A 60-year-old woman presents with a 6-week history of

A 60-year-old woman presents with a 6-week history of diarrhea. She has had 6 to 8 large-volume watery stools daily. Th ere has been no blood in the stool. She has not had fever or other systemic symptoms. Recently, she has not taken antibiotics or changed medication. Clinical examination fi ndings were normal. Laboratory test results were unremarkable. Stool examination for fecal leukocytes was negative. On colonoscopy, the colon appeared normal. On biopsy, a thickened subepithelial collagen band was apparent. What initial therapy should you recommend?