[Stable isotope methodology in the pharmacokinetic study of steroids]

Stable isotopically labeled steroids can, without radiation hazards, be safely used as biological internal standards to perform pharmacokinetic studies of steroids in man. This technique offers an advantage in that an endogenous steroid and its stable isotopically labeled analogue exogenously administered can be differentiated easily by employing mass spectrometry. For example, we can examine the pharmacokinetics of cortisol and investigate the metabolic conversion of cortisol to cortisone in man by administering deuterium-labeled cortisol to human subjects as a tracer. The number and the stability of the label are fundamental requisites in stable isotope methodology. Successful application of methodology with stable isotopes is then always dependent on the availability of compounds that are labeled at predesignated chemically inert positions.