PLASMA PHARMACOKINETICS OF RANITIDINE HCL IN FOALS

Plasma pharmacokinetics of ranitidine HCl were investigated after intr avenous (i.v.) and oral (p.o.) administration of drug to six healthy f oals. 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 de termined using normal phase high performance liquid chromatography, Pl asma 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 o f the plot of concentrations of ranitidine HCl vs, time was best descr ibed by a two-exponent equation for two foals; data for the remaining four foals were best described by a three-exponent equation. Mean valu es for model-independent values were: apparent volume of distribution (Vd(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.min(2)/mL; mean res idence time (MRT)= 108.9 min; and clearance (Cl)= 13.3 mL/min.kg. Foll owing 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 fro m the p.o. study include: AUC = 12 6413 ng.min/mL; AUMC = 18 039 825 n g.min(2)/mL; mean absorption time (MAT)= 32.0 min; observed time to ma ximum plasma concentration (T-max)= 57.2 min; maximum observed plasma concentration (C-max)= 635.7 ng/mL; and bioavailability (F) = 38%.