Effect of a 2 g cimetidine infusion on twenty-four-hour intragastric pH in critically ill patients.

We evaluated the effect of a cimetidine continuous infusion (2 g in 24 h) on the intragastric pH of 16 critically ill patients (11 men, 5 women, mean age 45 years). During the 24 h pre-trial period and the subsequent 24 h cimetidine infusion, an intragastric combined electrode was placed in the fundus and the pH recorded with a portable pH module and data collection unit. In each patient, the cimetidine infusion induced a prolonged rise of intragastric pH. For all patients the mean percentage of readings above pH 4.0 was 11% pre-trial and 75% during the cimetidine 24 h infusion (p less than 0.001). The percentages of readings above 5.0, 6.0, 7.0 were also significantly higher during infusion than pre-trial in the 16 patients. After starting the cimetidine infusion, there was a concomitant rise of median plasma cimetidine and median intragastric pH in the 7 patients studied. After 6 h, median plasma cimetidine remained above 1 mcg/ml. These results and recent data from the literature suggest that in critically ill patients a continuous infusion of cimetidine might prevent stress ulcerations better than bolus injections by maintaining intragastric pH above 4.0 during longer time intervals.