Plasma concentrations of estradiol and testosterone in single-drug polyestradiol phosphate therapy for prostatic...

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.