Intra-arterial administration of hexobarbital enantiomers to the rat: disposition and estimation of apparent extraction ratio

The enantiomers of hexobarbital, designated as S(+)-HB and R(-)-HB, were administered intra-arterially to rats in a dose of 25 mg X kg-1. Blood pharmacokinetics of the parent compound and two metabolites as well as urinary excretion of three major metabolites were studied. Using previously obtained data following oral administration of S(+)-HB and R(-)-HB two different methods for calculation of the hepatic extraction ratio (E) were compared. The metabolite profile in the urine after intra-arterial administration was not basically different from corresponding data on oral administration. The clearance of low-dose, intra-arterially administered S(+)-HB is useful as an indicator of hepatic blood flow in the rat.