The Effect of Ammonia on Omeprazole-induced Reduction of Gastric Acidity in Subjects with Helicobacter Pylori Infection

Objective: Omeprazole produces a higher intragastric pH during Helicobacter pylori (H. pylori) infection than after cure. We tested the hypothesis that this difference is due to the production of ammonia by H. pylori.

Methods: Gastric acidity and acid output (AO) were measured overnight in 12 subjects, with and without omeprazole, before and 1 and 6 months after cure of H. pylori infection. Gastric ammonia ([NH3]), total bile acid ([TBA]) and protein concentrations and plasma omeprazole levels were measured.

Results: During omeprazole, median AO were 0.0 mmol/h before, 0.86 mmol/h (p = 0.003 vs before cure) at 1 month, and 0.34 mmol/h (p = 0.02) at 6 months after cure; median NH3 output was 0.17 mmol/h before, 0.03 mmol/h (p = 0.002) at 1 month, and 0.02 mmol/h (p = 0.005) at 6 months after cure. AO and NH3 output were similar 1 and 6 months after cure. When corrected for [NH3], AO and gastric pH curves were similar before and after cure. Omeprazole plasma levels increased after cure and gastric [TBA] were unchanged.

Conclusions: The higher pH observed before cure of H. pylori during omeprazole administration is attributable, in large part, to ammonia production. Other acid-neutralizing substances and changes in acid secretion may also be important, but duodenogastric reflux and omeprazole pharmacokinetics are not involved.