Bioavailability, distribution and pharmacokinetics of diethystilbestrol produced from stilphostrol

The kinetic behavior of diethylstilbestrol (DES) produced from stilphostrol has been studied in man, dog and rat. A sensitive and selective assay for DES in plasma and tissues has been developed with the use of gas chromatographic separation and mass spectrometric detection. In patients with prostate cancer, the plasma concentrations of DES produced by 1,000-mg. infusions of stilphostrol are 1,500 times the DES concentrations produced by conventional oral DES doses. The pharmacokinetics of DES show 2 separate phases; 1 with a t1/2 of approximately 1 hour, another with a t1/2 of approximately a day. In rats, stilphostrol does not selectively liberate DES in the prostate compared to dosing with DES itself. In dogs, a 50-mg. tablet of stilphostrol was bioequivalent to 40 mg. of DES taken orally. Some of these data support the idea that the high DES concentrations produced by stilphostrol infusions underlie in its ability to produce objective responses in patients refractory to conventional oral DES therapy.