Vivafree centrifugal filters from Vivaproducts separate free drugs and hormones from those that are bound to plasma proteins. Used for therapeutic drug monitoring of phenytoin, immunosuppressants, and antibiotics, Vivafree filters have also been used for clinical testing of free testosterone and free insulin samples. Separations are achieved in 15-20 minutes with high recovery of the free drug or hormone. Final analysis has been performed by immunoassay as well as by liquid chromatography/mass spectrometry.