by John Dillberger, DVM

Reprinted from the September/October 2010 Claymore

I have not written about diarrhea before now because, frankly, the subject is too large and complicated to tackle in a monthly column. That is partly because diarrhea is not a disease in itself, but a symptom of disease. The list of diseases that can have diarrhea as part of the picture would itself fill many pages of this magazine.

Given the plethora of causes for diarrhea, where should an owner or veterinarian begin when presented with a dog having diarrhea? Intuitively, the best chance of ending an episode of diarrhea is to identify the underlying disease and treat it. For that reason, diagnostic tests are often part of the initial response to diarrhea. But while diagnostic tests are often helpful, one can also treat diarrhea directly, without knowing the cause. How a dog responds to treatment can provide a valuable clue to the cause of the diarrhea. This month’s column deals with an example of this approach.

What is Tylosin?

Tylosin is an antibiotic belonging to a family called macrolides, which includes erythromycin. It is used in livestock and poultry—either to treat disease or as a feed additive that increases weight gain and feed efficiency. How Tylosin enhances growth is still unknown, but it may alter the make-up of intestinal bacterial flora in a way that improves nutrient release and absorption during digestion.

Tylosin is not used in human medicine. For veterinary use, it is available as a powder. It also is available as tablets in Europe.

History of Tylosin and Diarrhea

In veterinary school I was taught that Tylosin was for livestock but not pets. Yet in my first year in practice, the older practitioner mentoring me suggested I try Tylosin in a dog with recurring bouts of diarrhea that were not responding to “standard” treatments. I tried it, and it worked.

My mentor’s inspiration for trying Tylosin may have been a 1976 paper by H.J. Van Kruiningen entitled “Clinical Efficacy of Tylosin in Canine Inflammatory Bowel Disease” published in the relatively new Journal of the American Animal Hospital Association. This apparently was the last paper published on the subject for almost 30 years.

More than ten years after my first experience with Tylosin, one of my Deerhounds developed diarrhea at a dog show, and it would not go away despite all the usual sorts of treatment. Worse, other dogs in the household came down with diarrhea, making clear the cause was infectious. Only Tylosin stopped the diarrhea. Since then, I have used Tylosin successfully in other Deerhounds.

Anecdotal reports of similar experiences are numerous. The picture that emerges from these reports is almost miraculous. Generally, dogs respond quickly to Tylosin, often within 24 hours—even dogs that have suffered from diarrhea for years. On the other hand, diarrhea reappears in many dogs within a matter of weeks or months when treatment is discontinued. Some dogs will remain diarrhea-free when treatment is stopped if they are treated for a very long time (months), but some dogs must remain on Tylosin for life. The effectiveness of Tylosin does not diminish over time, even in dogs treated for life. There is no report of undesirable side effects with Tylosin.

Because of this profile, Tylosin may be the most common drug used to treat unspecific intermittent or chronic diarrhea in dogs. And yet, no clinical research on Tylosin-responsive diarrhea in dogs was available until recently, when a group of veterinary researchers in Helsinki, Finland headed by Elias Westermark began studying this “disease.”

Recent studies of Tylosin and Diarrhea

Dr. Westermark’s group has conducted two clinical trials on Tylosin-responsive diarrhea. The first study included 14 adult pet dogs of 12 different breeds that had shown chronic or intermittent diarrhea for more than a year. Each dog had been successfully treated with Tylosin for at least six months, and the treatment had been discontinued at least twice, but the signs had always occurred. When the study started, all dogs had been on Tylosin for at least one month and were otherwise healthy. Thereafter, Tylosin was discontinued, and diarrhea reappeared in 12 dogs (85.7%) within a month. When Tylosin was resumed in these dogs, diarrhea stopped in most dogs within 24 hours and in all dogs within three days. In contrast, prednisone did not completely resolve the diarrhea, and the probiotic Lactobacillus rhamnosus GG did not prevent the relapse of diarrhea in any dog. Diet was not changes in any dog at any time during the study.

In the second study, seven beagles with chronic diarrhea were given Tylosin for ten days. During treatment the feces became firmer but were still unacceptably loose. When Tylosin was stopped, diarrhea reappeared within three weeks. Treatment with metronidazole, trimethoprim-sulfadiazine, doxycycline, or prednisone had almost no effect. The diet was then changed for ten days from moist to dry food. The feces again became firmer, but remained loose in some dogs. Dry food was fed three more months, but fecal consistency continued to fluctuate from ideal to diarrhea. The dogs were then treated a second time with Tylosin for ten days. The feces then became normal and stayed so for three months, until the study ended.

The Typical Picture

Tylosin-responsive diarrhea is most common in middle-aged, large-breed dogs. Diarrhea typically starts as intermittent but becomes more frequent and ends as persistent. Loose fecal consistency is the predominant sign, with owners typically describing the feces as watery and/or mucoid. Owners also often report an increase in gurgling intestinal sounds (borborygmus) and flatulence. Appetite may be lessened, and vomiting is occasionally seen during the diarrheal outbreaks.

Suggested Approach

In a dog with diarrhea, every effort should be made to find the cause. The first steps should be to review the medical history, conduct a thorough physical examination, and do routine blood tests and fecal examinations. If results reveal that the dog’s only problem is diarrhea, then he should be treated with fenbendazole (50 mg/kg) for three days to rule out parasites as a cause for the diarrhea.

If diarrhea continues, then an adverse food reaction should be excluded before trying Tylosin. Opinions vary widely about how the diet should be changed for a dietary treatment trial. Unfortunately, current recommendations are largely based on anecdotal evidence rather than on controlled trials. The most common recommendation is to use a diet with novel protein and carbohydrate sources, with the former restricted to a single animal source.

If modifying the feeding regime does not end the diarrhea, then the next step is to treat the dog with Tylosin at 25 mg/kg once a day. Dogs responding to Tylosin will usually do so within 5 days, and diarrhea will remain absent as long as treatment continues. In many dogs, diarrhea will reappear within weeks if treatment stops. In that case, one can try changing the dog’s diet once again to make sure that the feeding regime is not involved, but if that does not work, then Tylosin should be resumed.

For long-term use, the Tylosin dose should be tapered to the lowest that is effective. Many dogs need only half of the recommended dose, and they may need to be treated only every other day.


Dr. John E. Dillberger, P.O. Box 2118, Nashville, IN 47448-2118 (812) 988-6175