A patient develops gastrointestinal upset (diarrhea/colitis) after taking an antibiotic. Which agent is the most likely cause?

Clindamycin is the classic antibiotic precipitant of antibiotic-associated diarrhea and C. difficile colitis.Other options: Cephalexin, amoxicillin, and azithromycin can cause GI upset but are less classically linked to severe colitis than clindamycin.Key exam takeaway: Clindamycin = high-risk for antibiotic-associated GI/colitis complications.