In vitro metabolism of propoxyphene in rat liver: reaction of a carbinol metabolite with acetaldehyde.

The metabolism of the analgesic drug propoxyphene (alpha-d-propoxyphene) has been investigated in the rat liver 9,000 X g supernatant fraction. The incubations were analyzed by HPLC. The major metabolite was norpropoxyphene carbinol, obtained through demethylation and ester hydrolysis. The demethylated metabolite of propoxyphene, norpropoxyphene, was also detected. Addition of acetaldehyde to the incubation mixture decreased the metabolism of propoxyphene. Reactions between norpropoxyphene carbinol and acetaldehyde resulted in a fast disappearance of the carbinol and the formation of a reaction product, the significance of which is discussed.