{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,4]],"date-time":"2026-09-04T20:35:25Z","timestamp":1788554125541,"version":"build-2803163510"},"reference-count":38,"publisher":"Ovid Technologies (Wolters Kluwer Health)","issue":"5","license":[{"start":{"date-parts":[[2025,5,22]],"date-time":"2025-05-22T00:00:00Z","timestamp":1747872000000},"content-version":"unspecified","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"content-domain":{"domain":["lww.com","ovid.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2025,10]]},"abstract":"<jats:sec>\n            <jats:title>Background:<\/jats:title>\n            <jats:p>Therapeutic drug monitoring of immunosuppressants is critical in balancing insufficient immunosuppression due to underdosing, and severe adverse effects due to overdosage. For a more comprehensive therapeutic drug monitoring and follow-up of transplant patients, the aim was to develop a liquid chromatography\u2013tandem mass spectrometry method for the simultaneous quantification of tacrolimus, cyclosporine A, tryptophan, kynurenine, and creatinine using a volumetric absorptive microsampling device.<\/jats:p>\n          <\/jats:sec>\n          <jats:sec>\n            <jats:title>Methods:<\/jats:title>\n            <jats:p>Venous and capillary blood samples were simultaneously collected using a volumetric absorptive microsampling device called Mitra. The method involved protein precipitation followed by offline solid-phase extraction using a positive pressure manifold. Chromatographic separation was achieved by a formic acid\u2013ammonium formate\u2013methanol gradient on a Synergi Polar reversed-phase column. Multiple reaction monitoring in the positive ion mode and stable isotope-labeled internal standards were used for quantification. Validation was performed according to the European Medicines Agency and US Food and Drug Administration (FDA) guidelines.<\/jats:p>\n          <\/jats:sec>\n          <jats:sec>\n            <jats:title>Results:<\/jats:title>\n            <jats:p>Validation was successful, meeting European Medicines Agency and FDA guidelines. Investigation of selectivity, accuracy, and precision met the required criteria of a deviation &lt;15%. Internal standards successfully compensated potential matrix effects. A comparison of 26 anonymized samples from transplant patients on Mitra with venous blood controls demonstrated the method's suitability.<\/jats:p>\n          <\/jats:sec>\n          <jats:sec>\n            <jats:title>Conclusions:<\/jats:title>\n            <jats:p>For the first time, we herein describe a liquid chromatography\u2013tandem mass spectrometry method for the simultaneous quantification of tacrolimus, cyclosporine A, tryptophan, kynurenine, and creatinine on Mitra. Self-collection of samples may facilitate therapeutic monitoring. Simultaneous determination of creatinine may help monitor kidney function, while tryptophan and kynurenine may serve as a biomarker for early detection of transplant rejection.<\/jats:p>\n          <\/jats:sec>","DOI":"10.1097\/ftd.0000000000001341","type":"journal-article","created":{"date-parts":[[2025,5,22]],"date-time":"2025-05-22T09:01:10Z","timestamp":1747904470000},"page":"669-675","update-policy":"https:\/\/doi.org\/10.1097\/lww.0000000000001000","source":"Crossref","is-referenced-by-count":5,"title":["An Offline SPE-LC-MS\/MS Method for Simultaneous Quantification of Tacrolimus, Cyclosporine A, Kynurenine, Tryptophan, and Creatinine Using Volumetric Absorptive Microsampling Device Mitra"],"prefix":"10.1097","volume":"47","author":[{"given":"Kajetan","family":"Nierychlewski","sequence":"first","affiliation":[{"name":"Institute of Laboratory Medicine, LMU University Hospital, LMU Munich, 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