A 45-year-old man with a history of dyspepsia underwent upper endoscopy, which revealed a gastric ulcer. Biopsies confirmed the presence of Helicobacter pylori infection. He was treated with 14 days of quadruple therapy, including bismuth subsalicylate, metronidazole, tetracycline, and a proton-pump inhibitor (PPI). He completed therapy 5 days ago and is currently asymptomatic. What is the most appropriate next step in management?
