Volumetric absorptive microsampling as an alternative tool for therapeutic drug monitoring of first-generation anti-epileptic drugs

Development of LC-MS/MS method for quantification of Lurasidone using volumetric absorptive microsampling (VAMS); a comparative study between dried blood and plasma samples

The ecological impact of biological, chemical, and analytical research practices, including toxic reagents and biohazardous waste, has led to the development of alternative sampling and extraction techniques for bioanalysis. Microsampling (sample volume < 50 µL) aligns with the 3Rs principle, allowing multiple sampling points from the same animal at different time points and improving animal welfare. A bioanalytical method was developed to investigate factors related to bioanalytical challenges and the implementation of microsampling techniques. An LC-MS/MS method for Volumetric Absorptive Microsampling (VAMS), 20 µL, was developed for quantifying Lurasidone using a liquid-liquid extraction technique. The method uses a C18, Phenomenex column for chromatographic separation and a mobile phase composition of Methanol, Acetonitrile, and Water with 0.1 % HFBA. The method was validated over a concentration range of 5.0 to 1200.0 ng/mL and achieved acceptable precision and accuracy. The recovery for analyte from VAMS was approximately 40% at four different concentrations and is consistent (%CV < 15), with no significant differences among HCT levels. The matrix factor ranged between 85.00 and 115.00 %, showing no substantial issues with reduced or enhanced signal. The stability data showed no significant degradation of LUR in VAMS samples when stored at room temperature for 15 days. The newly established method for Lurasidone confirmed the use of VAMS sampling method and its analysis on LC-MS/MS. Further, the data obtained from microsampling techniques was compared with conventional (plasma) technique, as proof-of-concept, and it confirms the agreement between the two methods. The study supports the advantages of microsampling in protecting the environment and animals while maintaining scientific judgement.

Fingerprick volumetric absorptive microsampling for therapeutic drug monitoring of antiseizure medications: Reliability and real-life feasibility in epilepsy patients

Volumetric absorptive microsampling (VAMS) is increasingly proposed as a clinically reliable therapeutic drug monitoring (TDM) sampling methodology. The study aimed to establish the reliability and real-life feasibility of patient self-collected capillary VAMS for TDM of antiseizure medication (ASMs), using plasma ASMs concentrations from venous blood as a reference standard. Nurses collected venous and capillary blood samples using VAMS. Afterward, persons with epilepsy (PWE) performed VAMS sampling by themselves. All samples were analyzed by UHPLC-MS/MS. We performed a cross-validation study, comparing ASMs concentrations obtained by VAMS nurses and patients' self-collected versus plasma through Bland-Altman analysis and Passing-Bablok regression. We enrolled 301 PWE (M: F 42.5%:57.5%; mean age 44±16 years), treated with 13 ASMs, providing a total of 464 measurements. Statistical analysis comparing VAMS self-collected versus plasma ASMs concentrations showed a bias close to zero and slope and intercept values indicating a good agreement for CBZ, LCS, LEV, LTG, OXC, PB, and PHT, while a systematic difference between the two methods was found for VPA, PMP, TPM and ZNS. This is the first study showing the reliability and feasibility of the real-world application of PWE self-collected VAMS for most of the ASMs considered, giving a promising basis for at-home VAMS applications.

Proteome profiling of home-sampled dried blood spots reveals proteins of SARS-CoV-2 infections

BACKGROUND

Self-sampling of dried blood spots (DBS) offers new routes to gather valuable health-related information from the general population. Yet, the utility of using deep proteome profiling from home-sampled DBS to obtain clinically relevant insights about SARS-CoV-2 infections remains largely unexplored.

METHODS

Our study involved 228 individuals from the general Swedish population who used a volumetric DBS sampling device and completed questionnaires at home during spring 2020 and summer 2021. Using multi-analyte COVID-19 serology, we stratified the donors by their response phenotypes, divided them into three study sets, and analyzed 276 proteins by proximity extension assays (PEA). After normalizing the data to account for variances in layman-collected samples, we investigated the association of DBS proteomes with serology and self-reported information.

RESULTS

Our three studies display highly consistent variance of protein levels and share associations of proteins with sex (e.g., MMP3) and age (e.g., GDF-15). Studying seropositive (IgG+) and seronegative (IgG-) donors from the first pandemic wave reveals a network of proteins reflecting immunity, inflammation, coagulation, and stress response. A comparison of the early-infection phase (IgM+IgG-) with the post-infection phase (IgM-IgG+) indicates several proteins from the respiratory system. In DBS from the later pandemic wave, we find that levels of a virus receptor on B-cells differ between seropositive (IgG+) and seronegative (IgG-) donors.

CONCLUSIONS

Proteome analysis of volumetric self-sampled DBS facilitates precise analysis of clinically relevant proteins, including those secreted into the circulation or found on blood cells, augmenting previous COVID-19 reports with clinical blood collections. Our population surveys support the usefulness of DBS, underscoring the role of timing the sample collection to complement clinical and precision health monitoring initiatives.

