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

Determination by UHPLC-QTOF-HRMS of Phosphatidylethanol (PEth) in Dried Blood Spots: Method Validation and Practical Application of a Rising Alcohol Abuse Biomarker With Minimally Invasive Sampling

The goal of our study was to develop and validate a simple, quick, and sensitive method to detect phosphatidylethanol (PEth) in dried blood spots (DBS). A 30-μL aliquot of blood was collected on a DBS card and allowed to dry at room temperature. Then, the spot was cut and transferred into a clean tube where the internal standard (PEth-D5) and 1-mL hexane were added followed by stirring, sonication, and centrifugation at room temperature. The dried supernatant was reconstituted with 30-μL acetonitrile and analyzed by UHPLC-HRMS-QTOF. Calibration curve was created at 20, 50, 100, 200, 300, and 500 ng/mL; the limit of detection was calculated at 5 ng/mL (S/N > 3) while accuracy, precision, recovery, and matrix effect were successfully evaluated, along with the analyte stability at different time intervals and temperatures. The study demonstrates that quantifying PEth 16:0/18:1 from DBS cards is feasible using UHPLC-QTOF or UHPLC-QqQ instrumentation while the QTOF method was validated and proved reliable for PEth detection to assess both excessive alcohol consumption and alcohol abstinence, matching current guidelines. Preliminary data on authentic samples confirmed the method's performance in terms of ease, sustainability, and speed, supporting its great potential for routine toxicological diagnosis of chronic alcohol abuse.

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.

The Use of Surrogate Matrix for Calibrators in the Analysis of Dried Blood Samples - A Feasibility Study

Experiments designed to assess the ability to analyze Volumetric Absorptive Microsampling (VAMS®) or Tasso-M20 dried blood samples using ligand binding assays to support pharmacokinetic studies are described. An internally developed monoclonal antibody therapeutic A (mAb A) was employed as a model compound to facilitate this evaluation. The challenges of daily preparation of VAMS® calibrators in wet blood and the identification of a suitable diluent for use with dried blood samples at high analyte concentrations were addressed. A suitable surrogate matrix solution was identified for constructing calibrators, enabling accurate quantitation from dried blood samples. Additionally, utilizing surrogate matrix solutions as a diluent confirmed the absence of bias in the quantitation of diluted samples. The results of this feasibility study demonstrate the potential of using a surrogate matrix solution to address challenges associated with the analysis of dried blood samples via ligand binding methodology.

Volumetric absorptive microsampling to measure iohexol and creatinine concentrations for estimation of glomerular filtration rate in cats: aligning animal welfare with practical feasibility

BACKGROUND

Chronic kidney disease (CKD) is common in cats, and early detection is crucial for better prognosis. Currently, the gold standard to assess renal function is the measurement of glomerular filtration rate (GFR), allowing early detection of decreased kidney function. To overcome the practical limitations of this procedure, microsampling, collecting a small drop of blood from the cat's ear, can be used. Application of volumetric absorptive microsampling (VAMS) in feline nephrology would be of tremendous value, aligning with animal welfare and improving practical feasibility of GFR measurements.

RESULTS

We developed and successfully validated liquid chromatography - tandem mass spectrometry (LC-MS/MS) methods to simultaneously determine iohexol and creatinine in plasma, blood and VAMS samples. A clinical validation study, conducted in 23 cats from whom conventional venous blood, plasma and VAMS samples were collected, allowed to establish a conversion formula to derive plasma iohexol or creatinine concentrations from capillary VAMS concentrations. This conversion was applied on an independent set, revealing an excellent agreement for both iohexol and creatinine between concentrations directly measured in venous plasma or derived from ear-prick VAMS samples (94% and 96% of differences lay < 20%, respectively).

CONCLUSIONS

We demonstrated that ear-prick sampling using VAMS is a suitable alternative to conventional venous sampling to measure iohexol and creatinine for GFR determination in cats.

