Alternative Sampling Strategies in Therapeutic Drug Monitoring: Microsampling Growing Toward Maturity

Self-Sampling by Adolescents at Home: Assessment of the Feasibility to Successfully Collect Blood Microsamples by Inexperienced Individuals

Blood microsampling has increasingly attracted interest in the past decades as a more patient-centric sampling approach, offering the possibility to collect a minimal volume of blood following a finger or arm prick at home. In addition to conventional dried blood spots (DBS), many different devices allowing self-sampling of blood have become available. Obviously, the success of home-sampling can only be assured when (inexperienced) users collect samples of good quality. Therefore, the feasibility of six different microsampling devices to collect capillary blood by inexperienced adolescents at home was evaluated. Participants (n = 95) were randomly assigned to collect blood (dried or liquid) at different time points using four of six different self-sampling devices (i.e., DBS, Mitra volumetric absorptive microsampling (VAMS), Capitainer B, Tasso M20, Minicollect tube and Tasso+ serum separator tube (SST)). The quality of the samples was visually inspected and analytically determined. Moreover, the participants' satisfaction was assessed via questionnaires. Although a majority succeeded based on the visual inspection, the success rate differed largely between the different devices. In general, the lowest success rate was obtained for the Minicollect tubes, although there is an opportunity and need for improvement for the other self-sampling devices as well. Hence, this also emphasizes the importance to assess the quality of samples collected by the target population prior to study initiation. In addition, visual classification by a trained individual was confirmed based on assessment of the analytical variability between replicates. Finally, self-sampling at home was overall (very) positively received by the participants.

Dried blood spot sampling for therapeutic drug monitoring: challenges and opportunities

INTRODUCTION

The use of dried blood spots (DBS) has gained interest in the field of therapeutic drug monitoring (TDM) due to its potential advantages, such as minimally invasive capillary blood collection, potential stabilization of drugs and metabolites at room or high temperatures, and lower biohazard, allowing for inexpensive storage and transportation. However, there are several drawbacks to the clinical use of DBS in TDM, mostly related to hematocrit (Hct) effects, differences between venous and capillary blood concentrations, among others, that must be evaluated during analytical and clinical method validation.

AREA COVERED

This review focuses on the most recent publications on the applications of DBS sampling for TDM (2016-2022), with a special focus on the challenges presented by this alternative sampling strategy, as well as the opportunities for clinical applications. Real-life studies presenting clinical applications were reviewed.

EXPERT OPINION

With the availability of method development and validation guidelines for DBS-based methods in TDM, higher levels of assay validation standardization have been achieved, expanding the clinical applications of DBS sampling in patient care. New sampling devices that overcome the limitations of classical DBS, such as the Hct effects, will further encourage the use of DBS in routine TDM.

Method development for the quantification of lead levels in whole blood sampled on Mitra® with VAMS® tips by inductively coupled plasma-MS/MS

Background: Lead is harmful for humans by having adverse effects on different biological systems. Venepuncture is the gold standard for blood lead level analysis, but this method has many flaws. The goal of this research was to develop and validate a more practical approach for blood sampling. Materials & methods: Mitra^® devices based on VAMS^® and inductively coupled plasma-MS/MS technologies were employed. Performance evaluation of the newly developed method was also performed by comparing it versus a commonly used method at the Centre de Toxicologie du Québec for blood lead level analysis. Results: Comparison showed no signs of significant difference between the two methods. Conclusion: VAMS may be a useful alternative sampling approach for further research on blood lead analysis and possibly for many other trace elements.

Application of non-contact hematocrit prediction technologies to overcome hematocrit effects on immunosuppressant quantification from dried blood spots

Fully automated dried blood spot (DBS) analysis for therapeutic drug monitoring (TDM) of the immunosuppressants tacrolimus, sirolimus, everolimus and cyclosporin A suffers from a so-called hematocrit (hct) effect. This effect is related to the analysis of a partial DBS punch and extractability differences imposed by blood with different hcts. As this is intrinsic to automated DBS analysis, this poses a serious drawback for accurate immunosuppressant quantification. Knowledge of a sample's hct allows to correct the derived immunosuppressant concentrations for this effect. Unfortunately, when using the DBS approach for sampling at patients' homes, this hct will typically not be available. The aim of this study was to investigate the validity of a correction algorithm during fully automated DBS analysis of immunosuppressants, based on knowledge of the DBS' hct, obtained via two distinct non-contact hematocrit prediction strategies, using either near-infrared (NIR) or ultra-violet/visible (UV/VIS) spectroscopy. For tacrolimus, sirolimus, everolimus, and cyclosporin A, 48, 47, 58 and 48 paired venous whole blood and venous DBS patient samples were collected, respectively, and analyzed using an automated DBS-MS 500 HCT extraction unit coupled to a liquid chromatography tandem mass spectrometry system. Additionally, for all 201 samples the hct of the DBS was predicted based on NIR and UV/VIS spectroscopy. For tacrolimus and cyclosporin A, both hct prediction strategies allowed for adequate correction of the hct effect. Also for sirolimus and everolimus the results greatly improved after hct correction, although a hct bias remained for sirolimus and for everolimus a slightly significant hct effect was observed after NIR- and UV/VIS-based correction. Application of both hct prediction strategies ensured that clinical acceptance limits (i.e. ≥ 80% of the samples within 20% difference compared to whole blood) were met for all analytes. In conclusion, we demonstrated that non-contact hct prediction strategies, applied in tandem with fully automated DBS analysis, can be used to adequately correct immunosuppressant concentrations, yielding a good agreement with whole blood.