Overview of therapeutic drug monitoring and clinical practice

With the rapid development of clinical pharmacy in China, therapeutic drug monitoring (TDM) has become an essential tool for guiding rational clinical drug use and is widely concerned. TDM is a tool that combines pharmacokinetic and pharmacodynamic knowledge to optimize personalized drug therapy, which can improve treatment outcomes, reduce drug-drug toxicity, and avoid the risk of developing drug resistance. To effectively implement TDM, accurate and sophisticated analytical methods are required. By researching the literature published in recent years, we summarize the types of commonly monitored drugs, therapeutic windows, and clinical assays and track the trends and hot spots of therapeutic drug monitoring. The purpose is to provide guidelines for clinical blood drug concentration monitoring, to implement individualized drug delivery programs better, to ensure the rational use of drugs for patients, and to provide a reference for the group to carry out related topics in the future.

Volumetric absorptive microsampling for the therapeutic drug monitoring of psychiatric patients treated with cariprazine

Psychiatric disorders are usually treated with antipsychotic agents belonging to different pharmacological and chemical classes, the most recent ones collectively known as "third-generation antipsychotics", such as cariprazine, approved in 2015 for the treatment of patients affected by schizophrenia. For these patients, a frequent therapeutic drug monitoring (TDM) becomes essential to assess compliance and to optimise and personalise their therapy, also due to cariprazine interindividual variability and narrow therapeutic range. In this study, a bioanalytical method featuring miniaturised sampling and pretreatment was developed, based on volumetric absorptive microsampling (VAMS) for TDM of psychiatric patients under cariprazine treatment and compared to a reference method based on fluid plasma analysis. Minimally invasive whole blood VAMS was coupled to an original instrumental method based on ultra-high performance liquid chromatography hyphenated to mass spectrometry (UHPLC-MS). A feasible and streamlined, yet reliable VAMS pretreatment protocol was carefully optimised and the VAMS-UHPLC-MS methodology was validated with satisfactory results in terms of linearity (r2 > 0.9970 in the 1.5-100 ng/mL range), precision (%RSD < 11.7), extraction yield (> 90.0 %) and matrix effect (8.2 ≤ %RE ≤ 10.9). Finally, the microsampling approach coupled to UHPLC-MS was successfully applied to the TDM of psychiatric patients treated with cariprazine and compared with standard fluid plasma analysis, providing reliable quali-quantitative results, and proving to be readily applicable to the clinical practice in TDM programs as a useful alternative to cariprazine plasma analysis. This is the first report of a successful microsampling application, and in particular the first report of VAMS application, for the TDM of cariprazine.

Therapeutic Drug Monitoring of Kinase Inhibitors in Oncology

Although kinase inhibitors (KI) frequently portray large interpatient variability, a 'one size fits all' regimen is still often used. In the meantime, relationships between exposure-response and exposure-toxicity have been established for several KIs, so this regimen could lead to unnecessary toxicity and suboptimal efficacy. Dose adjustments based on measured systemic pharmacokinetic levels-i.e., therapeutic drug monitoring (TDM)-could therefore improve treatment efficacy and reduce the incidence of toxicities. Therefore, the aim of this comprehensive review is to give an overview of the available evidence for TDM for the 77 FDA/EMA kinase inhibitors currently approved (as of July 1st, 2023) used in hematology and oncology. We elaborate on exposure-response and exposure-toxicity relationships for these kinase inhibitors and provide practical recommendations for TDM and discuss corresponding pharmacokinetic targets when possible.

Therapeutic Salivary Monitoring of Perampanel in Patients with Epilepsy Using a Volumetric Absorptive Microsampling Technique

The objective of this study was to validate a novel assay using the volumetric absorptive microsampling (VAMS) technique combined with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) for the determination of the antiseizure medication perampanel in saliva and its clinical applicability in patients with epilepsy. VAMS tips were loaded with 30 μL of saliva and dried for 60 min. Analytes were extracted with methanol. The supernatant was evaporated under a gentle stream of nitrogen and reconstituted with 60 μL of methanol. Separation and quantification were achieved on a monolithic column connected to a mass spectrometer. Calibration curves were linear between 0.5 and 300 ng/mL. Intra- and inter-day accuracy was within 85.6-103.2% and intra-day and inter-day precision did not exceed 12.1%. Perampanel was stable in samples collected by VAMS and stored under different storage conditions. The VAMS-LC-MS/MS method was validated according to internationally accepted criteria and tested in patients with epilepsy who were receiving a combination of perampanel and other antiseizure medications. The method showed adequate bioanalytical performances, holding great potential as an alternative strategy to support domiciliary TDM in patients with epilepsy treated with perampanel according to the simplicity of sample collection.

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.

