Fingerprick Microsampling Methods Can Replace Venepuncture for Simultaneous Therapeutic Drug Monitoring of Tacrolimus, Mycophenolic Acid, and Prednisolone Concentrations in Adult Kidney Transplant Patients

Development and Clinical Validation of a Volumetric Absorptive Capillary Microsampling Method for Quantification of Mycophenolic Acid and Mycophenolic Acid Glucuronide in Kidney Transplant Recipients

BACKGROUND

Mycophenolic acid (MPA) is a cornerstone of immunosuppressive treatment in kidney transplant recipients (KTRs). Traditional therapeutic drug monitoring for MPA is based on venous blood sampling. Finger-prick capillary microsampling is patient-friendly and enables limited sampling to predict the area under the curve. A liquid chromatography-tandem mass spectrometry assay was used to detect MPA and its metabolite mycophenolic acid glucuronide (MPAG) using volumetric absorptive capillary microsampling (VAMS) was developed and clinically validated.

METHODS

An assay based on VAMS and liquid chromatography-tandem mass spectrometry was validated bioanalytically and clinically. Agreement between dried microsamples and plasma samples was investigated in KTR on mycophenolate mofetil therapy. Paired microsamples and plasma samples were obtained before and at 0.5 and 2 hours postdosing. The samples were divided into development (75%) and validation (25%) datasets. Conversion from VAMS to plasma concentrations was established using a regression model, with at least 67% of paired samples required to fall within a mean relative difference of ±20%.

RESULTS

Twelve KTRs (median age: 49 years) provided 69 paired microsamples and plasma samples. For the VAMS method, the between-series mean accuracy was 90%-106% with a coefficient of variation <7% at concentrations of 0.25-32 mg/L (MPA) and 2.5-320 mg/L (MPAG). A conversion equation based on the regression model was applied and validated using an independent dataset. The mean relative differences between corrected microsamples and plasma samples were 1.9% for MPA and 2.7% for MPAG, with <5% outside ±20% for both analytes. Dried microsamples were stable for 3 months at ambient temperature.

CONCLUSIONS

The VAMS method demonstrated acceptable performance. MPA and MPAG can be reliably quantified using VAMS and are suitable for patient self-sampling in clinical pharmacokinetics studies of KTR.

Microsampling techniques and patient-centric therapeutic drug monitoring of immunosuppressants

Immunosuppressive pharmacotherapy after solid organ transplantation (SOT) requires therapeutic drug monitoring (TDM) for therapy individualization. The venous whole blood is still considered as routine matrix for monitoring immunosuppressive drug concentration. On the other hand, as an alternative, capillary blood collected using noninvasive sampling is convergent with a patient-centric approach. Despite their disadvantages regarding sample homogeneity and the hematocrit effect, well-known dried blood spot techniques have shown promising results. Volumetric absorptive microsampling (VAMS) and quantitative dried blood spot (qDBS) have successfully eliminated these unfavorable biased elements. Microsampling can be used in transplant recipients' care, mainly due to long-term therapy under control drug concentrations and the long distance between the place of the patient's residence and the diagnostic laboratory in the transplant center. The study aimed to discuss the clinical consequences of implementing microsampling techniques for TDM of immunosuppressants. Additionally, we have discussed the 'hot topics' in microsampling: home-based self-sampling, adherence to therapy monitoring, and drug concentration conversion to estimated traditional matrices. Finally, based on our experience and current practice, we propose best practices for microsampling implementation from bench to bedside. Microsampling techniques can potentially revolutionise immunosuppressive pharmacotherapy by enabling patient-centric individualisation in various subpopulations, significantly improving post-transplant care.

Implementation of Volumetric Finger-Prick Self-Sampling for Therapeutic Drug Monitoring of Immunosuppressants After Kidney Transplantation: Lessons Learned From the Practice

BACKGROUND

Home-based hospital services are becoming increasingly popular, and the addition of remote outpatient appointments after kidney transplantation facilitates more practical and closer follow-up. In this context, finger-prick self-sampling is an important aspect of monitoring of immunosuppressants and biomarkers. Nevertheless, several issues must be addressed to ensure the feasibility and quality when implementing microsampling in clinical practice. We summarize our experiences and opinions in this field.

METHODS

This article is based on the authors' experience regarding the laboratory and clinical implementation of finger-prick self-sampling in kidney transplant recipients. The referenced literature is related to the authors' knowledge in this field.

RESULTS

We present considerations for the selection of relevant analytes, key characteristics of selected volumetric sampling tools (Mitra and Capitainer), and the associated sampling pitfalls. In addition, we address the requirements for patients performing finger-prick sampling, appropriate design of methods and workflow, critical points for validation, and aspects related to logistics and digital solutions.

