Plasma pharmacokinetics of ranitidine HCl in foals

Plasma pharmacokinetics of ranitidine HCl were investigated after intravenous (i.v.) and oral (p.o.) administration of drug to six healthy foals. Twelve‐ to sixteen‐week‐old foals received 2.2 mg ranitidine/kg i.v. and 4.4 mg ranitidine/kg p.o. Concentrations of ranitidine were determined using normal phase high performance liquid chromatography. Plasma concentrations of ranitidine HCl declined from a mean of 3266 ng/mL at 5 min to 11 ng/mL at 720 min 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: apparent volume of distribution (Vdss) = 1.46 L/kg; area under the curve (AUC) = 16 7442 ng·min/mL; area under the moment curve (AUMC) = 18 068 221 ng·min2/mL; mean residence time (MRT) = 108.9 min; and clearance (Cl) = 13.3 mL/min.kg. Following p.o. administration, a two‐exponent equation best described data for five foals; data for the remaining foal were best described by a three‐exponent equation. Mean values of the pharmacokinetic values from the p.o. study include: AUC = 12 6413 ng·min/mL; AUMC = 18 039 825 ng·min2/mL; mean absorption time (MAT) = 32.0 min; observed time to maximum plasma concentration (Tmax) = 57.2 min; maximum observed plasma concentration (Cmax) = 635.7 ng/mL; and bioavailability (F) = 38%.