The effects of intravenous cimetidine and metoclopramide on gastric volume and pH

The effects on gastric pH and volume of intravenous administration of cimetidine and metoclopramide before induction of anesthesia were studied. Sixty ASA Class I patients scheduled for elective surgery were randomly divided into four groups of 15 each, and the study was double-blinded. Group I received normal saline only; Group II received 4 mg/kg of cimetidine only; Group III received 0.15 mg/kg of metoclopramide only; and Group IV received 4 mg/kg of cimetidine and 0.15 mg/kg of metoclopramide. All drugs were given intravenously 30 min before induction of anesthesia. Gastric aspirates were collected during anesthesia, 30 min and 60 min after administration of the drugs. Metoclopramide reduced gastric volume significantly when administered alone (P = 0.0001), but cimetidine did not (P = 0.10). Cimetidine increased the gastric fluid pH significantly (P = 0.0001) as did metoclopramide (P = 0.0023). The effects of cimetidine and metoclopramide on gastric fluid pH were additive when administered together. The combination of cimetidine and metoclopramide when given intravenously before anesthesia provides greater protection against aspiration pneumonitis in patients at risk than does either drug alone.