A validated method for capillary phosphatidylethanol 16:0/18:1 quantification with two different 10-µl volumetric absorptive microsample devices in the same setup

There is a growing interest for quantification of drugs in capillary blood. Phosphatidylethanol (PEth) is a biomarker for alcohol intake measured in whole blood, thus making it a candidate for capillary sampling. Our laboratory has been running a method for PEth quantification in venous blood since 2016, and we aimed to expand this method to also include capillary dried blood spot (DBS) samples. Two 10-µl volumetric absorptive microsampling (VAMS) devices, Capitainer®B Vanadate and Mitra®, were included in the method development and validated. Calibrators and quality controls were spiked during automatic sample extraction without the VAMS devices present, making it possible to extract and analyze both types of VAMS samples in the same setup. With the Mitra device, all pre-established validation criteria were fulfilled in the measuring range of 0.03 to 4.0 µM (21-2812 ng/mL), including method comparison with our venous blood method. Capitainer fulfilled all validation criteria, except for the accuracy of samples with PEth levels ≥ 0.5 µM (≥ 352 ng/mL) (deviation -17.1% to -20.5%). The correlation analysis between Capitainer and the venous blood results showed no constant bias, but an acceptable small proportional mean difference of -7.6%. Overall, the method validation results for both Capitainer and Mitra were considered acceptable. Both devices were found to be suitable for the analyses of PEth.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Clinical validation of an innovative dried whole-blood spot method to quantify simultaneously vancomycin and creatinine in adult patients

BACKGROUND

A drawback of vancomycin use is the need for therapeutic drug monitoring and renal function monitoring. Traditional blood sampling involves drawing blood through a venepuncture. An alternative method, dried blood spot (DBS) sampling allows for self-sampling at home.

OBJECTIVES

To clinically validate a DBS method for simultaneous monitoring of vancomycin and creatinine.

METHODS

Hospitalized adults treated with intravenous vancomycin were included (trial registration NCT05257070). Blood sampling consisted of one venepuncture and one finger prick. Whole-blood DBS samples from patients were obtained by applying one drop of whole blood onto Whatman 903 filtrate paper. Bland-Altman analyses were used to assess the agreement and bias between the two measurements. Patients were asked to state their preferences for one of the two sampling methods.

RESULTS

The study involved a final analysis of 39 patient samples for the clinical validation of vancomycin and 46 patient samples for the clinical validation of creatinine. The difference between plasma and DBS concentrations was ≤20% for 77% of the vancomycin samples, the mean bias was -0.1379% (95% limit of agreement -5.899-5.623). The difference between plasma and DBS concentrations was ≤20% for 89% of the creatinine samples, the mean bias was 2.656% (95% limit of agreement -26.16-31.47). Most patients (18 out of 31) preferred a finger prick over a venepuncture and 12 patients indicated no preference.

CONCLUSIONS

This is the first study that successfully clinically validated a DBS sampling method for simultaneous measurement of vancomycin and creatinine, allowing for direct use in (outpatient) practice.

Imatinib and norimatinib therapeutic monitoring using dried blood spots: Analytical and clinical validation, and performance comparison of volumetric collection devices

Therapeutic drug monitoring during imatinib treatment is recommended to optimize patient clinical outcomes. This study aimed to develop a novel LC-MS/MS method to quantitate imatinib and its active metabolite N-desmethyl-imatinib, in volumetric dried blood spots (DBS) using the HemaXis DB10 and Capitainer B devices. Chromatographic separation was achieved using an XTerra MS C18 column and detection occurred with a SCIEX 4000QTrap tandem mass spectrometer using electrospray positive-mode ionization. Analytical validation was successfully performed adhering to the latest guidelines. The assay was linear over the range 240-6000 ng/mL for imatinib and 48-1200 ng/mL for its metabolite, accurate (89 %-113 %) and precise (≤17 % imprecision) across a hematocrit range of 22-55 % for both devices. Recovery ranged from 84 % to 92 %, with no influence of matrix components. Stability was confirmed after at least 43 days in desiccator conditions (20 °C, ≤35 % humidity), and in conditions that mimed home-sampling. Clinical validation, conducted on 52 paired DBS and plasma samples from 28 patients, revealed that the DBS-to-plasma ratio can be used to convert DBS measurements into plasma concentrations. Bland-Altman and Passing-Bablok analyses indicated strong agreement between the estimated and actual plasma concentrations for both imatinib and its metabolite across both devices. The conversion method was further tested on an additional set of 25 to 31 samples, with 80 to 97 % of the samples falling within ±20 % difference. This study proved that DBS collected using either HemaXis DB10 or Capitainer B devices can be reliably implemented as an alternative to plasma for therapeutic drug monitoring during imatinib therapy.

