Antibiotic-Responsive Diarrhea in Small Animals

Chronic diarrhea in dogs for which no underlying cause can be found and which is completely responsive to antibiotic treatment historically was termed small intestinal bacterial overgrowth (SIBO). This name implied that the pathogenesis of the condition depended on the number of bacteria in the small intestine. However, given subsequent concerns about whether a true overgrowth (ie, increased bacterial numbers) exists in dogs, the preferred alternative name of antibiotic-responsive diarrhea (ARD) has been recommended. Idiopathic SIBO is recognized in humans as a true syndrome, particularly in children. However, studies suggest that the overgrowth develops in pockets of fluid between annular mucosal folds found in the human small intestine, and these anatomic structures are not seen in dogs or cats. Thus, although the existence of SIBO in humans is accepted, the subject remains controversial in small animal gastroenterology, with no clear understanding of why and how the condition develops, or exactly why it is antibiotic-responsive. Through a series of questions and answers, this article explores the current evidence and the existing areas of controversy concerning ARD.