The stability of amitriptyline N-oxide and clozapine N-oxide on treated and untreated dry blood spot cards

► We discuss the merits of using DBS for discovery PK studies. ► We examine the stability of labile N-oxides on 'treated' and 'untreated' DBS cards. ► Amitryptyline-NO and Clozapine-NO are used as probe compounds. ► Card type was found to significantly affect degradation. ► N-oxide degradation to parent compound enriches parent response.