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 fash ion after placement of a gastric electrode for continuous 24-h pH moni toring. In patients receiving omeprazole 20 mg (n = 13) and 40 mg (n = 13), gastric pH greater than or equal to 2.5 was achieved after a med ian 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 (16-8 4) min, respectively (P = NS). Over the first 24 h postoperatively, ga stric 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 (2 40 min vs 780 min) after omeprazole 20 mg than after ranitidine 50 mg. There were no other significant differences among treatment groups re garding 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 t o 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 d ose of ranitidine 25 mg or 50 mg should be administered 30-45 min prio r to induction of anesthesia.