A 55-year-old woman presents with mild epigastric pain, intermittent heartburn, and regurgitation for two years; and intermittent watery diarrhea for six months. She underwent an upper gastrointestinal endoscopy two months ago, which revealed a duodenal ulcer. All biopsy samples were negative for H. pylori. She was started on oral pantoprazole 40 mg daily for four weeks. When her symptoms did not resolve, this was increased to 120 mg daily. She has been on the same dose since. Her medical and surgical histories are otherwise unremarkable. She is not on any other medications, including over-the-counter formulations, or supplements. Her family history is also unremarkable; in particular, there is no history of kidney stones or malignancies. She does not smoke. She used to have 1 to 2 standard drinks per week; but stopped drinking after the ulcer was detected.