MS-1374

A man in his early 50s arrives at the Emergency Department complaining of abdominal pain and haematemesis. Upon diagnosis, he is found to have a peptic ulcer. During his treatment, he reveals that he has been taking ibuprofen for several years. His physician informs him that this may have caused the bleeding and recommends taking omeprazole, a gastroprotective medication, in addition to his ibuprofen to lower his chances of recurrence. What is the mechanism of action of omeprazole?