Original Article: PDF OnlyDevelopment and Validation of an LC-MS/MS Method to Simultaneously Measure Tacrolimus and Everolimus Concentrations in Kidney Allograft Biopsies after Kidney TransplantationZhang, Mengyu MSc1,a; Tajima, Soichiro PhD2,a; Shigematsu, Tomohiro BSc1,2; Noguchi, Hiroshi MD, PhD3; Kaku, Keizo MD, PhD3; Tsuchimoto, Akihiro MD, PhD4; Okabe, Yasuhiro MD, PhD3; Egashira, Nobuaki PhD1,2; Ieiri, Ichiro PhD1,2Author Information 1Department of Clinical Pharmacology and Biopharmaceutics, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan 2Department of Pharmacy, Kyushu University Hospital, Fukuoka, Japan 3Department of Surgery and Oncology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan 4Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan Correspondence: Soichiro Tajima, PhD, Department of Pharmacy, Kyushu University Hospital, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Telephone: +81 92 641 1151 E-mail: [email protected] Conflicts of Interest and Source of Funding: The authors declare no conflicts of interest. a These authors contributed equally to this work. Therapeutic Drug Monitoring: June 28, 2021 - Volume - Issue - doi: 10.1097/FTD.0000000000000912 Buy PAP Metrics Abstract Background: Therapeutic drug monitoring (TDM) is necessary for immunosuppressive therapy with tacrolimus and everolimus after kidney transplantation. Several studies have suggested that the concentrations of immunosuppressive agents in allografts may better reflect clinical outcomes than whole blood concentrations. This study aimed to develop a method for the simultaneous quantification of tacrolimus and everolimus concentrations in clinical biopsy samples and investigate their correlation with histopathological findings in kidney transplant recipients. Methods: Fourteen biopsy samples were obtained from kidney transplant recipients at 3 months after transplantation. Kidney allograft concentrations (Ctissue) of tacrolimus and everolimus were measured by liquid chromatography tandem mass spectrometry (LC-MS/MS), and the corresponding whole blood trough concentrations (C0) were obtained from clinical records. Results: The developed method was validated over a concentration range of 0.02[FIGURE DASH]2.0 ng/mL for tacrolimus and 0.04[FIGURE DASH]4.0 ng/mL for everolimus in kidney tissue homogenate. The Ctissue of tacrolimus and everolimus in kidney biopsies ranged from 21.0 to 86.7 pg/mg tissue and 33.5 to 105.0 pg/mg tissue, respectively. Dose-adjusted Ctissue of tacrolimus and everolimus was significantly correlated with the dose-adjusted C0 (P < 0.0001 and P = 0.0479, respectively). No significant association was observed between the Ctissue of tacrolimus and everolimus and the histopathologic outcomes at 3 months after transplantation. Conclusions: This method could support further investigation of the clinical relevance of tacrolimus and everolimus allograft concentrations after kidney transplantation. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.