A55-year-old man presents to the physician's office complaining of upper abdominal pain of 2 months' duration. The pain is described as gnawing, localized to the upper midline, and associated with nausea. The pain is exacerbated by food, and there is an associated 20-lb weight loss over 2 months. His past history is pertinent for a 30 pack-year smoking history, occasional alcohol intake, and a prior history of a benign gastric ulcer 5 years ago. Physical examination reveals normal vital signs, mild epigastric pain with deep palpation, and mildly hemepositive stool. An evaluation for recurrence of a gastric ulcer is recommended. In this patient, a benign gastric ulcer was found, and he was placed on a proton-pump inhibitor and triple antibiotics for Helicobacter pylori. He returns to the physician's office 3 months later with similar complaints and, on re-evaluation, the gastric ulcer was found to persist.
Which of the following is the most appropriate next step in management?