CONCLUSIONS

Volumetric finger-prick self-sampling is suitable for monitoring immunosuppressants and certain biomarkers that are relevant to outpatient follow-up after kidney transplantation. We believe that a carefully designed system for the entire workflow, including patient training, will be beneficial in enabling a safe experience for transplant recipients, as well as ensuring overall efficiency and adequate quality. In the future, a combination of immunosuppressants with a wide range of biomarkers has significant potential for use in at-home self-sampling after kidney transplantation.

Clinical validation of two volumetric absorptive microsampling devices to support home-based therapeutic drug monitoring of immunosuppression

AIMS

Dried blood volumetric absorptive microsamples (VAMS) may facilitate home-based sampling to enhance therapeutic drug monitoring after transplantation. This study aimed to clinically validate a liquid chromatography-tandem mass spectrometry assay using 2 VAMS devices with different sampling locations (Tasso-M20 for the upper arm and Mitra for the finger). Patient preferences were also evaluated.

METHODS

Clinical validation was performed for tacrolimus and mycophenolic acid by comparison of paired VAMS and venipuncture samples using Passing-Bablok regression and Bland-Altman analysis. Conversion of mycophenolic acid VAMS to serum concentrations was evaluated using haematocrit-dependent formulas and fixed correction factors defined a priori. Patients' perspectives, including useability, acceptability and feasibility, were also investigated using established questionnaires.

RESULTS

Paired samples (n = 50) were collected from 25 kidney transplant recipients. Differences for tacrolimus whole-blood concentration were within ±20% for 86 and 88% of samples from the upper arm and fingerstick, respectively. Using correction factors of 1.3 for the upper-arm and 1.47 for finger-prick samples, 84 and 76% of the paired samples, respectively, were within ±20% for mycophenolic acid serum concentration. Patient experience surveys demonstrated limited pain and acceptable useability of the upper-arm device.

CONCLUSIONS

Tacrolimus and mycophenolic acid can be measured using 2 common VAMS devices with similar analytical performance. Patients are supportive of home-based monitoring with a preference for the Tasso-M20 device.

Use of volumetric absorptive microsampling and parallel reaction monitoring mass spectrometry for tacrolimus blood trough measurements at home in pediatric heart transplant patients

Background

Measurement of trough levels for calcineurin inhibitors by venipuncture sampling is a mainstay of patient management in solid organ transplant recipients but challenging in pediatric patients. Volumetric Absorptive Microsampling (VAMS) is a patient-friendly, minimally invasive sampling technique to accurately collect blood. An assay for measurement of tacrolimus in blood using VAMS, coupled with parallel reaction monitoring (PRM) mass spectrometry, was validated in pediatric heart transplant patients.

Methods

Tacrolimus was measured by a newly developed high-resolution PRM assay and compared with low-resolution tandem mass spectrometry (MRM). Dried blood samples were collected from pediatric heart transplant patients (n = 35) using VAMS devices and a satisfaction survey was completed by patients/guardians. Tacrolimus concentrations were compared across whole liquid blood, dried blood spots, and capillary blood, and shipping stability determined.

Results

The PRM assay was linear over a range 1-50 ng/mL, similar to MRM but had greater specificity due to reduced background noise. No significant differences in tacrolimus concentrations were observed between VAMS and venous blood. Tacrolimus dried on VAM tips was stable for 14 days and concentrations were unaffected by postal shipping. The variability in two simultaneously collected at-home patient samples was minimal - average concentration difference was 0.12 ± 0.94 ng/mL (p = 0.6) between paired samples.

Conclusion

A high resolution PRM mass spectrometry assay was developed for home-based dried blood collections for therapeutic monitoring of tacrolimus. The advantage of PRM was enhanced specificity and the VAMS devices provided a simple and convenient approach to blood sampling at home in pediatric heart transplant patients.

Decentralized clinical trial design using blood microsampling technology for serum bioanalysis

Background: Alternatives to phlebotomy in clinical trials increase options for patients and clinicians by simplifying and increasing accessibility to clinical trials. The authors investigated the technical and logistical considerations of one technology compared with phlebotomy. Methodology: Paired samples were collected from 16 donors via a second-generation serum gel microsampling device and conventional phlebotomy. Microsamples were subject to alternative sample handling conditions and were evaluated for quality, clinical testing and proteome profiling. Results: Timely centrifugation of blood serum microsamples largely preserved analyte stability. Conclusion: Centrifugation timing of serum microsamples impacts the quality of specific clinical chemistry and protein biomarkers. Microsampling devices with remote centrifugation and refrigerated shipping can decrease patient burden, expand clinical trial populations and aid clinical decisions.