New Trend in Toxicological Screening Using Volumetric Absorptive Microsampling (VAMS) and High-Resolution Mass Spectrometry (HR/MS) Combination

In toxicology, screenings are routinely performed using chromatographic methods coupled to detection systems such as high-resolution mass spectrometry (HR/MS). The increase in specificity and sensitivity of HRMS is responsible for the development of methods for alternative samples such as Volumetric Adsorptive Micro-Sampling. Whole blood overloaded with 90 drugs was sampled with 20 µL Mitra^TM to optimize the pre-analytical step as well as to determine the identification limits of drugs. Elution of chemicals was carried out in a solvent mixture through agitation and sonication. After dissolution, 10 μL was injected into the chromatographic system coupled to the Orbitrap^TM HR/MS. Compounds were confirmed against the laboratory library. The clinical feasibility was assessed in fifteen poisoned patients using the simultaneous sampling of plasma, whole blood and Mitra^TM. The optimized extraction procedure allowed us to confirm 87 compounds out of the 90 present in the spiked whole blood. Cannabis derivatives were not detected. For 82.2% of the investigated drugs, the identification limits were below 12.5 ng·mL^-1, with the extraction yields ranging from 80.6 to 108.7%. Regarding the patients' analysis, 98% of the compounds in plasma were detected in Mitra^TM compared to whole blood, with a satisfying concordance (R² = 0.827). Our novel screening approach opens new insights into different toxicologic fields appropriate for pediatrics, forensics or to perform mass screening.

Volumetric Absorptive Microsampling for the Therapeutic Drug Monitoring of Everolimus in Patients Who Have Undergone Liver Transplant

BACKGROUND

Therapeutic drug monitoring (TDM) of everolimus is required to prevent organ rejection in patients who have undergone transplant. Volumetric absorptive microsampling (VAMS) is a minimally invasive method for accurately collecting a small amount of blood from a patient's fingers. This study aimed to assess the applicability of VAMS for TDM of everolimus.

METHODS

VAMS and venous blood samples were collected from 45 liver transplant recipients who had been receiving stable everolimus doses for at least 7 days. Whole blood everolimus concentrations were measured using ultrahigh performance liquid chromatography with tandem mass spectrometry. Deming regression and Bland-Altman analysis were performed to compare everolimus concentrations measured using VAMS (C VAMS ) and venous blood samples (C IV ). The regression coefficient (r 2 ) between C VAMS and C IV was calculated using a linear regression. The effects of the hematocrit and blood sampling time on the difference between C VAMS and C IV were investigated.

RESULTS

Thirty-two participants were included in the final analysis. The Deming regression line was C IV = 1.04 × C VAMS + 0.55 [95% confidence interval (CI) of slope, 0.91-1.18; 95% CI of intercept, -0.05 to 1.16]. C VAMS and C IV were strongly correlated (r 2 = 0.92), with no proportional or constant bias. The mean difference between C VAMS and C IV was -0.79 ng/mL, with the 95% limit of agreement ranging from -2.55 to 0.97 ng/mL in a Bland-Altman plot. No effect of the hematocrit or blood sampling time was observed.

CONCLUSIONS

VAMS and venous blood sampling showed good agreement for the measurement of whole blood everolimus concentrations. Less invasive VAMS can substitute for more invasive venous blood sampling in the TDM of everolimus in liver transplant patients.

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.

Use of Antibiotics in Preterm Newborns

Due to complex maturational and physiological changes that characterize neonates and affect their response to pharmacological treatments, neonatal pharmacology is different from children and adults and deserves particular attention. Although preterms are usually considered part of the neonatal population, they have physiological and pharmacological hallmarks different from full-terms and, therefore, need specific considerations. Antibiotics are widely used among preterms. In fact, during their stay in neonatal intensive care units (NICUs), invasive procedures, including central catheters for parental nutrition and ventilators for respiratory support, are often sources of microbes and require antimicrobial treatments. Unfortunately, the majority of drugs administered to neonates are off-label due to the lack of clinical studies conducted on this special population. In fact, physiological and ethical concerns represent a huge limit in performing pharmacokinetic (PK) studies on these subjects, since they limit the number and volume of blood sampling. Therapeutic drug monitoring (TDM) is a useful tool that allows dose adjustments aiming to fit plasma concentrations within the therapeutic range and to reach specific drug target attainment. In this review of the last ten years’ literature, we performed Pubmed research aiming to summarize the PK aspects for the most used antibiotics in preterms.

Toward Therapeutic Drug Monitoring of Lenalidomide in Hematological Malignancy? Results of an Observational Study of the Exposure-Safety Relationship

Objective: Continuous lenalidomide (LEN) therapy is important to achieve a therapeutic effect in patients with multiple myeloma (MM) and non-Hodgkin lymphoma (NHL). However, despite dose adjustment according to kidney function, many patients discontinue LEN therapy because of hematological toxicity. To date, therapeutic drug monitoring (TDM) of LEN has not been performed in oncology, and no target concentration level has been yet defined. The aim of this study was to evaluate the exposure-safety relationship of LEN and determine the target concentration for toxicity.

Materials and Methods: A prospective observational study was designed and implemented. Blood samples were collected at 0.5 h (trough concentration, C_min) before oral administration and 1 h (C_1h) thereafter on the day. Clinical data were gathered from patients’ medical records and laboratory reports. Outcome measures of hematological toxicity were defined by the Common Terminology Criteria for Adverse Events. The concentration values were dichotomized by receiver operating characteristic (ROC) curve analysis, and the association between exposure and outcome was determined using the logistic regression model.