Dried blood spot LC-MS/MS quantification of voclosporin in renal transplant recipients using volumetric dried blood spot sampling

Voclosporin is a potent immunosuppressive agent currently approved for treating active lupus nephritis. Based on its potential antiviral activity, it has also been investigated as immunosuppressive agent in an investigator-initiated study in SARS-CoV2 positive kidney transplant recipients. As with many immunosuppressive agents, optimizing dosing regimens to achieve therapeutic efficacy while minimizing toxicity remains a critical challenge in clinical practice. To prevent organ rejection as well as infections, the prescribed immunosuppression needs to be well balanced. Dried blood spot (DBS) sampling has enabled development of remote voclosporin therapeutic drug monitoring. Here, we report on the development and analytical validation of a liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for quantification of voclosporin in dried blood spots. Method development was based on previously developed assays for the quantification of tacrolimus, everolimus, sirolimus, cyclosporin, mycophenolic acid, creatinine and iohexol in DBS and voclosporin in whole blood using LC-MS/MS. HemaXis™ volumetric blood spot devices were used for sample collection. The sample purification was based on the extraction of voclosporin from the DBS samples. Stable isotopically labeled voclosporin-D4 was used as an internal standard prior to sample purification. Bland Altman and Passing bablok analysis were performed for cross validation between whole blood and DBS samples. The method was successfully validated following the current ICH M10 guidelines. The dynamic range for the analyte was 10-600 µg/L with an excellent mean coefficient of correlation of 0.9978. The within run and between run precision and accuracy were both within the acceptance criteria. The cross-validation against the whole blood method shows that the quantified voclosporin results are promising. This developed dried blood spot LC-MS/MS method was successfully validated and provides an easy, efficient workflow for therapeutic drug monitoring in kidney transplant patients or remote pharmacokinetic studies in lupus nephritis patients treated with voclosporin.

Therapeutic drug monitoring of levetiracetam - Is dried blood spot sampling suitable?

BACKGROUND

Therapeutic drug monitoring helps prevent seizures and minimize side effects in epilepsy patients. Phlebotomy is the gold standard for blood collection but can be difficult for children, pregnant women, and patients in remote areas. We previously validated dried blood spot (DBS) sampling for carbamazepine, lamotrigine, levetiracetam (LEV), and valproic acid. Uncertainties in LEV comparisons from the previous validation were further investigated in this study by increasing sample numbers and comparing results using both immunochemistry and LC-MS/MS methods. Additionally, capillary and venous DBS were compared, and the stability of samples during mail transport was assessed.

AIM

To compare LEV concentrations in capillary DBS and plasma, and to assess the stability of capillary DBS during transportation.

METHOD

Capillary and venous blood samples were collected from 40 LEV-treated patients. Concentrations were measured using immunochemistry and liquid chromatography tandem mass spectrometry methods. Comparisons between matrices and methods were analyzed with Passing-Bablok regression and Bland-Altman plots.

RESULTS

No proportional bias was found in regression analysis and Bland-Altman plots showed no bias between methods. For capillary DBS versus plasma concentrations, 92.1 % of values were within 20 % of the mean. No bias was detected between capillary and venous DBS, with deviations within acceptable limits. Sample stability was maintained during mail transport.

CONCLUSION

The concentrations obtained for LEV in capillary DBS versus plasma showed that therapeutic drug monitoring of LEV can be performed as at-home self-sampling with DBS mailed to the laboratory for analysis.

Analytical and clinical validation of a volumetric absorptive microsampling (VAMS) - Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for the analysis of Clofazimine in whole blood

Monitoring clofazimine blood concentrations is crucial for preventing treatment failure in patients with Multidrug-resistant Tuberculosis (MDR-TB). Volumetric Absorptive Microsampling (VAMS) offers a practical alternative to Conventional Venous Sampling (CVS), enabling remote sampling. Samples collected via VAMS can be conveniently transported to laboratories via courier, enhancing accessibility and patient compliance. In this study, we developed and validated an analytical method for quantifying clofazimine in whole blood collected using VAMS. The study compared the performance and cost-effectiveness of VAMS with CVS. A total of 55 matched finger-prick VAMS and CVS samples were obtained from 39 MDR-TB patients and analyzed using validated UPLC-MS/MS assays. Clofazimine concentrations collected via VAMS and CVS were compared using Passing-Bablok regression, while bias and overall agreement were evaluated through Bland-Altman analysis. Passing-Bablok regression revealed no significant constant difference between VAMS and CVS (95% CI slope: 0.7627-0.9573; 95% CI intercept: -0.02141-0.06482), but systematic difference of 13% lower clofazimine concentrations was observed in VAMS compared to plasma. Bland-Altman analysis demonstrated moderate agreement, with mean plasma/VAMS ratio of 0.9457 (95% CI: 0.88358-1.00775) and 95% Limits of Agreement (LoA) ranging from 0.4956 (95% CI: 0.38881-0.60230) to 1.3858 (95% CI: 1.28903-1.50252). Although statistically significant bias was identified, applying correction factors could improve interchangeability between the two techniques. Furthermore, VAMS was more cost-effective than CVS, with approximate cost difference of 4.45 USD per sample. These findings suggest that VAMS sampling has the potential to replace CVS for routine clinical monitoring of clofazimine, offering a more accessible and economical approach.

