decrease in duration of diarrhea of 0.28 days with antibiotics, which falls within the “trivial effect” category that was set at the start. So antibiotics seem to have minimal (trivial) benefit in these dogs, but remember that there can also be adverse effects, administration issues and financial costs associated with these treatments.

Below are some figures from the systematic review showing the breakdown of the available evidence:

If we look at duration of hospitalization, the difference between the two groups is still trivial, but this time in favour of the untreated dogs (untreated dogs had 0.37 days shorter duration of hospitalization than antibiotic-treated dogs):

There was no impact of treatment on mortality:

Question 2: In dogs with acute diarrhoea, does metronidazole treatment have a superior effect compared to beta-lactam treatment?

Data were really sparse here, but the conclusion was “Metronidazole does not have a superior effect in comparison to beta-lactams based on the included trials. “

Question 3: In dogs with acute diarrhoea, does long duration (7 days) of antimicrobial treatment have a superior effect compared to short duration (<7 days) of treatment?

There were no studies directly comparing treatment regimens like this. However, duration of treatment data were available from 8 studies. The conclusion was “Diarrhoea resolved in most dogs before antimicrobial treatment was terminated and diarrhoea did not exceed 7 days (mean or median) except in one study (Rudinsky et al., 2022). In most studies, resolution of diarrhoea occurred after 2–5 days, which is a similar duration to dogs that received no antimicrobials.”

Questions 4-6: In dogs with acute diarrhoea, does treatment with probiotics (#4), synbiotics (#5), or prebiotics (#6) compared to no treatment, shorten the duration of diarrhoea?

Data were (you guessed it) limited. There was an effect of probiotics, driven by one study, but it was another trivial effect (resolution of diarrhea 0.68 days earlier with probiotics):

What can we take home from this??

The overall conclusions of this review and analysis were:

  • High certainty evidence showed that antimicrobial treatment did not have a clinically relevant effect on any outcome in dogs with mild or moderate disease. Certainty of evidence was low for dogs with severe disease. Nutraceutical products did not show a clinically significant effect in shortening the duration of diarrhoea (based on very low to moderate certainty evidence). No adverse effects were reported in any of the studies.

More on the antimicrobial use guidelines that have come from this work soon. They’re done, they’ve been presented (some veterinarians reading this might have heard one of us talking about them already) and are out for an expert comment period, but I’ll provide the full story once they’re released.