ObjectivesTo compare the effects of intermittent intravenous administration and continuous intravenous infusion of famotidine on gastric pH in critically ill patients.DesignA prospective, randomized, crossover study of continuous infusion and bolus administration of famotidine in critically ill patients.SettingA 14-bed medical intensive care unit (ICU) of a 500-bed county hospital.PatientsMedical ICU patients requiring stress ulcer prophylaxis.InterventionsPatients were randomized to receive an equivalent dose of famotidine by continuous infusion or intravenous bolus for 24 hrs, and then were crossed over to the other arm of the study.Measurements and Main Resultsor=to4 over a longer time period than bolus administration (20.8 hrs vs. 12.6 hrs, respectively; p < .01). Onset of therapeutic gastric pH for continuous infusion was slightly delayed as compared with bolus administration.ConclusionsContinuous infusion of famotidine is more effective than an equivalent dose given by intermittent bolus in maintaining the appropriate gastric pH necessary for prevention of stress ulceration. Delayed onset of effect may warrant a priming dose when famotidine is given by continuous infusion.(Crit Care Med 1995; 23:687-691)