Microsampling techniques and patient-centric therapeutic drug monitoring of immunosuppressants

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

Clinical Application of Volumetric Absorptive Microsampling for Therapeutic Drug Monitoring of Oral Targeted Anticancer Drugs

BACKGROUND

Therapeutic Drug Monitoring optimizes oral anticancer drug treatment by measuring plasma levels. Volumetric absorptive microsampling (VAMS) allows home sampling with a minimal blood sample. However, methods for converting whole blood into plasma are required to interpret these results. This study aimed to establish conversion methods for abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and their metabolites, while assessing the differences between venous and capillary blood. The feasibility of home sampling was also evaluated.

METHODS

Plasma and VAMS samples, both from venipuncture-collected whole blood tubes and from a finger prick, were collected from each patient. The VAMS samples were deemed comparable if their concentrations were within ±20% of each other for ≥2/3rd of the patients. The Passing-Bablok regression and conversion factor methods were tested for the plasma and VAMS finger prick samples. The estimated plasma concentrations using both methods were required to be within ±20% of the measured plasma concentrations for ≥2/3rd of the pairs.

RESULTS

Overall, 153 patients were enrolled in this study. Conversion methods were applied to the VAMS samples, and the acceptance criteria were met for alectinib-M4, cabozantinib, imatinib, N-desmethyl imatinib, olaparib, sunitinib, and N-desethyl sunitinib but not for abiraterone, D4A, or alectinib. The capillary and venous VAMS concentrations were similar, except for that of D4A. Patients were positive toward home sampling.

CONCLUSIONS

The established VAMS conversion methods for 7 out of 10 oral targeted anticancer drugs or metabolites met the acceptance criteria. Future studies need to validate the conversion methods with an independent cohort and integrate home sampling via VAMS to provide patients with an alternative to venipuncture at the outpatient clinic.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Getting Tacrolimus Dosing Right

ABSTRACT

Tacrolimus (TAC) dosing is typically guided by the trough concentration (C0). Yet, significant relationships between TAC C0 and clinical outcomes have seldom been reported or only with adverse events. Large retrospective studies found a moderate correlation between TAC C0 and the area under the curve (AUC), where, for any given C0 value, the AUC varied 3- to 4-fold between patients (and vice versa). However, no randomized controlled trial evaluating the dose adjustment based on TAC AUC has been conducted yet. A few observational studies have shown that the AUC is associated with efficacy and, to a lesser extent, adverse effects. Other studies showed the feasibility of reaching predefined target ranges and reducing underexposure and overexposure. TAC AUC 0-12 h is now most often assessed using Bayesian estimation, but machine learning is a promising approach. Microsampling devices are well accepted by patients and represent a valuable alternative to venous blood sample collection during hospital visits, especially when a limited sampling strategy is required. As AUC monitoring cannot be proposed very frequently, C0 monitoring has to be used in the interim, which has led to fluctuating doses in patients with an AUC/C0 ratio far from the population mean, because of different dose recommendations between the 2 biomarkers. We proposed estimating the individual AUC/C0 ratio and derived individual C0 targets to be used in between or as a replacement for AUC monitoring. Existing technology and evidence are now sufficient to propose AUC monitoring interspersed with individualized-C0 monitoring for all patients with kidney transplants while collecting real-world data to strengthen the evidence.

Everolimus Personalized Therapy: Second Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

The Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology established the second consensus report to guide therapeutic drug monitoring (TDM) of everolimus (EVR) and its optimal use in clinical practice 7 years after the first version was published in 2016. This version provides information focused on new developments that have arisen in the last 7 years. For the general aspects of the pharmacology and TDM of EVR that have retained their relevance, readers can refer to the 2016 document. This edition includes new evidence from the literature, focusing on the topics updated during the last 7 years, including indirect pharmacological effects of EVR on the mammalian target of rapamycin complex 2 with the major mechanism of direct inhibition of the mammalian target of rapamycin complex 1. In addition, various concepts and technical options to monitor EVR concentrations, improve analytical performance, and increase the number of options available for immunochemical analytical methods have been included. Only limited new pharmacogenetic information regarding EVR has emerged; however, pharmacometrics and model-informed precision dosing have been constructed using physiological parameters as covariates, including pharmacogenetic information. In clinical settings, EVR is combined with a decreased dose of calcineurin inhibitors, such as tacrolimus and cyclosporine, instead of mycophenolic acid. The literature and recommendations for specific organ transplantations, such as that of the kidneys, liver, heart, and lungs, as well as for oncology and pediatrics have been updated. EVR TDM for pancreatic and islet transplantation has been added to this edition. The pharmacodynamic monitoring of EVR in organ transplantation has also been updated. These updates and additions, along with the previous version of this consensus document, will be helpful to clinicians and researchers treating patients receiving EVR.