Results: Out of the 61 patients enrolled in this study, 40 (65.57%) had MM, and 21 (34.43%) had NHL. Hematological toxicity was reported in 15 (24.59%) patients. The LEN C_min showed remarkable differences (p = 0.031) among patients with or without hematological toxicity, while no association between C_1h values and toxicity was noted (p>0.05). By ROC analysis, a C_min threshold of 10.95 ng/mL was associated with the best sensitivity/specificity for toxicity events (AUC = 0.687; sensitivity = 0.40; specificity = 0.935). By multivariate logistic regression, an LEN C_min below 10.95 ng/mL was associated with a markedly decreased risk of hematological toxicity (<10.95 ng/mL vs. >10.95 ng/mL: OR = 0.023, 95% CI = 0.002–0.269; p = 0.003).

Conclusions: We demonstrate that the LEN trough concentration correlates with hematological toxicity, and the C_min threshold for hematological toxicity (10.95 ng/mL) is proposed. Altogether, LEN TDM appears to be a new approach to improve medication safety and achieve continuous treatment for patients with NHL or MM in routine clinical care.

Dried Volumetric Microsampling Approaches for the Therapeutic Drug Monitoring of Psychiatric Patients Undergoing Clozapine Treatment

Clozapine is one of the most widely used second-generation antipsychotic drugs (SGAs) for the treatment of schizophrenia. Despite advantages over first-generation drugs, clozapine still shows significant side effects and interindividual variations in efficacy. In order to ensure frequent therapeutic drug monitoring (TDM) and improve the compliance of psychiatric patients undergoing clozapine treatment, two novel dried microsampling approaches based on whole blood and plasma volumetric absorptive microsampling (b-VAMS and p-VAMS) and microfluidic generated-dried blood spot technology (mfDBS) were developed and coupled to HPLC with electrochemical detection (ED). The proposed miniaturized strategies by means of VAMS and microfluidic channel-based devices provide several advantages in terms of collection, storage, and handling compared to classical blood and plasma processing. Satisfactory validation results were obtained for all microsampling platforms, with mean extraction yields >85.1%, precision as relative standard deviation (RSD) < 5.1%, and stability < 4.5% analyte loss after 30 days for p-VAMS; mean extraction yields > 83.4%, precision RSD < 5.4%, and stability < 4.6% analyte loss after 30 days for b-VAMS, and mean extraction yields > 74.0%, precision RSD < 5.6%, and stability < 4.9% analyte loss after 30 days for mfDBS. The original microsampling methodologies have been successfully applied to the blood and plasma collected from five psychiatric patients for the monitoring of the levels of clozapine and its main metabolites, providing robust and reliable quali-quantitative results. Comparisons between results of the two dried microsampling technologies with those obtained by classic fluid plasma analysis were in good agreement and have demonstrated that the proposed miniaturized approaches could be suitable for TDM purposes.

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.

Use of TLC-Densitometric Method for Determination of Valproic Acid in Capsules

Determination of valproic acid in the drug was carried out on the aluminum silica gel 60F₂₅₄ plates and using acetone-water-chloroform-ethanol-ammonia at a volume ratio of 30:1:8:5:11 as the mobile phase, respectively. Two methods of detection of valproic acid were used. The first was a 2% aqueous CuSO₄×5H₂O solution, and the second was a 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system. The applied TLC-densitometric method is selective, linear, accurate, precise, and robust, regardless of the visualizing reagent used for the determination of valproic acid in Convulex capsules. It has low limits of detection (LOD) and limits of quantification (LOQ), which are equal to 5.8 μg/spot and 17.4 μg/spot using a 2% aqueous CuSO₄×5H₂O solution as visualizing agent and also 0.32 μg/spot and 0.97 μg/spot using a 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system as visualizing reagent, respectively. The described analytical method can additionally be used to study the identity of valproic acid in a pharmaceutical preparation. The linearity range was found to be 20.00-80.00 μg/spot and 1.00-2.00 μg/spot for valproic acid detected on chromatographic plates using a 2% aqueous CuSO₄×5H₂O solution and the 2',7'-dichlorofluorescein-aluminum chloride-iron (III) chloride system, respectively. A coefficient of variation that was less than 3% confirms the satisfactory accuracy and precision of the proposed method. The results of the assay of valproic acid equal 96.2% and 97.0% in relation to the label claim that valproic acid fulfill pharmacopoeial requirements. The developed TLC-densitometric method can be suitable for the routine analysis of valproic acid in pharmaceutical formulations. The proposed TLC-densitometry may be an alternative method to the modern high-performance liquid chromatography and square wave voltammetry in the control of above-mentioned substances, and it can be applied when other analytical techniques is not affordable in the laboratory.

Developing a Nationwide Infrastructure for Therapeutic Drug Monitoring of Targeted Oral Anticancer Drugs: The ON-TARGET Study Protocol

Simple Summary

Relationships between drug concentrations in blood and efficacy and/or toxicity have been reported for up to 80% of oral anticancer drugs (OADs). Most OADs exhibit highly variable drug concentrations at the approved dose. This may result in a significant proportion of patients with suboptimal drug concentrations. Therapeutic Drug Monitoring (TDM), which is dose optimization based on measured drug concentrations, can be used to personalize drug dosing with the overall goal to improve the benefit-risk ratio of anticancer drug treatment. The ON-TARGET study aims to investigate the feasibility of TDM in patients receiving either axitinib or cabozantinib for the treatment of renal-cell carcinoma with the main objective to improve severe tyrosine kinase inhibitor associated toxicity. Additionally, the feasibility of volumetric absorptive microsampling (VAMS), a novel minimally invasive and easy to handle blood sampling technique, for TDM sample collection is investigated.

