Assay of Secoverine and Active Metabolites: Comparison of Stable Isotope Dilution with Receptor Binding Assay

Secoverine (formula below) is a new gastro-intestinal muscle relaxant whose pharmacokinetics and disposition are currently being investigated in different animal species and man. The drug is administered as a racemate of which only the (+) enantiomer has pharmacological activity. Human pharmacology revealed activity after either oral or parenteral administration. Plasma levels of the parent drug were hardly measurable (<1 ng/ml) after oral administration, whereas a similar i.v. dose resulted in plasma levels of ~10 ng/ml. Accordingly we investigated the occurrence of active metabolites. As urinary metabolite profiles did not provide any clue in this respect, we started in vitro experiments with 14C-labelled secoverine.