High-performance liquid chromatographic analysis of tamoxifen, toremifene and their major human metabolites.

The chromatographic behaviour of tamoxifen, toremifene and their major metabolites was investigated by reversed-phase high-performance liquid chromatography on four stationary phases. Two packings were the usual octadecylsilane type and the other two were octylsilane and octadecylsilane of the type specific for basic compounds. The results provide new insight into variations in selectivity with column type for drugs whose basic properties, owing to the presence of an ionizable nitrogen atom, make their chromatography difficult. The results allow an improvement of the separation of metabolites of tamoxifen and toremifene, two triphenylethylene drugs widely used for the treatment of breast cancer. A method is described for the identification and determination of metabolites formed by incubating the parent drugs with human liver microsomal preparations. The assay has been optimized for the identification and quantification of three major metabolites formed by N-oxidative demethylation of the side-chain, 4-hydroxylation of the aromatic ring and a side-chain deamination followed by hydroxylation. These catalytic activities involve cytochrome P450 enzymes.