Advancing Therapeutic Drug Monitoring for Oral Targeted Anticancer Drugs: From Hospital-Based Towards Home-Sampling

Home-sampling for therapeutic drug monitoring (TDM) for oral targeted anticancer drugs offers a promising alternative to traditional hospital-based sampling methods, though it presents challenges. This review aims to summarize the state-of-the-art of home-sampling methods for TDM and evaluates the analytical and clinical validation challenges. A comprehensive search was conducted across Embase, Medline, and Scopus. Eligible articles described analytical and/or clinical validation of home-sampling methods for oral targeted anticancer drugs. ASReview was used to process unique references and to identify relevant studies. Of the 39 included articles, 32 detailed on analytical validation experiments, while 27 covered clinical validation experiments. Dried blood spot and volumetric absorptive microsampling were the primary sampling methods. Key challenges were ensuring robust sample collection, sample pretreatment, hematocrit effects, and sample stability, which were generally thoroughly investigated. Clinical validation yielded promising results for most analytes, although external validation remains crucial for confirming reliability. Home-sampling methods for TDM of oral targeted anticancer drugs show promising results for clinical implementation. Methods for well-studied drugs may be clinically implemented immediately, while others require further external validation. Future research should address device-specific challenges and assess patient feasibility to facilitate the routine use of home-sampling in clinical practice.

Surface-Enhanced Raman Spectroscopy Combined with Multivariate Analysis for Fingerprinting Clinically Similar Fibromyalgia and Long COVID Syndromes

Fibromyalgia (FM) is a chronic central sensitivity syndrome characterized by augmented pain processing at diffuse body sites and presents as a multimorbid clinical condition. Long COVID (LC) is a heterogenous clinical syndrome that affects 10-20% of individuals following COVID-19 infection. FM and LC share similarities with regard to the pain and other clinical symptoms experienced, thereby posing a challenge for accurate diagnosis. This research explores the feasibility of using surface-enhanced Raman spectroscopy (SERS) combined with soft independent modelling of class analogies (SIMCAs) to develop classification models differentiating LC and FM. Venous blood samples were collected using two supports, dried bloodspot cards (DBS, n = 48 FM and n = 46 LC) and volumetric absorptive micro-sampling tips (VAMS, n = 39 FM and n = 39 LC). A semi-permeable membrane (10 kDa) was used to extract low molecular fraction (LMF) from the blood samples, and Raman spectra were acquired using SERS with gold nanoparticles (AuNPs). Soft independent modelling of class analogy (SIMCA) models developed with spectral data of blood samples collected in VAMS tips showed superior performance with a validation performance of 100% accuracy, sensitivity, and specificity, achieving an excellent classification accuracy of 0.86 area under the curve (AUC). Amide groups, aromatic and acidic amino acids were responsible for the discrimination patterns among FM and LC syndromes, emphasizing the findings from our previous studies. Overall, our results demonstrate the ability of AuNP SERS to identify unique metabolites that can be potentially used as spectral biomarkers to differentiate FM and LC.

Validation of low-volume sampling devices for pharmacokinetic analysis: technical and logistical challenges and solutions

While low-volume sampling technologies offer numerous advantages over venipuncture, implementation in clinical trials poses technical and logistical challenges. Bioanalytical methods were validated for measuring the concentration of crenezumab and etrolizumab in dried blood samples collected using Mitra and Tasso-M20. The data generated demonstrate that the concentrations of crenezumab and etrolizumab in dried blood collected by either device could be determined using calibrators prepared in serum. Drug concentrations from dried blood were converted to serum concentrations using patient hematocrit levels. Contract Research Organization experience in sample handling and analysis allowed us to compare differences between various low-volume sampling technologies. This study evaluated challenges and presented potential solutions for use of different low-volume sampling technologies for pharmacokinetic analysis.

Clinical Bridging Studies and Modeling Approach for Implementation of a Patient Centric Sampling Technique in Padsevonil Clinical Development

Volumetric absorptive microsampling (VAMS) techniques have gained popularity these last years as innovative tool for collection of blood pharmacokinetic (PK) samples in clinical trials as they offer many advantages over dried blood spot and conventional venous blood sampling. The use of Mitra®, a blood collection device based on volumetric absorptive microsampling (VAMS) technology, was implemented during clinical development of padsevonil (PSL), an anti-seizure medication (ASM) candidate. The present study describes the approach used to bridge plasma (obtained from conventional venous blood sampling) and blood exposures (obtained with Mitra®) to support the use of Mitra as sole blood PK sampling method in clinical trials. Paired blood (using Mitra®) and plasma samples (using conventional venous blood sampling) were collected in healthy volunteers as well as in patients with epilepsy. PSL concentration in plasma and blood were analyzed using different approaches which included evaluation of blood-to-plasma ratios (B/P) over time, linear regression, Bland-Altman analysis as well as development of a linear-mixed effect model based on clinical pharmacology studies. Results showed that the observed in vivo B/P and the measured bias between the 2 collection methods were consistent with the measured in vitro B/P. Graphical analysis demonstrated a clear time effect on the B/P which was confirmed in the linear mixed effect model with sampling time identified as significant covariate. Finally, the built-in model was validated using independent datasets and was shown to adequately predict plasma concentration based on blood concentration with a mean bias of less than 9% (predicted versus observed plasma concentration).

Matrix-matched calibrators are necessary for robust and high-quality dried blood spots lead screening assays by inductively coupled plasma-mass spectrometry

Background and aims

Reliable lead screening methods are necessary to support early identification of lead exposure in children. Sample collection using dried blood spots (DBS) offers advantages compared to traditional venipuncture and capillary collection. Here, we describe and compare three lead DBS inductively coupled plasma-mass spectrometry (ICP-MS) methods for lead screening.

Materials and methods

Lead was extracted from Whatman 903 protein saver cards punches and analyzed by ICP-MS across three independent clinical laboratories. Each laboratory evaluated the performance of aqueous and matrix-matched DBS calibrators using external quality control samples (WI State of Laboratory of Hygiene Program). Leftover patient samples (n = 39) were used for an interlaboratory comparison of lead DBS. Lead DBS results were compared to whole blood methods.

Results

The DBS ICP-MS methods using matrix-matched DBS calibrators had superior performance to the aqueous calibrations. There was a strong correlation between lead measured in DBS (matrix-matched) and whole blood for the three methods evaluated.

