Review Question - QID 211061

A 55-year-old man presents to his primary care physician for diarrhea. He has experienced roughly 10 episodes of non-bloody and watery diarrhea every day for the past 3 days. The patient has a medical history of IV drug abuse and recently completed treatment for an abscess with cellulitis. His temperature is 98.7°F (37°C), blood pressure is 107/58 mmHg, pulse is 105/min, respirations are 11/min, and oxygen saturation is 98% on room air. Physical exam reveals diffuse abdominal discomfort with palpation but no focal tenderness. A rectal exam is within normal limits and is Guaiac negative. A CT scan of the abdomen and pelvis is unremarkable. The white blood cell count is 25,000 cells/uL. Which of the following is the most appropriate initial treatment for this patient?