Helicobactoer pylori affects the magnitude of acid inhibition by proton pump inhibitors.1-3 In an early study, omeprazole produced greater acid suppression in subjects with H pylori infection than in those without infection.1Direct evidence of the interaction between H pylori infection and the efficacy of omeprazole came from studies in which cure of the infection resulted in a decrease in the antisecretory effect exerted by omeprazole, both in healthy subjects2 and in patients with duodenal ulcer disease.3

In this issue (see page 468) Gillen et al confirm the effect of H pylori on the reduction in acidity produced by omeprazole. The authors have tried to elucidate the mechanism responsible for this effect. They report data which seem to refute the previously postulated hypothesis1-3 that ammonia is important in the interaction between H pylori and omeprazole.

Nevertheless, there are many good reasons favouring the ammonia buffering system hypothesis. Firstly, this theory takes into account the equilibrium between secreted protons and ammonia produced by H pylori. The ammonia buffering system has a minimal apparent effect in the absence of omeprazole therapy when the H⁺ concentrations in the stomach are high, but it becomes effective …