The time course of gastric pH changes induced by omeprazole and ranitidine: a 24-hour dose-response study

The time-course of the effects of single-dose acid-reducing therapy in surgical patients is not known. Therefore, a prospective, randomized trial compared the effects of single-dose administration of omeprazole or ranitidine on gastric pH in 52 patients undergoing lower abdominal surgery. The two drugs were administered intravenously in random fashion after placement of a gastric electrode for continuous 24-h pH monitoring In patients receiving omeprazole 20 mg (n = 13) and 40 mg (n = 13), gastric pH > or = 2.5 was achieved after a median of 80 (range 15-269) min and 40 (6-102) min (P = not significant [NS]), whereas in those receiving ranitidine 25 mg (n = 13) and 50 mg (n = 13), this pH was reached after a median of 32 (15-82) and 44 (16-84) min, respectively (P = NS). Over the first 24 h postoperatively, gastric pH remained less than 2.5 for a significantly longer time (1060 min vs 611 min), and more than 4.0 for a significantly shorter time (240 min vs 780 min) after omeprazole 20 mg than after ranitidine 50 mg. There were no other significant differences among treatment groups regarding the duration of gastric pH less than 2.5, between 2.5 and 4.0, and more than 4.0. In all treatment groups, the gastric pH returned to the baseline value of < 2.0 within 18 h. We conclude that when it is desired that gastric pH be more than 4.0 for at least 3 h, a single dose of ranitidine 25 mg or 50 mg should be administered 30-45 min prior to induction of anesthesia.