Therapeutic drug monitoring of mycophenolic acid (MPA) using volumetric absorptive microsampling (VAMS) in pediatric renal transplant recipients: ultra-high-performance liquid chromatography-tandem mass spectrometry analytical method development, cross-validation, and clinical application

BACKGROUND

Mycophenolic acid (MPA) is widely used in posttransplant pharmacotherapy for pediatric patients after renal transplantation. Volumetric absorptive microsampling (VAMS) is a recent approach for sample collection, particularly during therapeutic drug monitoring (TDM). The recommended matrix for MPA determination is plasma (PL), and conversion between capillary-blood VAMS samples and PL concentrations is required for the appropriate interpretation of the results.

METHODS

This study aimed to validate and develop a UHPLC-MS/MS method for MPA quantification in whole blood (WB), PL, and VAMS samples, with cross and clinical validation based on regression calculations. Methods were validated in the 0.10-15 µg/mL range for trough MPA concentration measurement according to the European Medicines Agency (EMA) guidelines. Fifty pediatric patients treated with MPA after renal transplantation were included in this study. PL and WB samples were obtained via venipuncture, whereas VAMS samples were collected after the fingerstick. The conversion from VAMS_MPA to PL_MPA concentration was performed using formulas based on hematocrit values and a regression model.

RESULTS

LC-MS/MS methods were successfully developed and validated according to EMA guidelines. The cross-correlation between the methods was evaluated using Passing-Bablok regression, Bland-Altman bias plots, and predictive performance calculations. Clinical validation of the developed method was successfully performed, and the formula based on regression was successfully validated for VAMS_MPA to PL_MPA concentration and confirmed on an independent group of samples.

CONCLUSIONS

This study is the first development of a triple matrix-based LC-MS/MS method for MPA determination in the pediatric population after renal transplantation. For the first time, the developed methods were cross-validated with routinely used HPLC-DAD protocol.

Dried blood microsampling-assisted therapeutic drug monitoring of immunosuppressants: An overview

In the field of solid organ transplantation, chemotherapy and autoimmune disorders, treatment with immunosuppressant drugs requires intensive follow-up of the blood concentrations via therapeutic drug monitoring (TDM) because of their narrow therapeutic window and high intra- and inter-subject variability. This requires frequent hospital visits and venepunctures to allow the determination of these analytes, putting a high burden on the patients. In the context of patient-centric thinking, it is becoming increasingly established that at least part of these conventional blood draws could be replaced by microsampling, allowing home-sampling and increasing the quality of life for these patients. In this review we discuss the published methods - mostly using liquid chromatography coupled to tandem mass spectrometry - that have utilized (volumetric) dried blood samples as an alternative for conventional liquid whole blood for the TDM of immunosuppressant drugs. Furthermore, some pre-analytical considerations using DBS or volumetric alternatives are considered, as well as the applicability on clinical samples. The implementation status in clinical practice is also discussed, including (1) the cost-effectiveness of this approach compared to venepuncture, (2) the availability of multiplexed methods, (3) the status of harmonization and (4) patient perception. A brief perspective on potential future developments for the dried blood-based TDM of immunosuppressant drugs is provided, by considering how obstacles for the implementation of these strategies into clinical practice might be overcome.

Volumetric Absorptive Microsampling in Therapeutic Drug Monitoring of Immunosuppressive Drugs-From Sampling and Analytical Issues to Clinical Application

Miniaturisation and simplification are novel approaches in clinical bioanalysis, especially in therapeutic drug monitoring (TDM). These contemporary trends are related to the sampling, pre-treatment, and analysis of biological fluids. Currently, dried blood spot (DBS), one of the most popular microsampling techniques, is feasible and inexpensive. However, obtaining reliable results with sample homogeneity and volume variability is difficult. Volumetric Absorptive Microsampling (VAMS) has recently enabled the accurate and precise collection of a fixed blood volume. It reduced the hematocrit effect, improved volumetric accuracy, and generated results correlating with the dose and drug exposure from wet blood. This review focuses on VAMS-Mitra™ devices, which have become increasingly important since 2014, mainly for TDM and toxicology studies. First, the current literature has been reviewed based on immunosuppressants and their determination in samples obtained using Mitra™. Second, the critical points, weaknesses, and strengths have been characterized in contrast to classic venipuncture and other microsampling methods. Finally, we indicate the points of attention according to the perspective of Mitra™ as well as its usefulness in clinical practice. VAMS is currently state-of-the-art in microsampling and seems to be a good instrument for improving adherence to immunosuppressive therapy, especially in the pediatric population.