Review Question - QID 212807

A 54-year-old man comes to the clinic for management of his gastroesophageal reflux disease (GERD). He is currently on cimetidine for his condition and reports that his GERD initially improved. However, following his recent move to Michigan, he is experiencing more frequent episodes of chest pain (4-5 times a week). The pain is described as burning in quality and is concentrated around his epigastric region following food ingestion. It does not radiate anywhere and is alleviated when he takes antacids. A physical examination demonstrates a healthy male with unremarkable findings. He is subsequently prescribed a new medication for control of his symptoms. What is the most likely mechanism of action of this new medication?