New Results on the Pharmacokinetics of Fosfestrol

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Abstract
For more than 30 years Fosfestrol (Honvan®) has been used as an estrogen for successful palliative therapy of prostatic carcinoma, but the pharmacokinetics of this compound were unknown due to the lack of analytical methods. Over the last few years we have developed a special extraction process for Fosfestrol and its metabolites from plasma with recovery yields > 90%. The simultaneous measurement of the most important compounds after intravenous and oral administration was achieved by high-performance liquid chromatography, either with the UV detector (236 nm) or with an electrochemical detector (+ 1 V). The working electrode is a carbon paste electrode constructed in this laboratory; the counter electrode is an Au and the reference electrode an Ag/AgCl electrode. The electrode processes have been clarified. Fosfestrol and its monophosphate exist only for a short time in small amounts in the circulating blood after intravenous administration, whilst after oral administration, not even traces of the phosphates could be detected in the plasma. The most important influence on plasma levels of Fosfestrol and its metabolites is due to the extraction function of the liver. Diethylstilbestrol conjugates enter into the enterohepatic circle, thus forming a possible source of DES available over more than 24 h. Only DES glucuronide and DES glucuronide-sulphate are renally eliminated and could be detected after administration over 3 days.

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