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 ( V d_ss) = 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 ( T _max) = 57.2 min; maximum observed plasma concentration ( C _max) = 635.7 ng/mL; and bioavailability ( F ) = 38%.