Snapshot A 40-year-old woman presents to her primary care doctor for diarrhea that started last night. She denies having eaten any bad foods, and no one around her was sick with the same symptoms. However, she did have a meal with raw oysters 2 nights ago but reports that “the restaurant is always so clean.” She reports having recently had a urinary tract infection and is currently taking antibiotics for it. She notes that the diarrhea started soon after starting her antibiotics. Her vital signs are within normal limits and her routine laboratory testing is normal as well. She is started on loperamide. Introduction Drugs loperamide Mechanism of action μ-opioid receptor agonist, which decreases gut motility decreases fecal volume increase viscosity in the gut since it has poor central nervous systemic penetration, there is low concern for addiction Clinical use acute diarrhea (i.e., traveler's diarrhea) Adverse effects constipation nausea dry mouth can have QT prolongation