Thalidomide is distributed into human semen after oral dosing

As part of a double-blind placebo-controlled study of the effect of thalido mide on body weight and the viral load of human immunodeficiency virus-sero positive patients, plasma and semen samples were analyzed for the presence of thalidomide. Patients were orally dosed with 100 mg of thalidomide/day f or 8 weeks. Blood samples were obtained at baseline and weeks 4, 8, and 12, and semen was obtained at baseline and weeks 4 and 8. Samples were extract ed with solid-phase cartridges and analyzed by liquid chromatography/tandem mass spectrometry using atmospheric pressure chemical ionization in the ne gative ion mode. Two of four patients taking thalidomide were able to provi de semen samples. Both had detectable levels of thalidomide in their plasma (10-350 ng/ml) and semen (10-250 ng/g) at weeks 4 and 8. There was an appa rent correlation between plasma and semen levels. Semen levels could be sig nificantly greater for therapeutic doses of more than 100 mg/day. Since the threshold dose for birth defects and thalidomide exposure is not known, ma le patients are advised to use barrier contraception.