Conclusion

Lead can be measured accurately by ICP-MS in DBS samples when matrix-matched calibrators are used. External quality control programs are valuable to assess the performance of DBS methods. DBS lead ICP-MS methods are a robust analytical option for lead screening even though the limitations of DBS are well recognized.

Volumetric Absorptive Microsampling in the Analysis of Endogenous Metabolites

Volumetric absorptive microsampling (VAMS) has arisen as a relevant tool in biological analysis, offering simplified sampling procedures and enhanced stability. Most of the attention VAMS has received in the past decade has been from pharmaceutical research, with most of the published work employing VAMS targeting drugs or other exogenous compounds, such as toxins and pollutants. However, biomarker analysis by employing blood microsampling has high promise. Herein, a comprehensive review on the applicability of VAMS devices for the analysis of endogenous metabolites/biomarkers was performed. The study presents a full overview of the analysis process, incorporating all the steps in sample treatment and validation parameters. Overall, VAMS devices have proven to be reliable tools for the analysis of endogenous analytes with biological importance, often offering improved analyte stability in comparison with blood under ambient conditions as well as a convenient and straightforward sample acquisition model.

Pharmacological aspects of antiseizure medications: From basic mechanisms to clinical considerations of drug interactions and use of therapeutic drug monitoring

Antiseizure medications (ASMs) are the cornerstone of treatment for patients with epilepsy. Several new ASMs have recently been introduced to the market, making it possible to better tailor the treatment of epilepsy, as well as other indications (psychiatry and pain disorders). For this group of drugs there are numerous pharmacological challenges, and updated knowledge on their pharmacodynamic and pharmacokinetic properties is, therefore, crucial for an optimal treatment outcome. This review focuses on educational approaches to the following learning outcomes as described by the International League Against Epilepsy (ILAE): To demonstrate knowledge of pharmacokinetics and pharmacodynamics, drug interactions with ASMs and with concomitant medications, and appropriate monitoring of ASM serum levels (therapeutic drug monitoring, TDM). Basic principles in pharmacology, pharmacokinetic variability, and clinically relevant approaches to manage drug interactions are discussed. Furthermore, recent improvements in analytical technology and sampling are described. Future directions point to the combined implementation of TDM with genetic panels for proper diagnosis, pharmacogenetic tests where relevant, and the use of biochemical markers that will all contribute to personalized treatment. These approaches are clinically relevant for an optimal treatment outcome with ASMs in various patient groups.

Applications of Volumetric Absorptive Microsampling Technique: A Systematic Critical Review

METHODS

A novel microsampling device called Volumetric Absorptive microsampling (VAMS), developed in 2014, appears to have resolved the sample inhomogeneity inherent to dried blood spots, with improved precision in the volume of sample collected for measuring drug concentration. A literature search was conducted to identify several analytical and pharmacokinetic studies that have used VAMS in recent years.

RESULTS

The key factors for proper experimental design and optimization of the extraction of drugs and metabolites of interest from the device were summarized. This review focuses on VAMS and elaborates on bioanalytical factors, method validation steps, and scope of this technique in clinical practice.

CONCLUSIONS

The promising microsampling method VAMS is especially suited for conducting pharmacokinetic studies with very small volumes of blood, especially in special patient populations. Clinical validation of every VAMS assay must be conducted prior to the routine practical implementation of this method.

Volumetric Absorptive Microsampling to Enhance the Therapeutic Drug Monitoring of Tacrolimus and Mycophenolic Acid: A Systematic Review and Critical Assessment

BACKGROUND

Volumetric absorptive microsampling (VAMS) is an emerging technique that may support multisample collection to enhance therapeutic drug monitoring in solid organ transplantation. This review aimed to assess whether tacrolimus and mycophenolic acid can be reliably assayed using VAMS and to identify knowledge gaps by providing granularity to existing analytical methods and clinical applications.

METHODS

A systematic literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The PubMed, Embase, and Scopus databases were accessed for records from January 2014 to April 2022 to identify scientific reports on the clinical validation of VAMS for monitoring tacrolimus and mycophenolic acid concentrations. Data on the study population, sample sources, analytical methods, and comparison results were compiled.

RESULTS

Data from 12 studies were collected, including 9 studies pertaining to tacrolimus and 3 studies on the concurrent analysis of tacrolimus and mycophenolic acid. An additional 14 studies that provided information relevant to the secondary objectives (analytical validation and clinical application) were also included. The results of the clinical validation studies generally met the method agreement requirements described by regulatory agencies, but in many cases, it was essential to apply correction factors.

CONCLUSIONSS

Current evidence suggests that the existing analytical methods that use VAMS require additional optimization steps for the analysis of tacrolimus and mycophenolic acid. The recommendations put forth in this review can help guide future studies in achieving the goal of improving the care of transplant recipients by simplifying multisample collection for the dose optimization of these drugs.

A whole blood microsampling furosemide assay: development, validation and use in a pediatric pharmacokinetic study

Background: Furosemide is a commonly used diuretic for the treatment of edema. The pharmacokinetics of furosemide in neonates as they mature remains poorly understood. Microsampling assays facilitate research in pediatric populations. Results: We developed and validated a liquid chromatography-tandem mass spectrometry method for the quantitation of furosemide in human whole blood with volumetric absorptive microsampling (VAMS) devices (10 μl). Furosemide was stable in human whole blood VAMS under the study's assay conditions. This work established stability for furosemide for 161 days when stored as dried microsamples at -78°C. Conclusion: This method is being applied for the quantitation of furosemide in whole blood VAMS in an ongoing prospective pediatric clinical study. Representative clinical data are reported.

UHPLC-HRMS Method for the Simultaneous Screening of 235 Drugs in Capillary Blood for Doping Control Purpose: Comparative Evaluation of Volumetric and Non-volumetric Dried Blood Spotting Devices

We present a quick and simple multi-targeted analytical workflow based on ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry for the screening in dried blood spots and dried plasma spots of a wide variety of drugs with different chemical properties. Seven different microsampling devices were evaluated in view of their application for the detection of the selected target analytes in the framework of doping control analysis. The extraction of the analytes was optimized by assessing the efficacy of protocols based on ultrasonication with aqueous buffers and/or organic solvents of different polarities. Optimal recoveries were obtained by using pure methanol or mixtures of methanol/acetonitrile and methanol/isopropanol, depending on both the device and the target analytes. The method was fully validated according to both ISO17025 and the requirements of the World Anti-Doping Agency: all the analytes were clearly distinguishable from the matrix, with limits of detection in the range of 0.1-3.0 ng mL-1. Stability studies simulating the storage of samples before the analysis and in view of a possible re-analysis showed that most of the analytes were stable for at least 24 h at 50 °C and for at least 3 weeks at 25 and at 4 °C. The real applicability of the method was assessed by analyzing the samples collected after the administration of two model drugs, acetazolamide and deflazacort. The performance of the method was confirmed to be fit for purpose, and data obtained in blood can also be used to complement those available in urine, allowing to refine the knowledge concerning the pharmacokinetic profiles.