Steroid hormone concentrations in dried blood spots: A comparison between capillary and venous blood samples

BACKGROUND

An important aspect of the shift towards dried blood spots (DBS) as a sample matrix for laboratory measurements, is the availability of robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods that can reliably quantify analyte concentrations in DBS. The development and validation of these LC-MS/MS methods, however, concerns an extensive process, for which large amounts of DBS samples are required. DBS are usually obtained from capillary blood samples, but they can also be prepared from venous (residual) blood samples, which are widely available in clinical laboratories. Therefore, we aimed to determine whether DBS prepared from (residual) venous blood samples, collected in EDTA blood tubes, can be used for future development and validation of LC-MS/MS methods to quantify steroid hormones in DBS.

METHODS

Capillary DBS and venous blood samples (EDTA tube and tube without additives) were collected from twenty healthy volunteers (12F/8M). From both venous blood samples, DBS were prepared volumetrically. Samples were analyzed using in-house developed LC-MS/MS methods for testosterone, androstenedione, 17-hydroxyprogesterone (17-OHP), cortisol, cortisone, corticosterone, and for dehydroepiandrosterone sulfate (DHEA-S).

RESULTS

DBS made from venous blood collected in EDTA tubes compared with capillary blood showed a correlation coefficient of ≥ 0.89 for all steroid hormones except corticosterone (0.67). DBS made from venous blood collected in tubes without additives showed a strong correlation with both DBS made from venous blood collected in EDTA tubes (≥0.97 for all steroid hormones) and capillary DBS (>0.90) except corticosterone (0.64).

CONCLUSION

DBS prepared from (residual) venous blood collected in EDTA blood tubes can be used for future development and validation of LC-MS/MS methods to quantify steroid hormones, except for corticosterone, in capillary DBS.

Development and validation of an LC-MS/MS multiplex assay for the quantification of bedaquiline, n-desmethyl bedaquiline, linezolid, levofloxacin, and clofazimine in dried blood spots

Dried blood spot (DBS) assays to quantify novel and repurposed drugs for the treatment of rifampicin-resistant tuberculosis (RR-TB) would facilitate pharmacokinetic studies and therapeutic drug monitoring in low-middle income settings, considering their ease of application and simple sample storage requirements. We describe a DBS method for the simultaneous quantification of bedaquiline and metabolite N-desmethyl bedaquiline, linezolid, levofloxacin, and clofazimine. The analytes were extracted from the matrix and isolated by solid-phase extraction. Two LC-MS/MS systems were used, optimized for the separate analysis of the more polar compounds (linezolid and levofloxacin), and less polar compounds (bedaquiline, N-desmethyl bedaquiline, and clofazimine), employing gradient elution. Electrospray ionization and multiple reaction monitoring were used to quantify the analytes on a Sciex API3200 and an API5500 triple quadrupole mass spectrometer, for the more polar and less polar analytes, respectively. Isotopically labelled internal standards were used to compensate for variability in the quantification of each analyte. The method was validated according to international guidelines and applied to samples from a clinical trial. We performed correlation and agreement analysis of the DBS assay and in-house plasma methods using Deming regressions and Bland-Altman plots. Coefficients of correlation between measured plasma and DBS concentrations ranged from 0.866 (95% CI: 0.817-0.902) to 0.989 (95% CI: 0.985-0.992). More than 67% of the samples showed a difference between the observed and estimated plasma concentrations within 20% of their means, meeting EMA requirements for method reproducibility and demonstrating the interchangeability of our DBS and plasma LC-MS/MS methods.

