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 an overgrowth of potentially pathogenic organisms such as Clostridioides difficile.
[1] Clostridioides difficile, also known more commonly as C. diff, accounts for 10 to 20% of antibiotic-associated diarrhea cases, because the antibiotics administered for the treatment of certain disease processes such as inflammatory colitis also inadvertently kill a large portion of the gut flora, the normal flora that is usually present within the bowel.
With this lower level of "healthy" bacteria present, the overgrowth of C. diff is then responsible "for elaborating the enterotoxin".