Application of a new volumetric microsampling device for quantitative bioanalysis of immunosuppression

Background: Volumetric absorptive microsampling may reduce the blood collection burden associated with therapeutic drug monitoring of immunosuppression to prevent organ transplant rejection. This work describes the development of a laboratory and analytical technique for quantifying tacrolimus and mycophenolic acid (MPA) from the Tasso-M20™ in human whole blood using bead-based impact-assisted extraction. Results: The sampled blood volume was accurate with estimated volumes within <2% of the expected 20 μl. Recovery using impact-assisted extraction was 73-87% for MPA and 100% for tacrolimus and was hematocrit-independent for both analytes. The LC-MS/MS assay is precise and accurate within the acceptance criteria of 15%. Conclusion: The sampling and extraction procedures allowed for accurate quantification of tacrolimus and MPA. Exploration of abuse scenarios identified important education points for patients conducting home-based sample collections in the future.

Quantification of vincristine and tariquidar by LC-MS/MS in mouse whole blood using volumetric absorptive microsampling for pharmacokinetic applications

A liquid chromatography-tandem mass spectrometry method was developed and validated for the simultaneous quantification of vincristine and tariquidar in 10 μL of mouse whole blood using volumetric absorptive microsampling devices. Samples were extracted from the devices and quantified against calibrators prepared in a human blood plasma matrix. Separation of vincristine and tariquidar was achieved using a Shimpack XR ODS III C18 stationary phase and H₂ O and methanol mobile phase solvents containing 0.1% formic acid, running a gradient elution at a flow rate 0.2 mL/min over 6.0 min. The method was linear up to 1200 ng/mL (R² > 0.99 for both analytes), with calibrator accuracy within ± 15% of the nominal concentrations and analyte coefficient of variance < 15% for both vincristine and tariquidar. Pharmacokinetic assessment of both analytes was successfully applied in mice as both single agent therapy and combination therapy over a 24-hour period, and a 2.3-fold increase in vincristine drug exposure was observed in combination with tariquidar. This study validates the use of this approach for longitudinal analysis of drug exposure in animal studies. This article is protected by copyright. All rights reserved.

Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors Using Dried Blood Microsamples

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) is not yet performed routinely in the standard care of oncology patients, although it offers a high potential to improve treatment outcome and minimize toxicity. TKIs are perfect candidates for TDM as they show a relatively small therapeutic window, a wide inter-patient variability in pharmacokinetics and a correlation between drug concentration and effect. Moreover, most of the available TKIs are susceptible to various drug-drug interactions and medication adherence can be checked by performing TDM. Plasma, obtained via traditional venous blood sampling, is the standard matrix for TDM of TKIs. However, the use of plasma poses some challenges related to sampling and stability. The use of dried blood microsamples can overcome these limitations. Collection of samples via finger-prick is minimally invasive and considered convenient and simple, enabling sampling by the patients themselves in their home-setting. The collection of small sample volumes is especially relevant for use in pediatric populations or in pharmacokinetic studies. Additionally, working with dried matrices improves compound stability, resulting in convenient and cost-effective transport and storage of the samples. In this review we focus on the different dried blood microsample-based methods that were used for the quantification of TKIs. Despite the many advantages associated with dried blood microsampling, quantitative analyses are also associated with some specific difficulties. Different methodological aspects of microsampling-based methods are discussed and applied to TDM of TKIs. We focus on sample preparation, analytics, internal standards, dilution of samples, external quality controls, dried blood spot specific validation parameters, stability and blood-to-plasma conversion methods. The various impacts of deviating hematocrit values on quantitative results are discussed in a separate section as this is a key issue and undoubtedly the most widely discussed issue in the analysis of dried blood microsamples. Lastly, the applicability and feasibility of performing TDM using microsamples in a real-life home-sampling context is discussed.

Volumetric absorptive microsampling as a suitable tool to monitor tyrosine kinase inhibitors

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) shows significant potential in guiding personalized anticancer treatment. Dried blood microsampling could be a valuable alternative for traditional plasma sampling to provide TDM results faster and to reach a wider audience. Sample collection is easy and patient friendly as only a small volume of blood is collected via a fingerprick. This enables the possibility of home sampling by the patients themselves. Therefore, an LC-MS/MS method was developed and validated for the quantification of bosutinib, dasatinib, gilteritinib, ibrutinib, imatinib, midostaurin, nilotinib and ponatinib in dried blood samples collected via volumetric absorptive microsampling (VAMS). A VAMS device collects a fixed volume of blood (± 10 µL), irrespective of the sample's hematocrit (Hct). During method validation, special attention was paid to the possible impact of Hct (range 0.18-0.55) on matrix effect (ME), robustness of the extraction, and accuracy of the method. The method was successfully validated based on international guidelines in terms of calibration curves, precision (within-run CV 2.20-14.8%; between-run CV 2.40-12.3%), accuracy (within-run bias 0.34-12.5%; between-run bias -0.15 to 16.2%), carry-over and selectivity. IS-compensated ME and recovery were Hct independent and no significant impact of Hct on the accuracy of the TKI quantifications was observed. All TKIs were stable in VAMS samples stored at -20 °C, 4 °C and room temperature for at least 4 weeks and for 2 days at 60 °C (except ibrutinib). Lastly, we demonstrated a good agreement between liquid blood obtained from patients on TKI treatment and VAMS samples prepared from that venous blood. As this implies that there is no methodological impact of liquid versus dried blood analysis, the presented method can be applied in clinical follow-up studies for determining TKIs in (capillary) VAMS samples with varying Hct levels.