Development and validation of a quantification method for direct oral anticoagulants from capillary blood using volumetric absorptive microsampling and online SPE-LC-MS

The number of prescriptions for new direct oral anticoagulants (DOACs) apixaban, edoxaban, rivaroxaban and dabigatran has increased exponentially in recent years, increasingly replacing the old gold standard, vitamin-K-antagonists. Due to their wide therapeutic range, therapeutic drug monitoring (TDM) is not required, although it has been proven that this could significantly reduce side effects. In order to develop a cost-efficient and simple method for the simultaneous detection of the DOACs and phenprocoumon, a new technology for sample preparation from capillary blood in the ambulant sector named VAMS® was integrated and an LC-MS detector with on-line solid phase extraction (SPE) applying a Turboflow HTLC CycloneTM 1.0x50 mm column was used. The mobile phase consisted of methanol with water (3/97 v/v) and 0.1 % ammonia solution with a flow rate of 2.5 mL/min. For the chromatographic separation, a Phenomenex LTD Kinetex 2.6 µm C18 100 Å, 100x3.0 mm column with a flow rate of 0.3 mL/min in gradient mode was utilized. The mobile phase consisted of acetonitrile, water and formic acid (A: 10:90:0.1 v/v and B: 95:05:0.1 v/v). The method was fully validated in the therapeutic range of the substances according to current guidelines. The LLOQ ranged from 3.5 µg/L for rivaroxaban to 88 µg/L for phenprocoumon and the intra-day and inter-day precision was less than 13 % and 12 %, while the accuracy was within a range of 85.7-113 % and 88.7-106 %, respectively. Samples could be stored in the Mitra® devices for at least seven days at room temperature except of dabigatran. Because the Mitras® were used, exactly 10 µL of blood could be drawn and no significant haematocrit effect was observed. A reliable, simple and cost-effective extraction and analysis LC-MS method could be developed and validated. This method is therefore applicable in ambulatory care.

Volumetric absorptive microsampling meets electromembrane extraction for the first time: Case example of doxorubicin and its metabolite in whole blood samples

BACKGROUND

Microsampling of biological fluids followed by innovative sample pre-treatment reflects trends in bioanalytical chemistry. Volumetric absorptive microsampling (VAMS) enables exact whole blood volume collection and reduces the impact of hematocrit on the assay. In animal studies, it complies with the 3R principles (refine, reduce, replace). It allows for a gentle bleeding technique and a reduction in the number of laboratory animals by enabling ethically acceptable repeated blood collection from a single animal. Treating VAMS tips with electromembrane extraction (EME) in 96-well format offers a smart combination of non-invasive, low-volume blood collection with effective, environmentally friendly sample clean-up.

RESULTS

This study introduces the first application of EME in 96-well format for direct isolation of analytes from 10 μL of whole blood collected onto a VAMS device. Doxorubicin, a clinically used anticancer drug also utilized in cancer/cardio-oncology research involving rodents, where microsampling offers important advantages, and its metabolite doxorubicinol, were selected as relevant analytes. The optimized EME yielded reproducible recoveries for both analytes regardless of hematocrit levels, different anticoagulants, or free multivalent ions in the sample. Compared to conventional VAMS tips treatment, EME reduced matrix effects, increased throughput, and an environmental friendliness of the extraction. The EME followed by the UHPLC-MS/MS assay was validated for both analytes in whole blood absorbed onto VAMS tips. The same protocol was implemented to treat plasma to determine the blood-to-plasma ratio of the analytes in the same experiments. The practical utility was demonstrated by analyzing real samples collected from the doxorubicin-treated nude mice.

SIGNIFICANCE

The study offers a novel assay combining whole blood microsampling and sample clean-up in microextraction scale for preclinical pharmacokinetic studies with doxorubicin in rodents and for pharmacokinetic/pharmacodynamic modeling. This advancement in bioanalytical chemistry promotes scalable environmentally friendly procedures compatible with the 3R ethical principles in animal studies. Moreover, the concept of direct VAMS tips treatment with EME may also be easily translatable to clinical settings.

A comprehensive approach for detection of biotin deficiency from dried blood spot samples using liquid chromatography-mass spectrometry

Aim: The aim of the present study is to develop a liquid chromatography-mass spectrometry method to measure two important biomarkers of biotin deficiency from dried blood spot samples for effective management of the disorder. Materials & methods: The method was developed on a liquid chromatography-mass spectrometry system using pentafluorophenyl column employing a mobile phase composition of methanol and water in the isocratic mode. A full validation of the method was performed as per relevant guidelines. Results & conclusion: Correlation between the results of dried blood spot and plasma method was evaluated to determine the interconvertibility of the method. The developed method was successfully applied for establishing the reference ranges for these biomarkers in the population of Udupi, a coastal district of South India.

