A study sought to evaluate gastric fluid acidity in ambulatory surgical patients 30-120 min after administration of a 300 mg tablet of ranitidine.

20-120 min prior to outpatient surgery, 112 adults with ASA physical status I-III, with no increased risk factors for aspiration of acidic gastric contents, were administered ranitidine with 15 mL of water. After induction of general endotracheal anesthesia, gastric fluid was aspirated. Volume and pH were compared with a reference group of 161 patients (pH = 1.6 + 1) who were not given an H2-antagonist or water.

• Among 40 patients sampled at 30-60 min after drug administration, 26 had pH >5.
• The mean pH was 3.9 +
• After 90 min, 28 out of 28 patients had a pH >5, with a mean pH of 6.3 + 1.
• There was no significant difference with regard to mean gastric volume.

To conclude, in patients with no additional risk factors, oral ranitidine prevented acid production when administered over 90 min prior to induction of anesthesia for outpatient surgery.

Source: Jacobs BR, Swift CA, Dubow GD, et al. Time required for oral ranitidine to decrease gastric fluid acidity. Anesth Analg. 1991;73(6):787-9.