antibiotic-associated diarrhea antibiotic-associated diarrhea antibiotic-associated diarrhea (aad) results from an imbalance in the colonic microbiota caused by antibiotics. microbiotal alteration changes carbohydrate metabolism with decreased short-chain fatty acid absorption and an osmotic diarrhea as a result. another consequence of antibiotic therapy leading to diarrhea is overgrowth of potentially pathogenic organisms such as clostridium difficile. it is defined as frequent loose and watery stools with no other complications.