{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,25]],"date-time":"2026-09-25T19:51:33Z","timestamp":1790365893253,"version":"4.1.0"},"reference-count":40,"publisher":"Oxford University Press (OUP)","issue":"3","license":[{"start":{"date-parts":[[2025,1,31]],"date-time":"2025-01-31T00:00:00Z","timestamp":1738281600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/pages\/standard-publication-reuse-rights"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2025,5,2]]},"abstract":"Abstract<\/jats:title>\n \n Background<\/jats:title>\n Therapeutic drug monitoring of the immunosuppressant tacrolimus is commonly performed by immunoassay or LC-MS\/MS. Measurement biases between these methodologies have been characterized for immediate-release tacrolimus (IR-tac; Prograf) but have not been performed for extended-release formulations such as Envarsus. These discrepancies can impact patient care, as appropriate dosing is required to maintain therapeutic concentrations and immunosuppression.<\/jats:p>\n <\/jats:sec>\n \n Methods<\/jats:title>\n Validation of a whole-blood LC-MS\/MS method for the simultaneous quantification of tacrolimus and its major metabolite, desmethyl tacrolimus, was performed using traceable calibrators (tacrolimus, ERM-DA110a) and quality control (QC) material for tacrolimus and standard material for desmethyl tacrolimus. Tacrolimus concentrations were determined by LC-MS\/MS and the ARCHITECT immunoassay in patients receiving either IR-tac or Envarsus for clinical care.<\/jats:p>\n <\/jats:sec>\n \n Results<\/jats:title>\n External calibration curves for both tacrolimus and desmethyl tacrolimus were linear (R2 &gt; 0.995), and the analytical measurement range (AMR) for tacrolimus spanned from 1.1 to 31.6\u2005ng\/mL. Calibrator\/QC biases were within 15% of their spiked concentrations throughout the AMR, and within-run imprecision was &lt;10%, except at the lower limit of quantification (n = 25). Between-run imprecision for low, mid, and high QC levels was \u226411% over a 2-week period (n = 5 days). Comparative biases between immunoassay and LC-MS\/MS were significantly lower (P = 0.0074) for patients receiving Envarsus (n = 20 specimens) relative to patients receiving IR-tac (n = 32 specimens).<\/jats:p>\n <\/jats:sec>\n \n Conclusions<\/jats:title>\n Biases between immunoassay and LC-MS\/MS tacrolimus measurements in patients receiving immediate-release vs extended-release formulations indicate that their distinct pharmacokinetic profiles impact measurement accuracy. These assay biases should be considered when interpreting tacrolimus concentration measurements.<\/jats:p>\n <\/jats:sec>","DOI":"10.1093\/jalm\/jfae156","type":"journal-article","created":{"date-parts":[[2025,1,31]],"date-time":"2025-01-31T12:43:22Z","timestamp":1738327402000},"page":"546-558","source":"Crossref","is-referenced-by-count":3,"title":["Measurement of Whole Blood Tacrolimus Concentrations by LC-MS\/MS and Immunoassay Methods: Influence of Immediate-Release vs Extended-Release Tacrolimus Formulations"],"prefix":"10.1093","volume":"10","author":[{"given":"Adekunle","family":"Alabi","sequence":"first","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mengyuan","family":"Ge","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jeremiah D","family":"Momper","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Shirley M","family":"Tsunoda","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael J","family":"Kelner","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Robert L","family":"Fitzgerald","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Raymond T","family":"Suhandynata","sequence":"additional","affiliation":[{"name":"Department of Pathology, UC San Diego Health , La Jolla, CA ,","place":["United States"]},{"name":"Skaggs School of Pharmacy and Pharmaceutical Sciences , UC San Diego Health, La Jolla, CA ,","place":["United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"286","published-online":{"date-parts":[[2025,1,31]]},"reference":[{"key":"2025050206372051800_jfae156-B1","doi-asserted-by":"crossref","first-page":"977","DOI":"10.1097\/00007890-199704150-00013","article-title":"A comparison of tacrolimus (FK506) and cyclosporine for immunosuppression after cadaveric renal transplantation","volume":"63","author":"Pirsch","year":"1997","journal-title":"Transplantation"},{"key":"2025050206372051800_jfae156-B2","doi-asserted-by":"crossref","first-page":"323","DOI":"10.2165\/00003495-200059020-00021","article-title":"Tacrolimus: a further update of its pharmacology and therapeutic use in the management of organ transplantation","volume":"59","author":"Plosker","year":"2000","journal-title":"Drugs"},{"key":"2025050206372051800_jfae156-B3","doi-asserted-by":"crossref","first-page":"1249","DOI":"10.7164\/antibiotics.40.1249","article-title":"FK-506, a novel immunosuppressant isolated from a Streptomyces. 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