Antibiotic-associated diarrhea is a side effect of taking antibiotics. Most often the diarrhea is mild and goes away when you stop taking the antibiotic. Much less common is a very serious type of antibiotic-associated diarrhea called pseudomembranous colitis.
Antibiotics can upset the natural balance of bacteria in the intestines.
When potentially harmful bacteria multiply beyond normal levels in the intestines, diarrhea and other symptoms may result. Almost any antibiotic can cause an imbalance of bacteria in the body. Some of the most common ones include ampicillin and clindamycin. When there is an overgrowth of the bacteria called Clostridium difficile, toxins may be produced that cause severe abdominal pain, fever, and, rarely, bloody diarrhea. This condition is called pseudomembranous colitis.