Determination of paracetamol and its metabolites via LC-MS/MS in dried blood volumetric absorptive microsamples: A tool for pharmacokinetic studies

Paracetamol (acetaminophen, APAP) is the most frequently used analgesic and antipyretic worldwide. Nonetheless, APAP induced hepatotoxicity is the most common cause of acute liver failure in the western world. This hepatotoxicity is related to the metabolism of APAP, via the formation of the electrophilic oxidation product N-acetyl-para-benzoquinone imine. To investigate differences in APAP metabolism in specific patient populations and to optimize dosing regimens, quantification of metabolites from the different metabolic pathways is needed to perform pharmacokinetic (PK) studies. For this purpose, sensitive and short liquid chromatography-tandem mass spectrometry methods were developed for the quantitation of APAP and four of its metabolites (APAP-glucuronide, APAP-sulfate, APAP-mercapturate, and APAP-cysteine) in plasma, whole blood and dried blood microsamples collected via 10 µL volumetric absorptive microsampling (VAMS) devices. The methods were successfully validated based on internationally accepted guidelines (EMA, FDA), encompassing selectivity, evaluation of the calibration model, matrix effect and recovery, accuracy and precision, stability, and dilution integrity. In addition, for the VAMS samples, the effect of the hematocrit on the recovery was evaluated. Successful application on whole blood and plasma, as well as on VAMS samples prepared from venous or capillary blood of patients, demonstrated that the methods were fit-for-purpose and can be used for future PK studies.

Review of the Preanalytical Errors That Impact Therapeutic Drug Monitoring

PURPOSE

Preanalytical errors comprise the majority of testing errors experienced by clinical laboratories and significantly impact the accuracy of therapeutic drug monitoring (TDM).

METHODS

Specific preanalytical factors in sample timing, collection, transport, processing, and storage that lead to errors in TDM were reviewed. We performed a literature search using several scientific databases including PubMed, ScienceDirect, Scopus, Web of Science, and ResearchGate for human studies published in the English language from January 1980 to February 2021, reporting on TDM and the preanalytical phase.

RESULTS

Blood collection errors (ie, wrong anticoagulant/clot activator used, via an intravenous line, incorrect time after dosing) delay testing, cause inaccurate results, and adversely impact patient care. Blood collected in lithium heparin tubes instead of heparin sodium tubes produce supertoxic lithium concentrations, which can compromise care. Specimens collected in serum separator gel tubes cause falsely decreased concentrations due to passive absorption into the gel when samples are not processed and analyzed quickly. Dried blood spots are popular for TDM as they are minimally invasive, allowing for self-sampling and direct shipping to a clinical laboratory using regular mail. However, blood collection techniques, such as trauma to the collection site, filter paper fragility, and hematocrit (Hct) bias, can adversely affect the accuracy of the results. Volumetric absorptive microsampling is a potential alternative to dried blood spot that offers fast, volume-fixed sampling, low pain tolerance, and is not susceptible to Hct concentrations.

CONCLUSIONS

The identification of preanalytical factors that may negatively impact TDM is critical. Developing workflows that can standardize TDM practices, align appropriate timing and blood collection techniques, and specimen processing will eliminate errors.

Microsampling Devices for Routine Therapeutic Drug Monitoring-Are We There Yet?

BACKGROUND

The use of microsampling for therapeutic drug monitoring (TDM) is increasingly feasible as sensitive methods have become more accessible. There exists an increasing interest in the use of microsampling, and new microsampling devices and techniques can potentially improve patient convenience and care, among other features. This review provides an update on currently validated methods for measuring drugs pertinent to TDM, including data from clinical samples.

METHODS

A literature record search was undertaken, including PubMed and Google Scholar. Reports that included the use of microsampling to measure concentrations of drugs associated with TDM were reviewed and included if data from patient samples were reported. The studies are described in brief, including sample preparation and analyte stability, with the most pertinent findings reported.

RESULTS

Sensitive analyses and innovative designs and materials have resulted in an increasing number of reported evaluations and validations for measuring drugs using microsamples. Novel designs largely overcome common problems associated with traditional dried blood spot sampling. Although examples of patient self-sampling are rare at present, studies that evaluated feedback found it to be largely positive, revealing the feasibility of microsampling for TDM.

CONCLUSIONS

Microsampling is suited to the TDM of numerous drugs in diverse situations, and it will play an increasingly important role. The issues with traditional dried blood spot samples have been largely overcome by employing novel methods to obtain volumetric samples.

Addressing New Possibilities and New Challenges: Automated Nondestructive Hematocrit Normalization for Dried Blood Spots

ABSTRACT

The patient's hematocrit (HCT) level can adversely affect the analysis results when dried blood spots (DBS) are used for sampling. Volumetric DBS sampling has been proposed to nullify the impact of HCT area bias (spreading area) on DBS by normalizing to a known sample volume. However, this strategy ignores DBS-related parameters such as analyte properties (red blood cell-to-plasma ratio) and HCT recovery bias. With the recent release of fully automated HCT measurement systems for DBS analysis, a broad range of end users are now able to measure and correct a sample's HCT level in a nondestructive manner. These systems permit correction for all known HCT-related impacts on DBS, such as analyte properties, HCT recovery bias, HCT area bias, and venous blood-to-DBS ratio, supporting and accelerating future quantitative DBS applications. However, with these novel tools, new questions arise concerning the normalization of analytical results, the choice of technique (single-wavelength reflectance vs near-infrared spectroscopy), and the DBS card-handling process post sampling. Herein, the necessary considerations for end users are addressed and examples are provided.

Alternative Sampling Devices to Collect Dried Blood Microsamples: State-of-the-Art

ABSTRACT

Dried blood spots (DBS) have been used in newborn screening programs for several years. More recently, there has been growing interest in using DBS as a home sampling tool for the quantitative determination of analytes. However, this presents challenges, mainly because of the well-known hematocrit effect and other DBS-specific parameters, including spotted volume and punch site, which could add to the method uncertainty. Therefore, new microsampling devices that quantitatively collect capillary dried blood are continuously being developed. In this review, we provided an overview of devices that are commercially available or under development that allow the quantitative (volumetric) collection of dried blood (-based) microsamples and are meant to be used for home or remote sampling. Considering the field of therapeutic drug monitoring (TDM), we examined different aspects that are important for a device to be implemented in clinical practice, including ease of patient use, technical performance, and ease of integration in the workflow of a clinical laboratory. Costs related to microsampling devices are briefly discussed, because this additionally plays an important role in the decision-making process. Although the added value of home sampling for TDM and the willingness of patients to perform home sampling have been demonstrated in some studies, real clinical implementation is progressing at a slower pace. More extensive evaluation of these newly developed devices, not only analytically but also clinically, is needed to demonstrate their real-life applicability, which is a prerequisite for their use in the field of TDM.

