Lessons from prolonged gastric pH monitoring.

Intragastric pH monitoring has shown that the distribution of acidity within the stomach is not homogeneous. Not only is it affected by meals but it also has a circadian rhythm in which nocturnal pH falls to very acid levels in normal subjects. Although results of pH monitoring are highly reproducible within individuals, considerable inter-individual variation has been shown. Duodenal ulcer patients do not appear to possess the normal buffering reaction to meals, but their night-time acidity is within the normal range. In these patients, antacids and pirenzepine have a small acid-neutralizing effect in the stomach; cimetidine is less potent than ranitidine and famotidine. Clinicians can choose between a single dose of either ranitidine or famotidine in the evening with dinner and a twice-daily regimen.