Pharmacokinetics of ranitidine HCL in horses and foals

Abstract

Plasma pharmacokinetics of ranitidine HCl were investigated after intravenous (IV) and oral (PO) administration of drug to six healthy adult horses and six healthy foals. Concentrations of ranitidine were determined using normal phase high performance liquid chromatography. Adult horses received 2.2 mg/kg ranitidine PO and IV. Twelve-to sixteen-week-old foals received 2.2 mg ranitidine/kg IV and 4.4 mg ranitidine/kg PO. In adult horses, plasma concentrations of ranitidine HCl declined from a mean of 5,175 ng/ml at 5 minutes to 37 ng/ml at 720 minutes after intravenous administration. A three-exponent equation, [] best described data for all horses. Mean values for model-independent values calculated from the last quantifiable time point were: Vdss, 1.07 L/kg; AUC, 231,126 ng-min/ml; AUMC, 26,970,792 ng-min2/ml; MRT, 112.6 min; and Cl, 9.8 ml/min/kg. Following PO administration, a two-exponent equation, [] best described the data for five horses; data for the remaining horse were best described by a three-exponent equation. Mean values of pharmacokinetic values from the PO study include: AUC, 59,916 ng-min/ml; AUMC, 10,617,263 ng-min2/ml; MAT, 58.9 min; Tmax, 99.2 min; Cmax, 237.2 ng/ml; and F, 27%. In foals, concentrations of ranitidine HCl declined from a mean of 3,266 ng/ml at 5 minutes to 11 ng/ml at 720 minutes after administration. The profile of the plot of concentrations of ranitidine HCl vs. time was best described by a two-exponent equation for two foals; data for the remaining four foals were best described by a three-exponent equation. Mean values for model-independent values were: Vdss, 1.46 L/kg; AUC, 167,442 ng-min/ml; AUMC, 18,068,221 ng-min/ml; MRT, 108.9 min; and Cl, 13.3 ml/min/kg. Following PO administration, a two-exponent equation, [], best described date for five foals; data for the remaining foal were best described by a three-exponent equation. Mean values of the pharmacokinetic values from the PO study include: AUC, 126,413 ng-min/ml; AUMC, 18,038,825 ng-min2/ml; MAT, 32.0 min; Tmax, 57.2 min; Cmax, 635.7 ng/ml; and F, 38%.