Plasma Concentrations of Estradiol and Testosterone in Single-Drug Polyestradiol Phosphate Therapy for Prostatic Cancer

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Abstract
To evaluate the appropriate dosage of polyestradiol phosphate (PEP, Estradurin®) as single-drug therapy, patients with metastatic prostatic carcinoma were given 80, 160 or 240 mg PEP every 4 weeks for at least 6 months. Injection of PEP was followed by rising plasma concentrations of estradiol in the first 2 weeks and slight fall in the next 2 weeks. Testosterone levels fell rapidly in the first 7 days and rose slightly in the following 3 weeks. Steady-state levels were reached after 2 months at the two lowest doses and after 4 months at the highest dose. Steady-state estradiol values increased in linear proportion to the dose. The steady-state concentrations of testosterone were about 45, 25 and 15% of the pretreatment values in the respective groups. At least 160 mg PEP at 4-week intervals is appropriate when the drug is used alone.