Comparative Trial of the Effect of Ranitidine and Cimetidine on Gastric Secretion in Fasting Patients at Induction of Anaesthesia

A comparative trial of the H2-receptor antagonists, cimetidine and ranitidine, on gastric pH and volume, was conducted in 168 healthy patients coming to elective surgery. The drugs were administered in random fashion either intravenously (ranitidine 50 mg or 100 mg, cimetidine 300 mg or placebo) or orally (ranitidine 150 mg, cimetidine 300 mg or placebo). The patients received the drugs or placebo 45 minutes to five hours before operation. After induction of anaesthesia, a nasogastric tube was passed and the stomach contents were aspirated. The volume and pH were measured. Those patients receiving ranitidine 50 or 100 mg or cimetidine 300 mg intravenously had statistically significantly higher gastric pH compared to those receiving placebo, but up to eight percent of patients has a pH less than 2.5. Oral administration of cimetidine 300 mg or ranitidine 150 mg were also superior when compared to placebo. However, 25 per cent of the patients receiving oral cimetidine had a pH less than 2.5; cimetidine orally was statistically significantly inferior to ranitidine 100 mg given intravenously. We conclude that the intravenous use of either ranitidine or cimetidine is an acceptable method to decrease the acidity of gastric contents before induction of anaesthesia. Orally, ranitidine appears to be a better choice than cimetidine in the doses studied. Both ranitidine and cimetidine need to be given at least 45 minutes before induction of anaesthesia to be effective; therefore the use of these agents to decrease the risk of acid pulmonary aspiration syndrome by no means obviates the need for proper anaesthesia technique during induction of anaesthesia.