Medications for diarrhea work in various ways to slow down bowel movements, kill bacteria, or reduce inflammation. Common classes include antibiotics and antidiarrheals. Antibiotics like metronidazole (Flagyl) and Bactrim (sulfamethoxazole/trimethoprim), and vancomycin (Firvanq) may be taken orally to treat infections that cause diarrhea. Loperamide (Imodium A-D), is an oral, antidiarrheal medication that can treat diarrhea itself.