Tacrolimus Area Under the Concentration Versus Time Curve Monitoring, Using Home-Based Volumetric Absorptive Capillary Microsampling

BACKGROUND

Therapeutic drug monitoring (TDM) of tacrolimus (Tac) is mandatory in renal transplant recipients (RTxR). Area under the concentration versus time curve (AUC) is the preferred measure for Tac exposure; however, for practical purposes, most centers use trough concentrations as a clinical surrogate. Limited sampling strategies in combination with population pharmacokinetic model-derived Bayesian estimators (popPK-BE) may accurately predict individual AUC. The use of self-collected capillary microsamples could simplify this strategy. This study aimed to investigate the potential of AUC-targeted Tac TDM using capillary microsamples in combination with popPK-BE.

METHODS

A single-center prospective pharmacokinetic study was conducted in standard-risk RTxR (n = 27) receiving Tac twice daily. Both venous and capillary microsamples (Mitra; Neoteryx, Torrance, CA) were obtained across 2 separate 12-hour Tac dosing intervals (n = 13 samples/AUC). Using popPK-BE, reference AUC (AUCref) was determined for each patient using all venous samples. Different limited sampling strategies were tested for AUC predictions: (1) the empiric sampling scheme; 0, 1, and 3 hours after dose and (2) 3 sampling times determined by the multiple model optimal sampling time function in Pmetrics. Agreement between the predicted AUCs and AUCref were evaluated using C-statistics. Accepted agreement was defined as a total deviation index ≤±15%.

RESULTS

The AUC from capillary microsamples revealed high accuracy and precision compared with venous AUCref, and 85% of the AUCs had an error within ±11.9%. Applying microsamples at 0, 1, and 3 hours after dose predicted venous AUCref with acceptable agreement. Patients performed self-sampling with acceptable accuracy.

CONCLUSIONS

Capillary microsampling is patient-centered, making AUC-targeted TDM of Tac feasible without extended hospital stays. Samples obtained 0, 1, and 3 hours after dose, combined with popPK-BE, accurately predict venous Tac AUC.

Dried blood spots in doping analysis

A series of dried blood spot (DBS) detection methods for doping agents have been developed in the last two decades. The DBS technique minimizes invasiveness and reduces storage and shipping costs. Recently, the World Anti-Doping Agency announced the use of DBS for the 2022 Beijing Winter Olympic Games and Paralympic Games owing to the advantages of the DBS application in routine doping control. Therefore the further development of detection methods for doping agents in DBS is important and urgent. This review summarizes five aspects of DBS application in doping analysis: sample collection, storage conditions, pretreatment, instrumentation and validation according to the Prohibited List issued by the World Anti-Doping Agency, and proposes some suggestions for future studies of DBS in doping analysis.

Volumetric absorptive microsampling as alternative sampling technique for renal function assessment in the paediatric population using iohexol

The glomerular filtration rate (GFR) is considered the best overall index for the renal function. Currently, one of the most promising exogenous markers for GFR assessment is iohexol. In this study, the suitability of volumetric absorptive microsampling (VAMS) as alternative for the conventional blood sampling and quantification of iohexol in paediatric plasma was assessed. Therefore, a new, fully validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed. Subsequently, the clinical suitability was evaluated in 20 paediatric patients by comparing plasma iohexol concentrations and associated GFR values obtained by the VAMS method with those obtained by conventional blood sampling and quantification of iohexol in plasma. The developed, simple and cost-effective LC-MS/MS-method fulfilled all pre-set validation acceptance criteria. Iohexol could be accurately quantified within a haematocrit range of 20-60% and long-term stability of iohexol in VAMS was demonstrated up to 245 days under different storage temperatures. Both iohexol plasma concentrations (r = 0.98, mean bias: -4.20%) and derived GFR values (r = 0.99; mean bias: 1.31%), obtained by a conventional plasma and the VAMS method, demonstrated good correlation and acceptable bias. The agreement between the two methods was especially good for GFR values higher than 60 mL/min/1.73 m². Nevertheless, for GFR values <60 mL/min/1.73 m² the accuracy compared to the plasma method was lower. However, small adjustments to the sampling protocol could probably solve this problem.

Volumetric absorptive microsampling (VAMS®) in therapeutic protein quantification by LC-MS/MS: Investigation of anticoagulant impact on assay performance and recommendations for best practices in method development

Microsampling techniques have been employed as an alternative to traditional serum/plasma sampling because of their inherently proven and desirable advantages across the pharmaceutical industry. These include reduced animal usage in pre-clinical studies, as well as, permitting the collection of samples that would otherwise be inaccessible in clinical studies. The application of volumetric absorptive microsampling (VAMS®) technology, a second-generation dried microsampling method, coupled with LC-MS, has been extensively explored for small molecule drugs at various drug development stages. However, the potential of using VAMS technology and LC-MS analysis for biological therapeutic development has yet to be well-established. In this work, we describe the method development, validation, and a proof-of-concept non-human primate study of a LC-MS/MS method for VAMS utilized to obtain pharmacokinetic (PK) data for a therapeutic monoclonal antibody. A good correlation between VAMS data and data from conventional serum samples was established in rhesus monkeys and indicated the possibility of using of this novel sampling technology in clinical studies. However, during the initial clinical study, a significant difference in internal standard (IS) response between the patient fingerstick samples and the standard/QC samples was observed, which posed a question on the accuracy of the clinical results. A comprehensive investigation confirmed that the EDTA anticoagulant used in the standard/QC samples was the root cause of the observed anomalous IS responses. Special considerations and corresponding best practices during method development and validation are proposed to ensure early detection of potential issues and appropriate implementation of VAMS technology in clinical studies in the future.

Volumetric Absorptive Microsampling as a Sampling Alternative in Clinical Trials and Therapeutic Drug Monitoring During the COVID-19 Pandemic: A Review

An infectious disease, COVID-19, caused by a new type of coronavirus, has been discovered recently. This disease can cause respiratory distress, fever, and fatigue. It still has no drug and vaccine for treatment and prevention. Therefore, WHO recommends that people should stay at home to reduce disease transmission. Due to the quarantine, FDA stated that this could hamper drug development clinical trial protocols. Hence, an alternative sampling method that can be applied at home is needed. Currently, volumetric absorptive microsampling (VAMS) has become attention in its use in clinical and bioanalytical fields. This paper discusses the advantages and challenges that might be found in the use of VAMS as an alternative sampling tool in clinical trials and therapeutic drug monitoring (TDM) during the COVID-19 pandemic. VAMS allows easy sampling, can be done at home, storage and delivery at room temperature, and the volume taken is small and minimally invasive. VAMS is also able to absorb a fixed volume that can increase the accuracy and precision of analytical methods, and reduce the hematocrit effects (HCT). The use of VAMS is expected to be implemented immediately in clinical trials and TDM during this pandemic considering the benefits it has.

