Abstract
Isotope effect which is among problems on the applicability of a drug labeled with deuterium on the benzene ring to the metabolic studies in man was investigated. l-Ephedrine [α-14C, arom. -2H5] or l-ephedrine [α-14C] was subcutaneously injected to rats and rabbits, and the urine excreted during 24 hr after dosing was submitted to the inverse isotope dilution analysis. The urinary excretion of 14C activity in rats or rabbits given the deuterio-compound was not significantly different from that given the protio-compound. No significant difference was observed in the amount of main urinary metabolites (in rabbits, 1-phenyl-1, 2-propanediol and hippuric acid, and in rats, p-hydroxyephedrine) between the deuterio-and the (proti-odrug) except the amount of unchanged ephedrine which was excreted more by rats receiving deuterated ephedrine. The increased excretion of unchanged ephedrine after dosing of the deuterated compound did not seem to be due to deuterium-isotope effect by another experiment using a mixture of l-ephedrine-[α-14C, arom. -2H5] and l-ephedrine [arom. U-3H1].