Personalization of pharmacotherapy with sirolimus based on volumetric absorptive microsampling (VAMS) in pediatric renal transplant recipients-from LC-MS/MS method validation to clinical application

BACKGROUND

The benefits of pharmacotherapy with sirolimus (SIR) in pediatric transplant recipients are well established. Traditionally, whole blood samples have been used to measure SIR concentrations. Volumetric Absorptive Microsampling (VAMS) is an alternative sampling strategy suitable for Therapeutic Drug Monitoring (TDM). In this study, we developed and validated two liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods for determining SIR concentrations in whole blood (WB) and capillary whole blood samples collected using a VAMS-Mitra™ device.

METHODS

We used protein precipitation during WB sample preparation and dispersive liquid-liquid microextraction (DLLME) with methyl tert-butyl ether for VAMS sample preparation to optimise the analyte extraction process. The described validation protocols were cross-validated, confirming the equivalence of the whole-blood and VAMS-based methods. Furthermore, the developed methods were evaluated in two three-level rounds of an external proficiency-testing scheme.

RESULTS

The analytical methods were successfully validated within the calibration range of SIR (0.5-60 ng/ml). The validation parameters met the European Medicines Agency (EMA) and the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDM&CT) acceptance criteria. No hematocrit (tested in the range of 24.3-64.1%), matrix, or carry-over effects were observed. Cross-validation confirmed the interchangeability between VAMS-LC-MS/MS and WB-LC-MS/MS methods. The developed methods were successfully implemented for SIR determination in 140 clinical samples (70 each of WB and VAMS) from pediatric renal transplant recipients, demonstrating their practicality and reliability.

CONCLUSION

The VAMS-based method has been rigorously tested and is clinically equivalent to the reference WB-LC-MS/MS method. Additionally, clinical validation confirmed the utility of the presented methods for TDM of the SIR in the pediatric population after renal transplantation.

Model-informed precision dosing: State of the art and future perspectives

Model-informed precision dosing (MIPD) stands as a significant development in personalized medicine to tailor drug dosing to individual patient characteristics. MIPD moves beyond traditional therapeutic drug monitoring (TDM) by integrating mathematical predictions of dosing and considering patient-specific factors (patient characteristics, drug measurements) as well as different sources of variability. For this purpose, rigorous model qualification is required for the application of MIPD in patients. This review delves into new methods in model selection and validation, also highlighting the role of machine learning in improving MIPD, the utilization of biosensors for real-time monitoring, as well as the potential of models integrating biomarkers for efficacy or toxicity for precision dosing. The clinical evidence of TDM and MIPD is discussed for various medical fields including infection medicine, oncology, transplant medicine, and inflammatory bowel diseases, thereby underscoring the role of pharmacokinetics/pharmacodynamics and specific biomarkers. Further research, particularly randomized clinical trials, is warranted to corroborate the value of MIPD in enhancing patient outcomes and advancing personalized medicine.

Rapid and non-invasive analysis of paracetamol overdose using paper arrow-mass spectrometry: a prospective observational study

BACKGROUND

Paracetamol is the most consumed medicine globally. Its accessibility contributes to common overdose. Paracetamol overdose is responsible for > 50% of acute liver failure cases, making it the second most common reason for a liver transplant. Rapid quantitation of paracetamol is crucial to guide treatment of paracetamol overdose. Current tests require invasive sampling and relatively long turnaround times. Paper arrow-mass spectrometry (PA-MS) combines sample collection, extraction, separation, enrichment and ionisation onto a single paper strip, achieving rapid, accurate, cost-effective and eco-friendly analysis direct from raw human saliva.

METHODS

To validate PA-MS against an established test, 17 healthy adults were recruited. Samples were collected before and at 15, 30, 60, 120 and 240 min after ingesting 1 g of paracetamol. Plasma measured with an established clinical test served as the reference standard to validate PA-MS with three biofluids-plasma, resting saliva (RS) and stimulated saliva (SS). Participants' views of blood, RS and SS sampling procedures were assessed qualitatively. Cross-validation was assessed using Lin's concordance correlation coefficients (CCC), Bland-Altman difference plots, and ratios of PA-MS to the reference standard test.

RESULTS

PA-MS using stimulated saliva offers a reliable alternative to intravenous blood sampling. The CCC is 0.93, the mean difference with the reference test is - 0.14 mg/L, and the ratios compared to the reference test are 0.84-1.27 from correlated samples collected at 5 intervals over 4 h for each participant.