Quantitative and qualitative application of a novel capillary microsampling device, Microsampling Wing™ (MSW), using antiepileptic drugs in rats

A novel microsampling device, namely, the Microsampling Wing™ (MSW), was evaluated using three anti-epileptic drugs (AEDs): carbamazepine, lamotrigine, and phenytoin. A simultaneous assay method of the three AEDs was developed and qualified via liquid chromatography with tandem mass spectrometry. Using 2.8 μL plasma, the three AEDs were quantifiable from 1 or 2 ng/mL. According to the intra-assay reproducibility assessment and additional validation parameters, the established method is reproducible. To apply the device to a pharmacokinetic (PK) study in rats, a cocktail of the three AEDs was orally administered to rats. Whole blood samples were serially collected using the MSW device and a glass capillary from the tail vein, and plasma samples (each 2.8 μL) from each device were assayed to compare PK parameters. The PK parameters of the three AEDs were similar between the two devices. A metabolite identification study was also conducted after oral administration of carbamazepine to rats. At least seven metabolites were detected in plasma, and the major metabolite was carbamazepine 10,11-epoxide, which is in accordance with the reported results. These findings suggest that the MSW device is a useful microsampling device for PK and metabolite identification studies.

Dried blood spots for anti-doping: Why just going volumetric may not be sufficient

The perspective discusses quantitative DBS analysis for anti-doping testing in an athletic population and why only using volumetric sampling for this subgroup might not be enough. It presents examples to highlight where HCT variations occur, followed by a whole blood to plasma ratio and an HCT extraction bias discussion. Finally, options to correct for the HCT bias are presented.

A Volumetric Absorptive Microsampling Technique to Monitor Cannabidiol Levels in Epilepsy Patients

Purpose: Interest in cannabis-based therapies has recently increased, due to the availability of cannabidiol (CBD) for the treatment of epilepsy without psychoactive effects. Therapeutic drug monitoring can prevent drug interactions and minimize drug toxicity. We evaluated a volumetric absorptive microsampling (VAMS) method combined with LC-MS/MS (liquid chromatography coupled to tandem mass spectrometry) for the quantification of CBD blood levels in patients with refractory epilepsy.

Methods: Prospective observation of patients with Dravet syndrome receiving open-label, add-on GW-purified CBD (Epidyolex^®) at different doses. CBD plasma samples were obtained from venipuncture and LC-MS/MS was used to measure CBD in venous and capillary blood samples collected by VAMS.

Results: We enrolled five patients with a mean age of 13 (range: 4–27) years. CBD levels measured by VAMS on capillary blood did not differ from CBD levels measured in plasma by venipuncture (R² > 0.93).

Conclusion: This proof-of-concept study suggests that VAMS allows monitoring of CBD plasma levels and can offer valuable support for personalized therapy in refractory epilepsy.

Analysis of 14 drugs in dried blood microsamples in a single workflow using whole blood and serum calibrators

Aim: Multiplexed, high-throughput analysis facilitates therapeutic drug monitoring. 14 drugs with various physico-chemical properties were quantitated in dried blood microsamples. Methods: Analytes were extracted employing eight solvent compositions and seven extraction methods. The applicability of liquid serum, dried serum and dried whole blood calibrators was investigated. Results: High recoveries were attained. Calibration using dried serum yielded lowest total error. Reducing sample hematocrit caused outstanding elevations in recovery of analytes with high polarity or affinity to erythrocytes. 9-day analyte stability was demonstrated. Conclusion: Based on the analysis of spiked samples, multiplexed testing of drugs in dried blood microsamples seems feasible, but with analyte-dependent method performance. Dried serum calibration allows the adaptation of serum-based workflows. Further evaluation using real-life specimens is needed.

Cannabidiol Determination on Peripheral Capillary Blood Using a Microsampling Method and Ultra-High-Performance Liquid Chromatography Tandem Mass Spectrometry with On-Line Sample Preparation

The aim of this work is to evaluate volumetric absorptive microsampling (VAMS) from capillary blood as an alternative strategy for therapeutic drug monitoring (TDM) in patients treated with the newly available GW-purified form of cannabidiol (Epidiolex^®). A fast ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) coupled to an online sample preparation system analysis was carried out on a Thermo Scientific Ultimate 3000 LC system coupled to a TSQ Quantiva triple quadrupole for the quantification of cannabidiol (CBD) and, in addition, delta-9-tetrahydrocannabinol (Δ9-THC). After validation using European Medicine Agency (EMA) guidelines the method was applied to samples obtained by finger prick of five pediatric patients treated with Epidiolex^® and the results were compared to those obtained from venous blood and plasma. The method is linear in the range of 1–800 µg/L for both CBD and THC with intra- and inter-day precisions ranging from 5% to 14% and accuracies from −13% to +14% starting from 30 µL of sample. Stability in VAMS is ensured for up to 4 weeks at 25 °C thus allowing simple delivery. There was no difference (p = 0.69) between concentrations of CBD measured from VAMS sampled from capillary or venous blood (range: 52.19–330.14 or 72.15–383.45 µg/L) and those obtained from plasma (range: 64.3–374.09 µg/L) The VAMS-LC-MS/MS method represents a valid alternative strategy for therapeutic drug monitoring of patients treated with Epidiolex^®.

Validation and clinical application of a volumetric absorptive microsampling method for 14 psychiatric drugs

Aim: Volumetric absorptive microsampling offers a hematocrit insensitive way for microsampling. The aim of this study was to develop a method for routine healthcare for 14 antidepressants, antipsychotics and their active metabolites on a single-quadrupole HPLC–MS. A clinical validation study to determine conversion factors from capillary blood to plasma concentration was conducted afterward. Results: The method was validated according to current guidelines except for one substance. Five substances were measured in 49 patient samples and conversion factors could be derived with Passing–Bablok and Bland–Altman analysis. Conclusion: A reliable extraction and analysis method for commonly used antidepressants and antipsychotics was developed and validated. The method with the obtained conversion factors can now be used in routine healthcare.

Volumetric Absorptive Microsampling: A New Sampling Tool for Therapeutic Drug Monitoring of Antiepileptic Drugs

BACKGROUND

Volumetric absorptive microsampling (VAMS) is a novel sampling technique for the collection of fixed-volume capillary blood. In this study, a new analytical method was developed and used to quantify 14 different antiepileptic drugs (AEDs) and 2 active metabolites in samples collected by VAMS. These data were compared with concentration measurements in plasma.