Reliability and feasibility of home-based dried blood spot in therapeutic drug monitoring: a systematic review and meta-analysis

PURPOSE

Dried blood spot (DBS) is one of promising home sampling methods for therapeutic drug monitoring (TDM). However, the associated reliability and feasibility (including yield, adherence, and preference), which are criteria for the promotion of home-based DBS, remain unknown. This systematic review and meta-analysis aimed to evaluate the reliability and feasibility of TDM using DBS sampling.

METHODS

In this study, a combination of MeSH and free terms for (dried blood spot*[title/abstract])AND ("Drug Monitoring"[Mesh])AND(home OR venous)was surveyed using EMBASE, PubMed, Cochrane Library, and Web of Science upon gathering published. we registered this study protocol with the International Prospective Registry of Systematic Reviews (CRD42021247559).

RESULTS

Approximately half (35/75) of the evaluations reported good agreement between DBS and plasma, and the results for drugs with poor agreement may be improved using a haematocrit-based physiological equation. The yield and adherence to home-based DBS exceeded 87%, and questionnaire-based preference for DBS was 77%.

CONCLUSIONS

DBS may be a reliable and feasible home sampling method; however, it requires intricate design and evaluation before implementation.

Application of machine learning to predict tacrolimus exposure in liver and kidney transplant patients given the MeltDose formulation

PURPOSE

Machine Learning (ML) algorithms represent an interesting alternative to maximum a posteriori Bayesian estimators (MAP-BE) for tacrolimus AUC estimation, but it is not known if training an ML model using a lower number of full pharmacokinetic (PK) profiles (= "true" reference AUC) provides better performances than using a larger dataset of less accurate AUC estimates. The objectives of this study were: to develop and benchmark ML algorithms trained using full PK profiles to estimate MeltDose^®-tacrolimus individual AUCs using 2 or 3 blood concentrations; and to compare their performance to MAP-BE.

METHODS

Data from liver (n = 113) and kidney (n = 97) transplant recipients involved in MeltDose-tacrolimus PK studies were used for the training and evaluation of ML algorithms. "True" AUC0-24 h was calculated for each patient using the trapezoidal rule on the full PK profile. ML algorithms were trained to estimate tacrolimus true AUC using 2 or 3 blood concentrations. Performances were evaluated in 2 external sets of 16 (renal) and 48 (liver) transplant patients.

RESULTS

Best estimation performances were obtained with the MARS algorithm and the following limited sampling strategies (LSS): predose (0), 8, and 12 h post-dose (rMPE = - 1.28%, rRMSE = 7.57%), or 0 and 12 h (rMPE = - 1.9%, rRMSE = 10.06%). In the external dataset, the performances of the final ML algorithms based on two samples in kidney (rMPE = - 3.1%, rRMSE = 11.1%) or liver transplant recipients (rMPE = - 3.4%, rRMSE = 9.86%) were as good as or better than those of MAP-BEs based on three time points.

CONCLUSION

The MARS ML models developed using "true" MeltDose^®-tacrolimus AUCs yielded accurate individual estimations using only two blood concentrations.

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.

Evaluation of hemaPEN® sampling device for measurement of cocaine and metabolites in capillary blood by LC-MS/MS

Background: Dried blood spot sampling has been reported for on-site collection of specimens, but measurements are affected by blood hematocrit, and special handling is required, especially for forensic applications. The hemaPEN^® blood collection device was developed to produce spots with constant volume. Results: Linearity between 1 and 500 ng/ml was shown for cocaine and the metabolites benzoylecgonine and cocaethylene. The assay demonstrated acceptable precision and accuracy, and analytes were stable for 7 days when kept inside hemaPEN devices. Accuracy of the assay was affected by hematocrit but was within acceptable limits. Conclusion: Use of the hemaPEN, which retains dried blood within the device, could be advantageous for the quantification of illicit drugs in capillary blood compared with conventional dried blood spot collection.

