Studies on drug metabolism by use of isotopes. XXVIII--Biological isotope effect for deuterated ephedrine.

The stability of the deuterium label and the occurrence of an isotope effect for deuterated (-)-ephedrine during metabolic processes were investigated. Determination of the deuterium content in deuterated (-)-ephedrine and its metabolites excreted into urine showed that little, if any, deuterium exchange had occurred. In rats, a slight isotope effect was observed for p-hydroxylation (about 15%) and glucuronide formation of p-hydroxyephedrine and/or its enzymatic hydrolysis (about 20%). In human subjects, there was about 15% difference in the excretion of norephedrine between deuterated and non-deuterated species.