Dose-response effects of intravenous ranitidine on gastric pH and volume in outpatients.

The dose-response effects of intravenous ranitidine given 45 min to 5 h earlier on gastric pH and volume were evaluated in six groups of 25 outpatients, each undergoing elective surgery under general anesthesia. Patients in Group 1 received no ranitidine and served as controls. Patients in Groups 2-6 received ranitidine intravenously in incremental doses of 0.5 mg X kg-1 body weight from 0.5 mg to 2.5 mg (Group 2, 0.5 mg; Group 3, 1.0 mg; Group 4, 1.5 mg; Group 5, 2.0 mg; and Group 6, 2.5 mg). Ninety-six per cent of patients in the control group (Group 1) had gastric pH less than or equal to 2.5 while 36% of the patients had gastric content volumes greater than or equal to 25 ml with pH less than or equal to 2.5. Ranitidine, in incremental doses of 05.-2.5 mg X kg-1 body weight, caused a significant reduction of gastric acidity and volume. The ED50 of ranitidine producing a gastric pH greater than 2.5 was 0.36 mg X kg-1, and the ED95 was 0.98 mg X kg-1 body weight. The ED95 of ranitidine producing a gastric volume less than 25 ml was 1.96 mg X kg-1. At the dose of 1.5 mg X kg-1 of ranitidine, 100% of the patients had gastric contents with pH greater than 2.5. The proportion of patients with volume less than 25 ml was 68% with ranitidine, 0.5 mg X kg-1, and gradually increased to 100% with 2.5 mg X kg-1 body weight.(ABSTRACT TRUNCATED AT 250 WORDS)