Arachidonic acid is converted by microsomal CYP450 enzymes to a variety of epoxides, ω-1 and ω-hydroxylated compounds via what is known as the epoxidase pathway. MS-PPOH is a selective inhibitor of the epoxygenation reactions catalyzed by specific CYP450 isozymes. MS-PPOH inhibits the formation of arachidonate 11,12-epoxides by CYP4A2 and CYP4A3 enzymes with an IC50 value of 13 µM, but has no effect on the formation of 20-HETE, the ω-hydroxylation product of CYP4A1.