Abstract

Exposure-efficacy and/or exposure-toxicity relationships have been identified for up to 80% of oral anticancer drugs (OADs). Usually, OADs are administered at fixed doses despite their high interindividual pharmacokinetic variability resulting in large differences in drug exposure. Consequently, a substantial proportion of patients receive a suboptimal dose. Therapeutic Drug Monitoring (TDM), i.e., dosing based on measured drug concentrations, may be used to improve treatment outcomes. The prospective, multicenter, non-interventional ON-TARGET study (DRKS00025325) aims to investigate the potential of routine TDM to reduce adverse drug reactions in renal cell carcinoma patients receiving axitinib or cabozantinib. Furthermore, the feasibility of using volumetric absorptive microsampling (VAMS), a minimally invasive and easy to handle blood sampling technique, for sample collection is examined. During routine visits, blood samples are collected and sent to bioanalytical laboratories. Venous and VAMS blood samples are collected in the first study phase to facilitate home-based capillary blood sampling in the second study phase. Within one week, the drug plasma concentrations are measured, interpreted, and reported back to the physician. Patients report their drug intake and toxicity using PRO-CTCAE-based questionnaires in dedicated diaries. Ultimately, the ON-TARGET study aims to develop a nationwide infrastructure for TDM for oral anticancer drugs.

Determination of Free Valproic Acid Concentration in 569 Clinical Samples by LC-MS/MS After Hollow Fiber Centrifugal Ultrafiltration Treatment

OBJECTIVE

To perform therapeutic drug monitoring of total and free plasma valproic acid (VPA) concentrations in clinical samples and to analyze the related factors.

METHODS

The total VPA concentration in plasma was determined by ultrahigh-performance liquid chromatography with precolumn derivatization with α-bromoacetophenone, and the free VPA concentration was determined by liquid chromatography-tandem mass spectrometry after the plasma was treated by hollow fiber centrifugal ultrafiltration. Regression analysis was performed to examine the associations between free plasma VPA, total plasma VPA, and the plasma protein binding rate. The impact of individual situations, outpatient or inpatient factors, and drug combinations on VPA concentrations were examined.

RESULTS

Of the 569 clinical samples, 268 were inpatients and 301 were outpatients, and the total VPA concentration in 138 cases (24.2%) was lower than the effective treatment concentration range; the total and free VPA concentrations in outpatient samples were 11.0% and 26.1% higher than those of inpatients, respectively. There was no linear relationship between the free and total VPA concentrations. The relationship equation between the plasma protein binding rate and free VPA concentrations was as follows: Y = 0.0255X2 - 1.1357X + 97.429 (r = 0.8011). The total and free VPA concentrations were significantly decreased after the coadministration of phenobarbital (83.7% and 64.3% of the control group, P < 0.05) or carbapenem antibiotics (32.0% and 32.7% of the control group, P < 0.05).

CONCLUSIONS

The total VPA concentrations in patients with epilepsy at our hospital was lower than the effective treatment concentration range, which was inadequate for epilepsy control; the total VPA concentrations of outpatients were higher than those of inpatients; as phenobarbital affects VPA metabolism, therapeutic drug monitoring is recommended. Carbapenem antibiotic coadministration with VPA should be avoided because carbapenem antibiotics can lead to the failure of VPA antiepileptic treatment.

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.

Validation of LC-MS/MS method for determination of rosuvastatin concentration in human blood collected by volumetric absorptive microsampling (VAMS)

In light of the shift toward patient-centric clinical trials, a measure of simplifying blood collection process and minimizing the volume of blood samples is on the rise. Volumetric absorptive microsampling (VAMS) is a microsampling device developed for blood sampling in non-hospital settings, which enables accurate hematocrit-independent collection of 10 or 20 µL of whole blood with a simple finger prick. In this study, liquid chromatography (LC)-tandem mass spectrometry workflow for quantification of rosuvastatin after VAMS sampling was developed and validated. The VAMS sample was stabilized by matrix drying and the optimum LC conditions and extraction methods were used to reach adequate sensitivity with lower limit of quantification verified at 1 ng/mL in 10 µL of blood. The bioanalytical method to quantify rosuvastatin from 1 to 100 ng/mL in VAMS sample was qualified by specificity, carryover, linearity, within-run and between-run reproducibility and stability. Inaccuracy was less than ± 6% and imprecision was less than 10% after analyzing the samples on 5 different days at all concentration levels. In addition, the feasibility of delivery to the analytical laboratory after home sampling during the guaranteed stability period of 10 days at room temperature was confirmed by evaluating concentration changes after VAMS sampling without adding pH buffer. Our results suggest that VAMS sampling did not have an effect on the stability of rosuvastatin, and it is a viable option for simple and accurate blood collection at home.

