Formation of reductive metabolite, 2-sulfamoylacetylphenol, from zonisamide in rat liver microsomes

Zonisamide (1,2-benzisoxazole-3-methanesulfonamide) was metabolized to its reductive product, 2-sulfamoylacetylphenol, in rat liver microsomes under anaerobic conditions. The rate of NADPH-dependent reaction was much more rapid than that of NADH-dependent reaction. Furthermore, synergistic effect of NADH on NADPH-dependent reaction was not observed. The optimal formation of 2-sulfamoylacetylphenol from zonisamide in the presence of NADPH was observed around pH 7.0. Cimetidine showed an inhibitory effect on the formation of 2-sulfamoylacetylphenol in a dose-dependent manner