METHODS

The authors developed a selective and sensitive liquid chromatography-mass spectrometry (LC-MS/MS) assay to measure the concentrations of several AEDs in whole blood collected by VAMS, which were compared with a commercially available LC-MS/MS kit for AED monitoring in plasma. Drugs and internal standards were extracted from whole blood/plasma samples by a simple protein precipitation.

RESULTS

An LC-MS/MS method analyzing VAMS samples was successfully developed and validated for the determination of various AED concentrations in whole blood according to EMA guidelines for bioanalytical method validation. Extraction recovery was between 91% and 110%. No matrix effect was found. The method was linear for all drugs with R ≥0.989 in all cases. Intra-assay and inter-assay reproducibility analyses demonstrated accuracy and precision within acceptance criteria. Carry over and interferences were negligible. No volumetric HCT% bias was found at 3 different HCT values (35%-55%) with recovery being consistently above 87%. Samples are very stable at temperatures ranging from -20°C to 37°C and for a 4-month period. Leftover EDTA samples from 133 patients were tested to determine concentration differences between plasma and whole blood sampled by VAMS. The resulting difference varied less than 15% apart from those drugs with a blood/plasma ratio (R) different from 1.

CONCLUSIONS

The assay allows for highly sensitive and selective quantification of several AEDs in whole blood samples collected by VAMS. The developed method is accurate and precise and free from matrix effects and volumetric HCT% bias.

Official International Association for Therapeutic Drug Monitoring and Clinical Toxicology Guideline: Development and Validation of Dried Blood Spot-Based Methods for Therapeutic Drug Monitoring

Dried blood spot (DBS) analysis has been introduced more and more into clinical practice to facilitate Therapeutic Drug Monitoring (TDM). To assure the quality of bioanalytical methods, the design, development and validation needs to fit the intended use. Current validation requirements, described in guidelines for traditional matrices (blood, plasma, serum), do not cover all necessary aspects of method development, analytical- and clinical validation of DBS assays for TDM. Therefore, this guideline provides parameters required for the validation of quantitative determination of small molecule drugs in DBS using chromatographic methods, and to provide advice on how these can be assessed. In addition, guidance is given on the application of validated methods in a routine context. First, considerations for the method development stage are described covering sample collection procedure, type of filter paper and punch size, sample volume, drying and storage, internal standard incorporation, type of blood used, sample preparation and prevalidation. Second, common parameters regarding analytical validation are described in context of DBS analysis with the addition of DBS-specific parameters, such as volume-, volcano- and hematocrit effects. Third, clinical validation studies are described, including number of clinical samples and patients, comparison of DBS with venous blood, statistical methods and interpretation, spot quality, sampling procedure, duplicates, outliers, automated analysis methods and quality control programs. Lastly, cross-validation is discussed, covering changes made to existing sampling- and analysis methods. This guideline of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology on the development, validation and evaluation of DBS-based methods for the purpose of TDM aims to contribute to high-quality micro sampling methods used in clinical practice.

Validation of methods for determining pediatric midazolam using wet whole blood and volumetric absorptive microsampling

Aim: Collection and quantitative analysis in dry blood using volumetric absorptive microsampling (VAMS™) potentially offers significant advantages over conventional wet whole blood analysis. This manuscript explores their use for pediatric sampling and explores additional considerations for the validation of the bioanalytical method. Results: HPLC–MS/MS methods for the determination of midazolam and its major metabolite 1-OH midazolam in both whole wet blood, and dry blood collected on VAMS were developed, validated, and used to support an observational clinical study to compare pharmacokinetic parameters in pediatric patients. Conclusion: Validation data met internationally accepted guideline criteria. A strong correlation was observed in calculated concentrations between wet and dry test samples, indicating that VAMS is a suitable technique for use in pediatric clinical studies.

A review of microsampling techniques and their social impact

Conventional skin and blood sampling techniques for disease diagnosis, though effective, are often highly invasive and some even suffer from variations in analysis. With the improvements in molecular detection, the amount of starting sample quantity needed has significantly reduced in some diagnostic procedures, and this has led to an increased interest in microsampling techniques for disease biomarker detection. The miniaturization of sampling platforms driven by microsampling has the potential to shift disease diagnosis and monitoring closer to the point of care. The faster turnaround time for actionable results has improved patient care. The variations in sample quantification and analysis remain a challenge in the microsampling field. The future of microsampling looks promising. Emerging techniques are being clinically tested and monitored by regulatory bodies. This process is leading to safer and more reliable diagnostic platforms. This review discusses the advantages and disadvantages of current skin and blood microsampling techniques.

Application of a Volumetric Absorptive Microsampling Device to a Pharmacokinetic Study of Tacrolimus in Rats: Comparison with Wet Blood and Plasma

BACKGROUND AND OBJECTIVES

Volumetric absorptive microsampling (VAMS) devices are useful for sampling a smaller volume of blood from rodents in the preclinical setting. In the present study, we evaluated the proof of concept of a VAMS device by comparing the pharmacokinetic data of tacrolimus in rats among dried blood in VAMS, wet blood, and plasma.

METHODS

Tacrolimus was administered orally, to rats, at a dose of 10 mg/kg. Only 10 μL aliquots of blood were absorbed by VAMS devices at designated time points. Tacrolimus was extracted with a methanol-water mixture (1:1, v/v) via sonication. Tacrolimus levels in wet blood (10 μL) and plasma (10 μL) were quantified after protein precipitation.

RESULTS

Tacrolimus in VAMS devices was quantifiable from 0.2 ng/mL using high-performance liquid chromatography with tandem mass spectrometer. Accuracy and precision were within the acceptance criteria. Bland-Altman plots showed that tacrolimus concentrations in VAMS devices were similar to those in wet blood, regardless of tacrolimus levels. On the other hand, tacrolimus levels in plasma were different from those in VAMS devices, especially at lower concentrations, likely due to partition of tacrolimus to blood cells. However, pharmacokinetic parameters were comparable among the three matrices.

CONCLUSIONS

Collectively, these findings suggest that the VAMS device can be a useful device for pharmacokinetic studies in rats.

