Preoperative cimetidine--effects on gastric fluid

Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures

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Actions of cimetidine and ranitidine at some cholinergic sites: implications in toxicology and anesthesia

Cimetidine and ranitidine are specific and potent H2-receptor antagonists widely used in the effective therapy of peptic ulcer disease. The drugs also possess other pharmacological properties unrelated to H2-receptor antagonism. More recently large experimental doses of cimetidine or ranitidine were found to have anticholinesterase, ganglion blocking and neuromuscular blocking activities. Actions of the drugs at such cholinergic sites may account for some of their clinically documented adverse effects. The toxicological implications of these findings including the potential for drug interactions to occur, especially during some anesthetic procedures, are discussed.

Anticholinesterase activity of and possible ion-channel block by cimetidine, ranitidine and oxmetidine in the toad isolated rectus abdominis muscle

Responses of the toad isolated rectus abdominis muscle to cumulative doses of acetylcholine were recorded in the absence or presence of varying concentrations of cimetidine, ranitidine or oxmetidine. The corresponding cumulative log concentration-response curves for acetylcholine were then plotted for each antagonist studied. Cimetidine (5 mmol/l), ranitidine (1 mmol/l) and oxmetidine (0.02 mmol/l) potentiated the effect of acetylcholine by 4-fold, 2.6-fold and 1.3-fold, respectively. At higher concentrations all three histamine H2-receptor antagonists produced a concentration-dependent and non-parallel shift of the acetylcholine curve to the right of the corresponding control curve accompanied by a depression of the maximal response. The results provide further evidence that the H2-antagonists studied possess anticholinesterase activity and also suggest that the H2-antagonists may produce neuromuscular blockade by ion-channel block. The clinical implications of the results obtained are also discussed.

Cimetidine in anesthesia: does it minimize the complications of acid aspiration?

The use of cimetidine, an H2-receptor antagonist, to minimize the complications of acid aspiration pneumonia is reviewed. Since Mendelson's early description of acid aspiration in 66 obstetrical patients, attempts have been made to decrease gastric acidity by administering perioperative antacids and/or antihistamine drugs such as atropine and glycopyrrolate. In this review of the literature, strict attention is given to study design and subject selection, methods of collecting gastric samples and reporting both pH and volume measurements, and medications taken on admission, given preoperatively, and as anesthetics. Clinical trials evaluating cimetidine alone and compared with other prophylactic regimens were reviewed, detailing the timing, route, and frequency of drug administration. Cimetidine appears to be effective in minimizing complications of acid aspiration since gastric acidity (pH less than 2.5) is a contributing factor in both the morbidity and mortality of this disease state. In general terms, cimetidine 300 mg po 1.5-2.0 h prior to intubation or 45-60 minutes iv before surgery will decrease gastric acidity below the critical level. This effect may be maintained for up to three hours. Perioperative cimetidine administration, to minimize the complications of acid aspiration, appears to be safe in terms of drug-drug interactions and effects on labor, the fetus, and the newborn child.

Pre-operative ranitidine. Effect of a single intravenous dose on pH and volume of gastric aspirate

Ninety-four patients undergoing elective surgery received ranitidine 100 mg or 50 mg intravenously one hour pre-operatively, or acted as controls. A gastric aspirate pH in excess of 2.5 one to two hours after administration was achieved in 93% of patients given 100 mg, 88% of those given 50 mg, and 61% of controls. There were no significant differences in the volumes of gastric aspirate.

Protection against pulmonary acid aspiration with ranitidine. A new histamine H2-receptor antagonist

Ninety patients presenting for elective surgery were randomly divided into three groups A, B and C and studied on a double-blind basis to assess the effects of ranitidine, a new histamine H2 -receptor antagonist and placebo on gastric secretion. Group A received 150 mg ranitidine orally at 2200 hours on the evening before surgery and a further 150 mg 1-2 hours before operation. Group B received 150 mg ranitidine with premedication only, while Group C received a placebo at 2200 hours and again with premedication on the day of surgery. Gastric fluid was aspirated immediately after induction of anaesthesia and the volume and pH of the aspirate measured. Gastric volumes were significantly greater in the placebo group when compared to Group B, but not to Group A. The proportion of patients with pH greater than 2.5 at induction of anaesthesia was 100, 82.3 and 67.9% in Groups A, B and C, respectively. The percentage of patients who had measured gastric volume less than 25 ml or pH greater than 2.5 were Group A--90%, Group B--75.9% and Group C--57%. Thus ranitidine 150 mg orally on the evening before surgery and on the morning prior to anaesthetic induction lowered the mean volume and raised the average pH of gastric content to safe levels in all cases.