Two-dimensional chemical structures of warfarin and brodifacoum. Structures of warfarin (A), a 4-hydroxycoumarin, and brodifacoum (B), which also carries a 4-hydroxycoumarin ring system like warfarin but has a substituted tetrahydronaphthyl side chain in the terminal methyl group. Adapted from the National Center for Biotechnology Information, PubChem Compound Database.^40,41