MSACL 2024 Abstract

Tacrolimus Concentrations in Envarsus vs Prograf Patients: An Evaluation of the Clinical Impact of LC-MS/MS and Immunoassay Methods on Tacrolimus Measurement

Adekunle Alabi (1), Mengyuan Ge (1), Robert Fitzgerald (1), Raymond T. Suhandynata (1,2)
(1) Department of Pathology, UC San Diego Health, La Jolla (2) Skaggs School of Pharmacy and Pharmaceutical Sciences, La Jolla

Adekunle Alabi, PhD (Presenter) University of Colorado Anschutz Medical Campus

Presenter Bio: I am a dedicated researcher with a profound interest in clinical chemistry and toxicology. The cornerstone of my work is the application of mass spectrometry techniques in toxicological analysis and therapeutic drug monitoring. These powerful tools allow me to achieve precise and accurate measurements of chemical substances in biological samples, ensuring that patient care is both safe and effective.

Driven by a commitment to improve patient care and outcomes, I focus on precise monitoring and the development of innovative therapeutic approaches. By leveraging the capabilities of mass spectrometry, I strive to push the boundaries of what is known in these fields, contributing valuable insights and advancements.

Relevant Financial Disclosures (within past 24 months, reported on Feb 12, 2025) No relevant financial relationship(s) to disclose. Conflict mitigation NOT REQUIRED.

INTRODUCTION: Tacrolimus is a calcineurin inhibitor used as part of an immunosuppressive regimen in kidney and liver transplant patients to prevent graft-versus-host disease (GvHD) and requires therapeutic drug monitoring due to its narrow therapeutic index. Tacrolimus levels are commonly measured using two different methodologies – Immunoassay and liquid chromatography tandem mass spectrometry (LC-MS/MS). A global proficiency study to assess and compare the measurement of trough levels by these two methodologies noted a positive bias with the ARCHITECT immunoassay which is likely due to the presence of tacrolimus metabolites.

OBJECTIVES: The aim of our study is to assess the impact of two different formulations of tacrolimus on the accuracy of its analytical measurement. While differences between immunoassay and LC-MS/MS results have been evaluated for immediate-release tacrolimus (Prograf), it has yet to be characterized for extended-release formulations such as Envarsus. The discrepancy between immunoassay and LC-MS/MS has clinical implications, as dosage modifications are based on measured concentrations, analytical variation may cause intervals of subtherapeutic or supratherapeutic exposure, increasing the risk of graft rejection or toxicity.

METHODS: Development of an LC-MS/MS method for the simultaneous quantification of tacrolimus and its major metabolite, desmethyl tacrolimus, was performed in whole blood using traceable calibrators and quality control material for tacrolimus and standard material for desmethyl tacrolimus. Tacrolimus concentrations were measured by LC-MS/MS and ARCHITECT immunoassay methods in excess whole blood specimens from patients treated with either Prograf or Envarsus undergoing standard clinical monitoring at UCSD Health. Measurement biases between LC-MS/MS and immunoassay methodologies were determined for both formulations of tacrolimus.

RESULTS: External calibration curves for both tacrolimus and desmethyl tacrolimus were linear (R2>0.995), and the analytical measurement range (AMR) for tacrolimus spanned from 1.1 - 31.6 ng/ml. Calibrator and Quality control (QC) biases were within 15% of their target values throughout the AMR and within-run imprecision was less than 10% (n=25) for all calibrators and QCs. Between-run imprecision for Low, Mid, and High QC levels over a period of 2 weeks (n=5 days) was less than 10%. Comparative bias of tacrolimus concentrations between immunoassay and LC-MS/MS was significantly lower (P value=0.0342) for Envarsus (n=11 specimens) relative to Prograf (n=17 specimens).

CONCLUSION: The differential bias between immunoassay and LC-MS/MS in the measurement of tacrolimus in patients dosed with immediate-release versus extended-release formulations suggests that their distinct pharmacokinetic profile may impact the accuracy of the measurement. Therefore, applying observed measurement biases from different assays derived from Prograf patients to Envarsus patients and vice versa may result in erroneous estimation of tacrolimus concentrations.