A volumetric absorptive microsampling LC–MS/MS method for five immunosuppressants and their hematocrit effects

Aim: The aim of this study was to develop and validate a LC–MS/MS assay for tacrolimus, sirolimus, everolimus, cyclosporin A and mycophenolic acid using volumetric absorptive microsampling tips as a sampling device and to investigate the effect on the recoveries of the analyte concentration in combination with the hematocrit (HT), which included temsirolimus (a structural analog). Results: The maximum observed overall bias was 9.6% for the sirolimus LLOQ, while the maximum overall coefficient of variation was 8.3% for the everolimus LLOQ. All five immunosuppressants demonstrated to be stable in the volumetic absorbtive microsampling tips for at least 14 days at 25°C. Biases caused by HT effects were within 15% for all immunosuppressants between HT levels of 0.20 and 0.60 l/l, except for cyclosporin A, which was valid between 0.27 and 0.60 l/l. Reduced recoveries were observed at high analyte concentrations in combination with low HT values for sirolimus, everolimus and temsirolimus. Conclusion: A robust extraction and analysis method in volumetric absorptive microsampling tips was developed and fully validated. HT- and concentration-related recovery effects were observed but were within requirements of the purpose of the analytical method.

Application of Mitra® microsampling for pharmacokinetic bioanalysis of monoclonal antibodies in rats

Aim: Volumetric absorptive microsampling (VAM) is being increasingly applied in nonclinical pharmacokinetic studies. Although there are published results for VAM use in small molecule pharmacokinetics (PK) studies, there is limited data on the utility of VAM for protein therapeutics. Results: We describe the use of Mitra® microsampler for blood sampling, ELISA quantitation and PK analysis of two marketed therapeutic monoclonal antibodies administered to rat. Results generated for these monoclonal antibodies using Mitra® were compared with both serum and whole blood sampling methods in the same study. Conclusion: The low relative standard deviation among the three sets of PK data suggest that Mitra® microsampler could be useful in early nonclinical PK studies for protein therapeutics where reduction and refinement of animal use is desirable.

Volumetric absorptive microsampling (VAMS) coupled with high-resolution, accurate-mass (HRAM) mass spectrometry as a simplified alternative to dried blood spot (DBS) analysis for therapeutic drug monitoring of cardiovascular drugs

Here, volumetric absorptive microsampling (VAMS), used for the measurement of cardiovascular drugs, is compared against conventional dried blood spot (DBS) card sampling to evaluate adherence to prescribed medication. Volumetric absorptive microsampling (VAMS) is an attractive alternative to plasma sampling for routine drug monitoring and potentially overcomes haematocrit issues associated with quantitative bioanalysis of conventional dried blood spots. A quantitative VAMS-based LC-HRAM MS assay for atenolol, lisinopril, simvastatin and valsartan was developed and validated. The assay demonstrated acceptable linearity, selectivity, accuracy, precision, recovery and insignificant matrix effects with no impact of haematocrit on assay accuracy. Volunteers provided both VAMS and DBS 903 card samples (the current standard) to allow comparison of the two methods and demonstrate the potential utility of VAMS. Analysis of VAMS samples correctly identified drugs in volunteers known to be adherent, and found no false positives from volunteers known to be taking no medication. There was a strong correlation between the two sampling systems confirming the utility of VAMS. Therapeutic drug monitoring (TDM) can assist clinicians in deciding how to proceed with treatment in the event of poor improvement in patient health. VAMS could offer a potentially more efficient method of sample collection, with fewer rejected samples than the DBS approach.

Tutorial: Volumetric absorptive microsampling (VAMS)

Volumetric absorptive microsampling (VAMS) is a recent microsampling technique used to obtain dried specimens of blood and other biological matrices for application to a plethora of bioanalytical purposes. As such, it can be likened to dried blood spot (DBS) technique that has been in wide use for the last 40 years. However, VAMS promises to bring some significant advantages over DBS, related to sampling volume accuracy, haematocrit (HCT) dependence, pre-treatment and automation. Although some aspects still need to be investigated in depth, VAMS is increasingly recognised as a viable alternative to DBS and other dried microsampling techniques. In this tutorial, different aspects of VAMS approach are described and discussed, presenting the procedures adopted and the results obtained by those authors who have developed this kind of analytical workflow in the last few years. Hopefully, this will help other scientists to find new solutions to old and recent problems related to microsampling and to produce new, sound and interesting science in this field.

Extractability-mediated stability bias and hematocrit impact: High extraction recovery is critical to feasibility of volumetric adsorptive microsampling (VAMS) in regulated bioanalysis

Volumetric absorptive microsampling (VAMS), a new microsampling technique, was evaluated for its potential in supporting regulated bioanalysis. Our initial assessment with MK-0518 (raltegravir) using a direct extraction method resulted in 45-52% extraction recovery, significant hematocrit (Ht) related bias, and more importantly, unacceptable stability (>15% bias from nominal concentration) after 7-day storage. Our investigation suggested that the observed biases were not due to VAMS absorption, sampling techniques, lot-to-lot variability, matrix effect, and/or chemical stability of the compound, but rather the low extraction recovery. An effort to improve assay recovery led to a modified liquid-liquid extraction (LLE) method that demonstrated more consistent performance, minimal Ht impact (Ht ranged from 20 to 65%), and acceptable sample stability. The same strategy was successfully applied to another more hydrophilic model compound, MK-0431 (sitagliptin). These results suggest that the previously observed Ht effect and "instability" were in fact due to inconsistent extractability, and optimizing the extraction recovery to greater than 80% was critical to ensure VAMS performance. We recommend adding Ht-independent recovery as part of feasibility assessment to de-risk the long-term extractability-mediated stability bias before implementing VAMS in regulated bioanalysis.

Quantitative analysis of acetylsalicylic acid in human blood using volumetric absorptive microsampling

Volumetric absorptive microsampling (VAMS) is a novel sampling technique that allows for the collection of an accurate volume of blood by dipping a microsampler tip. The purpose of this study is to compare the requirement of a stabilizing reagent for the conventional venous blood sampling method versus VAMS in the analytical measurement of the concentration of acetylsalicylic acid. A high-performance liquid chromatography with mass spectrometry (LC-MS/MS) method was developed and validated for the accurate determination of acetylsalicylic acid in human blood. The blood samples spiked with acetylsalicylic acid with and without stabilizing reagent were absorbed into VAMS tips. In the whole blood sample, the same concentration was shown regardless of the addition of the stabilizing reagent, but the concentration decreased when the stabilizing reagent was not added to the VAMS sample. To apply the VAMS technology as a new blood sampling method, stabilizing reagents should be added before the analysis of acetylsalicylic acid concentration.