Development and Validation of a Dried Blood Spot Assay Using UHPLC-MS/MS to Identify and Quantify 12 Antihypertensive Drugs and 4 Active Metabolites: Clinical Needs and Analytical Limitations

PURPOSE

As nonadherence to antihypertensive drugs (AHDs) can increase the risk of cardiovascular events, hospitalization, and higher costs, there is a need for a reliable, objective, and easy method to assess nonadherence in patients. The dried blood spot (DBS) sampling method used to measure drug concentrations meets these requirements. For detecting nonadherence, identification is more important than quantification. Owing to their use in clinical practice, it is important to measure multiple AHDs with a single method. Therefore, we developed and validated a single DBS method for 17 commonly used AHDs and 4 active metabolites using ultrahigh performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS).

METHODS

Analytical validation of the DBS assay was performed in accordance with the guidelines on bioanalytical method validation of the European Medicines Agency and US Food and Drug Administration as well as the International Association of Therapeutic Drug Monitoring and Clinical Toxicology guidelines.

RESULTS

We validated 12 of the 17 AHDs according to the European Medicines Agency and Food and Drug Administration requirements for bioanalytical method validation. Eleven AHDs were validated for both identification and quantification of drug concentrations, whereas nifedipine was only validated for identification. However, 5 of the 17 AHDs were excluded due to suboptimal validation results. Lercanidipine was excluded due to nonlinearity, and all 4 AHDs measured in the negative mode of UHPLC-MS/MS were not in accordance with one or more of the acceptance criteria and were therefore excluded.

CONCLUSIONS

The described method accurately measured AHDs in DBS and can be used to determine nonadherence in patients. However, method validation revealed a challenging balance between analytical limitations and clinical needs when analyzing multiple drugs using the same method.

The Effect of the Physical Morphology of Dried Biofluids on the Chemical Stability of Analytes Stored in Paper and Direct Analysis by Mass Spectrometry

Three-dimensional (3D) dried blood spheroids formed on hydrophobic paper are a new microsampling platform that can stabilize labile molecules in whole blood stored in ambient air at room temperature. In this study, we define the ideal conditions for preparing the dried blood spheroids. The physical morphology of 3D dried blood spheroids is found to be largely impacted by the unregulated relative humidity of the surrounding environment. A solution of KOH placed in an enclosed chamber offers a facile way to control humidity. We also report a general polymer coating strategy that serves to stabilize dried biofluids when prepared under ordinary ambient conditions without regulation of humidity. Dried blood spheroids coated in xanthan gum polymer exhibited enhanced chemical and physical stability. The same xanthan gum polymer provided chemical stability for 2D dried blood spots when compared with the conventional noncoated samples. We have expanded the application of xanthan gum to less viscous biofluids such as urine to induce an artificial protective barrier that also provides enhanced stability for labile performance-enhancing drugs stored at room temperature. The impact of polymer coating on direct biofluid analysis via paper spray mass spectrometry was determined by comparing the relative ionization efficiency, percent difference of ionization efficiency, and matrix effects of performance-enhancing drugs that were spiked in undiluted raw urine. Acceptable analytical performance was recorded for all three criteria, including high ionization efficiencies that ranged from 77 to 93% in the presence of the xanthan gum polymer.

Living in a transient world: ICP-MS reinvented via time-resolved analysis for monitoring single events

After 40 years of development, inductively coupled plasma-mass spectrometry (ICP-MS) can hardly be considered as a novel technique anymore. ICP-MS has become the reference when it comes to multi-element bulk analysis at (ultra)trace levels, as well as to isotope ratio determination for metal(loid)s. However, over the last decade, this technique has managed to uncover an entirely new application field, providing information in a variety of contexts related to the individual analysis of single entities (e.g., nanoparticles, cells, or micro/nanoplastics), thus addressing new societal challenges. And this profound expansion of its application range becomes even more remarkable when considering that it has been made possible in an a priori simple way: by providing faster data acquisition and developing the corresponding theoretical substrate to relate the time-resolved signals thus obtained with the elemental composition of the target entities. This review presents the underlying concepts behind single event-ICP-MS, which are needed to fully understand its potential, highlighting key areas of application (e.g., single particle-ICP-MS or single cell-ICP-MS) as well as of future development (e.g., micro/nanoplastics).

In-depth evaluation of automated non-contact reflectance-based hematocrit prediction of dried blood spots

Using the automated CAMAG® DBS-MS 500 HCT system, a UV-Vis-based hematocrit prediction calibration model was succesfully set up and applied on both an independent instrument and an independent set of venous DBS samples.