Center of Drug Evaluation Research - Office of Generic Drugs 1 article published in JoVE Medicine Quantification of the Immunosuppressant Tacrolimus on Dried Blood Spots Using LC-MS/MS Touraj Shokati1, Nicholas Bodenberger1, Holly Gadpaille1, Björn Schniedewind1, Alexander A. Vinks2, Wenlei Jiang3, Rita R. Alloway4, Uwe Christians1 1iC42 Clinical Research and Development, University of Colorado, Anschutz Medical Campus, 2 Here we describe a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay to quantify the immunosuppressant tacrolimus in dried blood spots using a simple manual protein precipitation step and online column extraction.