When pets develop diarrhea, their owners are often quick to make an appointment with their veterinarian, and those who've experienced previous bouts often expect that antibiotics will be prescribed for the pet. It's based on a belief that antibiotics are the quickest way to resolve the problem. In the past, medications like metronidazole were routinely prescribed for diarrhea. Today, however, we know that antibiotics are often not necessary for treating acute diarrhea and may actually do more harm than good. It’s important for owners to understand why a veterinarian’s plan may not include antibiotics.

Research has shown that most dogs with sudden (acute) diarrhea will improve in about the same amount of time - with or without antibiotics. In studies comparing pets given antibiotics to those given a placebo (no active medication), diarrhea resolved just as quickly in both groups. Other studies have shown that diet change or the administration of probiotics can result in equal or better outcomes than metronidazole in pets with diarrhea. This tells us that many cases of diarrhea are self-limiting and that the body can heal itself with supportive care alone.

The intestinal tract of humans and animals is home to a large population of helpful bacteria, collectively known as the gut microbiome. These bacteria aid digestion, protect against harmful bacteria, and help to maintain a healthy gut lining. Studies show that antibiotics like metronidazole can significantly disturb that balance. Even in healthy dogs, antibiotic use can cause a decrease in beneficial gut bacteria, and these changes can persist for weeks after the course of treatment is completed. So, while the stool may look better after a course of treatment with antibiotics, the gut itself may still be struggling to recover. Outwardly, the pet may appear completely normal, but these changes in the gut microbiome impact the health of the animal in ways that are not necessarily apparent. Studies have shown that, in addition to digestion, a healthy microbiome contributes to immune health, the ability to fight infections, and even brain and behaviorial health.

Antibiotics are certainly warranted if there's a suspicion of a serious infection or sepsis. But, for the majority of pets with acute diarrhea, supportive care measures alone can provide equal or superior outcomes. These other measures include providing fluids (to prevent dehydration), changing the diet, medications to protect the gut lining, and administering probiotics. The bottom line is that, more and more, veterinarians are treating diarrhea without antibiotics and prescribing supportive care measures instead. We now know that antibiotics don’t usually speed recovery of acute diarrhea and they can disrupt gut health. In addition to the effects on individuals, avoiding unnecessary antibiotics (when treating any condition) also helps prevent antibiotic resistance. This approach, which is also part of responsible antibiotic use, impacts more than just the pet - it also protects other animals and humans.