Gas chromatography and mass spectrometry of dimethylethylsilyl ether derivatives of norethisterone metabolites in plasma.

Metabolites isolated from human plasma after oral administration of norethisterone were assayed as their novel dimethylethylsilyl ether derivatives by gas chromatography--mass spectrometry--ion selective monitoring. The major metabolite is 3 alpha, 5 alpha-tetrahydronorethisterone. The unchanged drug is present in a measurable amount even after 8 h of drug administration. The method is accurate, precise and highly sensitive.