Aspects of metabolism of tamoxifen by rat liver microsomes. Identification of a new metabolite: E-1-[4-(2-dimethylaminoethoxy)-phenyl]-1, 2-diphenyl-1-buten-3-ol N-oxide.

Metabolism of tamoxifen N-oxide by phenobarbitone-induced rat liver microsomes gave a major metabolite which was identified as E-1-[4-(2-dimethylaminoethoxy)phenyl]-1, 2-diphenyl-1-buten-3-ol N-oxide (alpha-hydroxytamoxifen N-oxide) by comparison of mass spectral properties with synthetic material. This new metabolite was also formed from tamoxifen. Tamoxifen epoxide was synthesised; its microsomal metabolism gave the corresponding N-oxide. Neither tamoxifen epoxide nor its N-oxide was detected as a product of tamoxifen metabolism.