Binding of Toremifene to Human Serum Proteins

: The in vitro protein binding of toremifene in human serum was measured by ultracentrifugation using 3H‐toremifene together with unlabeled toremifene, 50, 500, and 5000 ng/ml. Of the total radioactivity 99.7 per cent was bound to the proteins independent of the concentration of the unlabeled drug. Binding of toremifene to different protein fractions was studied by adding 3H‐toremifene and 500 ng/ml of cold toremifene to normal serum. The serum samples were exposed to agarose gel electrophoresis to fractionate different proteins. The radioactivity was localized using a position‐sensitive proportional counter. After that the proteins were visualized by staining. Of the total protein bound radioactivity 92 per cent was bound to albumin, about 6 per cent to β1 globulin fraction and about 2 per cent to a fraction between albumin and α1 globulins, part of this probably to α1 acid glycoprotein.