Vivafree centrifugal filters offer fast, accurate separations of free drugs for Therapeutic Drug Monitoring. They have been used successfully for phenytoin1, valproic acid, antibiotics, immunosuppressants and other drugs. Vivafree filters are also being used clinically to separate free hormones such as testosterone and insulin. Separations can be performed as quickly as 20 minutes with high recoveries and excellent reproducibility. Savings of 35% have been reported when switching to Vivafree filters from another centrifugal ultrafiltration device2.