Multiplex Analysis of 230 Medications and 30 Illicit Compounds in Dried Blood Spots and Urine

Drugs of abuse and medication reconciliation testing can benefit from analysis methods capable of detecting a broader range of drug classes and analytes. Mass spectrometry analysis of a wide variety of commonly prescribed medications and over-the-counter drugs per sample also allows for application of a drug-drug interaction (DDI) algorithm to detect adverse drug reactions. In order to prevent adulteration of commonly collected clinical samples such as urine, dried blood spots (DBS) present a reliable alternative. A novel method is described for qualitative and quantitative multiplex analysis of 230 parent drugs, 30 illicit drugs and 43 confirmatory metabolites by HPLC-MS-MS This method is applicable to DBS specimens collected by volumetric absorptive microsamplers and confirmable in urine specimens. A patient cohort (n = 67) providing simultaneous urine specimens and DBS resulted in 100% positive predictive values of medications or illicits confirmed by detection of a parent drug and/or its metabolite during routine medication adherence analysis. An additional 5,508 DBS specimens screened (n = 5,575) showed 5,428 (97%) with an inconsistent positive compared to the provided medication list (including caffeine, cotinine or ethanol metabolites), 29 (0.5%) with no medication list and no unexpected positive results (consistent negative) and 22 (0.4%) showed all positive results matching the provided medication list (consistent positive). A DDI algorithm applied to all positive results revealed 17% with serious and 56% with moderate DDI warnings. Comprehensive DBS analysis proves a reliable alternative to urine drug testing for extended medication reconciliation, with the added advantage of detecting DDIs.

Therapeutic Drug Monitoring of Antiseizure Medications Using Volumetric Absorptive Microsampling: Where Are We?

Therapeutic drug monitoring (TDM) of antiseizure medications (ASMs) represents a valuable tool to establish an appropriate patient therapy, to collect important information about drugs’ interactions and to evaluate patient’s metabolic capabilities. In recent years, a new volumetric absorptive microsampling technique using VAMS^® technology and Mitra^® devices, consisting of a sampling technique for the collection of fixed-volume capillary blood, was developed. These new devices provide a new home-sampling technique for whole blood that has been spread out to simplify sample collection from finger-pricks. This review is aimed to compare published articles concerning the application of VAMS^® in epilepsy and to identify the strengths and improvement points for the TDM of antiseizure medications. VAMS^® allowed a minimally invasive blood sampling even in the absence of trained personnel. Good stability data have indicated that storage and delivery can be facilitated only for specific ASMs. Trueness and precision parameters have been evaluated, and the hematocrit (HCT) effect was minimized.

Microsampling: A role to play in Covid-19 diagnosis, surveillance, treatment and clinical trials

The outbreak of the new coronavirus disease changed the world upside down. Every day, millions of people were subjected to diagnostic testing for Covid-19, all over the world. Molecular tests helped in the diagnosis of current infection by detecting the presence of viral genome whereas serological tests helped in detecting the presence of antibody in blood as well as contributed to vaccine development. This testing helped in understanding the immunogenicity, community prevalence, geographical spread and conditions post-infection. However, with the contagious nature of the virus, biological specimen sampling involved the risk of transmission and spread of infection. Clinic or pathology visit was the most concerning part. Trained personnel and resources was another barrier. In this scenario, microsampling played an important role due to its most important advantage of remote, contactless, small volume and self-sampling. Minimum requirements for sample storage and ease of shipment added value in this situation. The highly sensitive instruments and validated assay formats assured the accuracy of results and stability of samples. Microsampling techniques are contributing effectively to the Covid-19 pandemic by reducing the demand for clinical staff in population-level testing. The validated and established applications supported the use of microsampling in diagnosis, therapeutic drug monitoring, development of treatment or vaccines and clinical trials for Covid-19.

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.

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.

Therapeutic Drug Monitoring of Lamotrigine, Lacosamide, and Levetiracetam in Dried Capillary Blood-Determination of Conversion Factors for Serum-Based Reference Ranges

BACKGROUND

Drug concentrations of antiepileptic drugs (AEDs) are routinely determined from blood serum or plasma at trough levels (before intake of morning dose). In capillary blood collection, blood is taken from the fingertip with the aid of a disposable tool and dried on absorbent material. The volumetric absorptive microsampling technique offers several advantages over the use of filter paper cards. The aim of this study was to determine conversion factors for the estimation of AED serum concentrations from capillary blood concentrations.

METHODS

Venous and capillary blood samples were collected from adult inpatients with epilepsy who were treated with lacosamide (LCM, n = 30), lamotrigine (LTG, n = 40), and/or levetiracetam (LEV, n = 36). A validated liquid chromatography-mass spectrometry (LC-MS) method for dried blood samples for these AEDs was compared with routine serum laboratory methods. Method agreement was evaluated using different regression techniques, and the conversion factors were calculated.

RESULTS

Regression analyses revealed a linear relationship between serum and capillary blood concentrations for all 3 AEDs (r ≥ 0.95). For LTG, the regression intercept was significantly different from 0, indicating that the relationship was linear, but not necessarily proportional. Although LEV and LCM concentrations tended to be lower in capillary blood than in serum (mean ratio of serum concentration to capillary blood concentration: 1.14 and 1.22, respectively), LTG concentrations were higher in capillary blood (mean ratio = 0.85).

