Effects of single-dose intravenous omeprazole and ranitidine on gastric pH during general anesthesia

We conducted a comparative trial of the gastric proton pump inhibitor omeprazole and the H2-receptor antagonist ranitidine on gastric pH in 50 adult patients scheduled for elective gynecologic surgery. The drugs were administered intravenously in random fashion after induction of general anesthesia and placement of a gastric electrode for continuous pH monitoring. The two drugs caused significant increases in gastric pH that did not differ significantly when compared with one another, yet there were significant differences from the control group, which did not receive either of the two drugs. A gastric pH of 2.5 was reached within median 34 and 26 min after administration of omeprazole (40 and 80 mg, respectively) and within median 32 and 26 min after administration of ranitidine (50 and 100 mg, respectively). After injection of omeprazole, a gastric pH of 3.5 was reached after median 41 and 34 min; injection of ranitidine (50 and 100 mg) produced a pH of 3.5 after median 43 and 48 min, respectively. We conclude that the intravenous administration of a single dose of omeprazole or ranitidine causes a similar increase, both in magnitude and time of onset, in gastric pH during general anesthesia.