Pharmacokinetics and testosterone suppression of a single dose of polyestradiol phosphate (Estradurin®) in prostatic cancer patients

The pharmacokinetics and endocrine effects of polyestradiol phosphate (PEP; Estradurin) were studied by determination of the concentrations of estradiol (E2), unconjugated (E1) and total estrone (tE1; > or = 85% estrone sulfate), and testosterone in serum from 11 prostatic cancer patients after administration of a single intramuscular injection (320 mg). After injection of PEP, serum concentrations of E2, E1, and tE1 increased during 2-3 weeks. Thereafter serum E2 declined monophasically with a mean half-life of 70 days. The elimination of E1 and tE1 seemed to be governed by the formation of E2. The testosterone concentration decreased inversely to the raising E2 level and reached castration levels within 3 weeks and remained at this level for about 2 weeks, whereafter it increased inversely to the decreasing E2 concentrations.