Estromustine

Abstract: The pharmacokinetics of estramustine phosphate (EMP) was studied in five prostatic cancer patients given single i.v. and oral doses of EMP in a cross-over study. Plasma and urinary concentrations of parent drug, estramustine, estromustine (the estrone analogue), estradiol and estrone were followed for 32 h. The elimination of intravenous EMP from plasma was biphasic. The mean volumes of distribution were small, being 43 and 108 ml/kg for the central and peripheral compartments, respectively. The plasma clearance was 64 ml/kg/h, and the half-lives of the two phases were 0.16 and 1.27 h. Metabolism was the major route of elimination of EMP. It was readily dephosphorylated and oxidized to yield the cytotoxic metabolites estramustine and estromustine. Estromustine was the main metabolite in plasma. When given orally EMP underwent extensive presystemic dephosphorylation, which started in the gastrointestinal tract. The relative bioavailability of estromustine after administration of EMP-capsules was 44%, which reflects incomplete absorption of EMP rather than first-pass metabolism of estromustine. The terminal half-life of estromustine was 10–20 h, which suggests that EMP might be given once or twice a day.

Abstract: .Plasma concentrations of estramustine phosphate and its major metabolites were measured in patients with prostatic carcinoma treated with increasing oral doses, 70-560 mg/day, of estramustine phosphate (Es-tracyt®). Parent drug and estradiol were measured by radioimmunoassay, and estramustine and its estrone analogue (Leo 271) utilizing gas chromatography. The concentrations of estramustine phosphate and estramustine were below or close to the limits of the methods. A linear correlation was found between the daily dose of estramustine phosphate, and plasma concentrations of Leo 271—the main metabolite—and estradiol, which suggests that no capacity limiting processes are involved in the pharmacokinetics of estramustine phosphate in man. Plasma was also analyzed during prolonged treatment with 560 mg/day. The metabolite pattern was not changed by two to three years of estramustine phosphate treatment.

Abstract: The effect of milk and food on the pharmacokinetics of estramustine phosphate was investigated in six patients with prostatic cancer. In a randomized three-way cross-over study, the patients were given single doses of the drug together with low calcium water, low calcium food and milk. The evaluation was based upon the plasma concentration of two metabolites, estromustine and estrone, as parent drug could not be detected in plasma. The tmax and lag time of estromustine were significantly increased by milk and food intake and Cmax and AUC were significantly decreased. In comparison with water, the AUC of estromustine was 41% when the drug was taken with milk and 67% after simultaneous intake of standardized food. Corresponding figures for the peak values were 32 and 57%, respectively. The effect of milk and food intake on the pharmacokinetics of estrone was similar. Studies in vitro demonstrated that the dissolution of estramustine phosphate disodium was markedly impaired in the presence of calcium. It was concluded that the rate and extent of absorption of estramustine phosphate were decreased when the drug was taken with milk or food due to the formation of a poorly absorbable calcium complex. To obtain high and reproducible absorption of Estracyt, the drug should not be taken together with milk, milk products or other calcium-rich food or drugs.