Source: FDA, National Drug Code (US) Revision Year: 2018
Estramustine phosphate (Figure 1) is a molecule combining estradiol and nornitrogen mustard by a carbamate link. The molecule is phosphorylated to make it water soluble.
Figure 1. Estramustine Phosphate:
Estramustine phosphate taken orally is readily dephosphorylated during absorption, and the major metabolites in plasma are estramustine (Figure 2), the estrone analog (Figure 3), estradiol, and estrone.
Figure 2. Estramustine:
Figure 3. Estrone Analog of Estramustine:
Prolonged treatment with estramustine phosphate produces elevated total plasma concentrations of estradiol that fall within ranges similar to the elevated estradiol levels found in prostatic cancer patients given conventional estradiol therapy. Estrogenic effects, as demonstrated by changes in circulating levels of steroids and pituitary hormones, are similar in patients treated with either estramustine phosphate or conventional estradiol.
The metabolic urinary patterns of the estradiol moiety of estramustine phosphate and estradiol itself are very similar, although the metabolites derived from estramustine phosphate are excreted at a slower rate.
Long-term continuous administration of estrogens in certain animal species increases the frequency of carcinomas of the breast and liver. Compounds structurally similar to EMCYT are carcinogenic in mice. Carcinogenic studies of EMCYT have not been conducted in man. Although testing by the Ames method failed to demonstrate mutagenicity for estramustine phosphate sodium, it is known that both estradiol and nitrogen mustard are mutagenic. For this reason and because some patients who had been impotent while on estrogen therapy have regained potency while taking EMCYT, the patient should be advised to use contraceptive measures.
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