Description_x000D_ General description_x000D_ 4′-Hydroxydiclofenac is an important metabolite of aceclofenac, seen mainly in rats. It is the important oxidative metabolite found in urine._x000D_ CYP2C9 metabolite of diclofenac._x000D_ Application_x000D_ 4′-Hydroxydiclofenac has been used to investigate the effect of gentiopicroside (GE) on human cytochrome P450 enzymes in vitro. It has also been used as an enzyme marker to study its metabolic activities in different in vitro liver models.