Pharmacokinetics of ranitidine in a homogeneous population of intensive care unit patients during intermittent and continuous administration.

The pharmacokinetics of ranitidine during two different modes of intravenous administration was studied in a homogeneous group of postoperative intensive care unit patients (n = 18). Patients at risk of developing stress-related lesions were randomized to receive repeated injections, 50 mg every 6 h (group A), or a continuous infusion, 50-mg bolus followed by 0.125 mg/kg/h (group B). Before treatment all patients received a single 50-mg ranitidine dose. Serum ranitidine concentrations were measured for 12 h after the single dose and during the treatment period, to calculate individual pharmacokinetic variables. From the single-dose study the calculated half-life, volume of distribution, and clearance were 3.14 +/- 0.61 h, 1.45 +/- 0.42 l/kg, and 0.40 +/- 0.14 l/kg/h for group A and 3.33 +/- 1.08 h, 1.16 +/- 0.20 l/kg, and 0.35 +/- 0.21 l/kg/h, for group B, respectively. Ranitidine pharmacokinetics after the single dose was comparable in the two groups. No statistically significant differences could be detected between the ranitidine pharmacokinetics after the first single dose and the multiple dose or continuous infusion.