CONCLUSIONS

The estimation of serum concentrations from measured capillary blood concentrations is feasible for LCM, LTG, and LEV. A simple ratio approach using the mean ratio and Passing-Bablok regression showed the best results for all 3 AEDs. The volumetric absorptive microsampling technique facilitates the quantitative sample collection of capillary blood and overcomes the drawbacks associated with the classical dried blood spot technique.

Volumetric Absorptive Microsampling as an Alternative Tool for Biomonitoring of Multi-Mycotoxin Exposure in Resource-Limited Areas

Biomonitoring of biological samples arises as an effective tool to evaluate the exposure to mycotoxins in the population. Owing to the wide range of advantages, there is a growing interest in the use of non- and minimally invasive alternative sampling strategies, such as dried blood spot sampling or volumetric absorptive microsampling (VAMS). A VAMS-based multi-mycotoxin method was developed and validated for 24 different mycotoxins. Method validation was based on the Bioanalytical Method Validation Guideline of the Food and Drug Administration from the United States and for most of the studied mycotoxins, the results of the performance characteristics were in agreement with the criteria of the European Commission Decision 2002/657/EC. The recovery for the different mycotoxins was not haematocrit dependent and remained acceptable after storing the VAMS for 7 and 21 days at refrigeration temperature (4 °C) and room temperature, demonstrating that VAMS could be applied to assess mycotoxin exposure in blood in resource-limited areas, where there may be a delay between sampling and analysis. Finally, a comparison between VAMS and a procedure for liquid whole blood analysis, performed on 20 different blood samples, did not result in missed exposed cases for VAMS. Moreover, both methods detected similar levels of ochratoxin A, ochratoxin alpha, zearalenone and aflatoxin B1. Given all the benefits associated with VAMS and the developed method, VAMS sampling may serve as an alternative to conventional venous sampling to evaluate multiple mycotoxin exposure.

Whole blood stability evaluation of monoclonal antibody therapeutics using volumetric absorptive microsampling

Volumetric absorptive microsampling (VAMS) is increasingly utilized for both nonclinical and clinical pharmacokinetic studies. Currently, VAMS is employed as the sampling method for the detection of antibodies for coronavirus disease 2019. Biotherapeutics whole blood stability on VAMS presents as a critical concern for the health and pharmaceutical industries. In this follow-up to our previous publication, we evaluated daclizumab and trastuzumab whole blood sample stability on VAMS. The drug recovery data we observed at room temperature for short term and -80°C for long term was very encouraging. The knowledge could help us better understand and plan important investigation timelines, especially pandemic situations where human whole blood samples from a large population are collected and in urgent need of data analysis.

Volumetric Absorptive Microsampling of Blood for Untargeted Lipidomics

In the present, proof-of-concept paper, we explore the potential of one common solid support for blood microsampling (dried blood spot, DBS) and a device (volumetric absorptive microsampling, VAMS) developed for the untargeted lipidomic profiling of human whole blood, performed by high-resolution LC-MS/MS. Dried blood microsamples obtained by means of DBS and VAMS were extracted with different solvent compositions and compared with fluid blood to evaluate their efficiency in profiling the lipid chemical space in the most broad way. Although more effort is needed to better characterize this approach, our results indicate that VAMS is a viable option for untargeted studies and its use will bring all the corresponding known advantages in the field of lipidomics, such as haematocrit independence.

A review of recent advances in microsampling techniques of biological fluids for therapeutic drug monitoring

Conventional sampling of biological fluids often involves a bulk quantity of samples that are tedious to collect, deliver and process. Miniaturized sampling approaches have emerged as promising tools for sample collection due to numerous advantages such as minute sample size, patient friendliness and ease of shipment. This article reviews the applications and advances of microsampling techniques in therapeutic drug monitoring (TDM), covering the period January 2015 - August 2020. As whole blood is the gold standard sampling matrix for TDM, this article comprehensively highlights the most historical microsampling technique, the dried blood spot (DBS), and its development. Advanced developments of DBS, ranging from various automation DBS, paper spray mass spectrometry (PS-MS), 3D dried blood spheroids and volumetric absorptive paper disc (VAPD) and mini-disc (VAPDmini) are discussed. The volumetric absorptive microsampling (VAMS) approach, which overcomes the hematocrit effect associated with the DBS sample, has been employed in recent TDM. The sample collection and sample preparation details in DBS and VAMS are outlined and summarized. This review also delineates the involvement of other biological fluids (plasma, urine, breast milk and saliva) and their miniaturized dried matrix forms in TDM. Specific features and challenges of each microsampling technique are identified and comparison studies are reviewed.

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.

