A 52-year-old man with a 10-year history of GERD presents with persistent epigastric pain and regurgitation despite taking ranitidine 300 mg twice daily for the past 6 months. Upper endoscopy reveals a 2 cm ulcer in the gastric antrum with no evidence of malignancy on biopsy. H. pylori serology is negative. What is the most appropriate next step in management?