Metabolism of estramustine phosphate (Estracyt) in patients with prostatic carcinoma

Plasma samples from patients with prostatic cancer under oral treatment with estramustine phosphate (Estracyt) were quantitatively analyzed for the presence of the parent drug and some of its possible metabolites. Specific methods based on radioimmunoassay and gas chromatography-mass fragmentography were used. Dephosphorylation and oxidation at the 17-position of estradiol were shown to be the major metabolic routes. The estrone analogue of estramustine was found to be the main metabolite in plasma. Elevated levels of estradiol and estrone showed that hydrolysis of the carbamic ester also occurred in these patients. Their estrogen levels were compared with those of another group of prostatic cancer patients receiving conventional hormonal therapy, polyestradiol phosphate (Estradurin). Similar concentrations of estradiol were found in the two groups but the concentrations of estrone were higher in patients given estramustine phosphate.