New Methods Used in Pharmacokinetics and Therapeutic Monitoring of the First and Newer Generations of Antiepileptic Drugs (AEDs)

The review presents data from the last few years on bioanalytical methods used in therapeutic drug monitoring (TDM) of the 1st-3rd generation and the newest antiepileptic drug (AEDs) cenobamate in patients with various forms of seizures. Chemical classification, structure, mechanism of action, pharmacokinetic data and therapeutic ranges for total and free fractions and interactions were collected. The primary data on bioanalytical methods for AEDs determination included biological matrices, sample preparation, dried blood spot (DBS) analysis, column resolution, detection method, validation parameters, and clinical utility. In conclusion, the most frequently described method used in AED analysis is the LC-based technique (HPLC, UHPLC, USLC) combined with highly sensitive mass detection or fluorescence detection. However, less sensitive UV is also used. Capillary electrophoresis and gas chromatography have been rarely applied. Besides the precipitation of proteins or LLE, an automatic SPE is often a sample preparation method. Derivatization was also indicated to improve sensitivity and automate the analysis. The usefulness of the methods for TDM was also highlighted.

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^®.

Giving patients choices: AstraZeneca's evolving approach to patient-centric sampling

This paper shares experiences and learning from introducing patient-centric sampling (PCS) into AstraZeneca trials. Through two case studies we show how modeling approaches can assist pharmacokinetic (PK) bridging studies accounting for blood partitioning and hematocrit and how reduced PK sampling schedules, profiles constructed from composite data (plasma & dry blood) and combined assays (PK & pharmacodynamic) can all reduce patient sampling burden without impacting study outcomes. Following sharing some clinical operational challenges, we finally highlight some key requirements for implementing a patient-centric sampling strategy such as collaborative working across organizational silos, continuous patient engagement throughout the study life cycle and accepting that if the aim is to give patient choice, then one solution (device, procedure and design) will not fit all.

Therapeutic drug monitoring of anti-epileptic drugs – a clinical verification of volumetric absorptive micro sampling

Background

Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) can serve as a valuable tool in optimising and individualising epilepsy treatment, especially in vulnerable groups such as pregnant women, the elderly and children. Unfortunately, TDM is often performed suboptimally due to limitations in blood collection. Therefore, we investigated volumetric absorptive micro sampling (VAMS) – a new home-sampling technique. We aimed to evaluate VAMS to determine and quantify the different AEDs and concentrations of 16 different AEDs in whole blood collected by VAMS.

Methods

Patient blood samples (n = 138) were collected via venepunctures at the Academic Centre for Epileptology Kempenhaeghe. AED concentrations were determined, and these concentrations were used to compare the VAMS method (whole blood) with the conventional method (serum). In addition, the recovery was examined as well as the impact of haematocrit. Finally, AED-spiked blood was used to test the stability of the AEDs inside the micro-sampler devices over a period of time and whether temperature had an effect on the stability.

Results

VAMS allows for an accurate detection of 16 different AEDs within 2 days after sampling. Deviation in recovery was less than 10% and high correlations were found between VAMS and conventional sampling. Moreover, haematocrit does not have an effect with values between 0.3 and 0.5 (L/L). Finally, although storage temperature of VAMS does affect some AEDs, most are unaffected.

Conclusions

VAMS enables an accurate detection of a wide variety of AEDs within 2 days after sampling.

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.

Transition of Methotrexate Polyglutamate Drug Monitoring Assay from Venipuncture to Capillary Blood-Based Collection Method in Rheumatic Diseases

Objective

Methotrexate (MTX) polyglutamate (MTXPG3) levels from isolated red blood cells (RBCs) collected by venipuncture have clinical utility in guiding MTX dosing for patients with rheumatoid arthritis (RA). Our objective was to transition this RBC-based therapeutic drug monitoring (TDM) assay to dried capillary blood collected by fingerstick.

Methods

Patients with RA treated with MTX were enrolled. Specimens were collected by fingerstick (volumetric absorptive microsampler) and venipuncture to measure MTXPG3 from dried capillary blood, total venous blood, and isolated RBCs. MTXPG3 levels from dried capillary blood were measured using LC-MS/MS, converted to RBC equivalent (nmol/L), and compared with those from isolated RBCs (reference method). Following transition to fingerstick collection, comparability in the distributions of dried capillary and venipuncture-based RBC MTXPG3 levels was assessed using the Kolmogorov–Smirnov (K-S) test.

Results

Intraday and interday precision ranged from 2.0% to 10.9% and 3.1% to 10.8%, respectively, at MTXPG3 concentrations ranging from 5 to 100 nmol/L. In 106 participants treated with MTX, MTXPG3 levels from total venous and dried capillary blood were comparable [slope = 0.97 (95% CI, 0.92–1.03); R2 = 0.92]. Dried capillary blood MTXPG3 converted to RBC equivalent was similar to levels from isolated RBCs (30 ± 18 nmol/L vs 33 ± 19 nmol/L; n = 106). After implementation in the clinical laboratory, RBC equivalents MTXPG3 from the fingerstick method were similar to levels from venipuncture [39 ± 22 nmol/L (n = 825) vs 39 ± 24 nmol/L (n = 47935)] (K-S test P = 0.09). Underexposure to MTX (MTXPG3 ≤5 nmol/L RBCs) was detected in 7.0% and 8.5% patient specimens collected using the fingerstick and venipuncture methods, respectively.

Conclusion

Capillary blood MTXPG3 levels can be used to guide MTX dosing in TDM 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.