CONCLUSIONS

Paracetamol detection from SS with PA-MS provides a reliable result that can aid timely treatment decisions. Differences between paracetamol concentration in resting and stimulated saliva were also identified for the first time, highlighting the importance of standardising saliva collection methods in general. This study marks a major milestone towards rapid and convenient saliva analysis.

Evaluation of Short-Term Stability of Different Nitazenes Psychoactive Opioids in Dried Blood Spots by Liquid Chromatography-High-Resolution Mass Spectrometry

Nitazenes represent a new synthetic opioids sub-class belonging to new psychoactive substances (NPSs). Their high pharmacological potency has led to numerous intoxications and fatalities, even at minimum doses. The aim of this study was to assess the stability of four nitazenes (etazene, flunitazene, isotonitazene and protonitazene) in dried blood spot (DBS) samples at different storage temperatures (room temperature and 4 °C) and determine the optimal storage conditions. Moreover, we developed and validated a new and fast liquid chromatography-high-resolution mass spectrometry method by the optimization of chromatographic conditions with the use of a different chromatographic column and mobile phases. Two concentrations, 1 and 5 ng/mL, were chosen based on the available data on nitazenes-related intoxications and their stability was evaluated at days 0 (control), 1, 7 and 30. The results showed that all analytes at 1 ng/mL were not detectable after 30 days at room temperature; a similar pattern was observed for 1 ng/mL etazene and isotonitazene samples when stored at 4 °C, whereas flunitazene and protonitazene decreased to a mean of 66% and 69% initial concentrations, respectively, at day 30. Differently, all analytes at 5 ng/mL were quantified above 44% and 41% initial concentrations at room temperature and 4 °C, respectively, showing a higher stability. The study of nitazenes stability in DBSs represents an important tool to determine the optimal sample storage conditions, such as temperature and time between sample collection and analysis. In contrast to another study, our study showed distinct stability behaviors for every investigated analyte, which also depended on the concentration. Therefore, it is difficult to define an optimal storage condition acceptable for all nitazenes. Room temperature proved to be the best medium- and long-term storage conditions for the highest concentrations, but the stability of low levels of flunitazene and protonitazene improved at 4 °C.

Liquid chromatography-mass spectrometric method for the simultaneous analysis of branched-chain amino acids and their ketoacids from dried blood spot as secondary analytes for the detection of maple syrup urine disease

Background

Maple syrup urine disease (MSUD) is an aminoacidopathy caused by a defective branched-chain alpha-ketoacid dehydrogenase complex, leading to the accumulation of branched-chain amino acids (BCAAs) and their respective keto acids (BCKAs). A comprehensive test was developed to measure BCAAs and BCKAs using LC-MS from dried blood spot (DBS) samples for the diagnosis and prevention of MSUD in newborns and infants.

Methods

Analytes were extracted from DBS using a methanol:0.1 % v/v formic acid solution (75:25) containing internal standards and analyzed on a Luna PFP column (150 mm × 4.6 mm, 3 µm) at a flow rate of 0.3 mL/min. The method was validated for linearity, accuracy, precision, recovery, carry-over, matrix effect, hematocrit, blood volume, and punch position effects. Biomarker stability in the matrix and stock solution was assessed. Correlation with the plasma method was determined using Pearson's correlation coefficient and Bland-Altman analysis. The method established reference ranges for the Udupi district population in South India.

Results

The method demonstrated linearity (r2 > 0.99), with a lower limit of detection at 2 µM (BCAA) and 1 µM (BCKA), and acceptable recovery of QC samples. Hematocrit, blood volume, punch position, and storage condition effects were within acceptable limits. Correlation and Bland-Altman analysis showed strong interconvertibility between plasma and DBS assays. Reference ranges for leucine, isoleucine, valine, KIC, KIV, and KMV were established.

Conclusion

The developed DBS method, requiring no derivatization and involving simple sample preparation with short run times, is a cost-effective and reliable approach for the confirmatory diagnosis of MSUD.

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Dried Blood Spot Sampling for Monitoring Children With Immune-Mediated Glomerulopathies and After Kidney Transplantation

Introduction

Monitoring kidney function and immunosuppressant levels in children post-kidney transplantation or those with glomerulopathies is challenging due to frequent venipunctures and clinic visits. Capillary dried blood spot sampling (DBS) offers a potential alternative.

Methods

In this prospective single-center study, 89 children (38% female and 62% male) requiring therapeutic drug monitoring (TDM) and kidney function assessment were enrolled. Of the patients, 79% were kidney transplant recipients, and 21% had immune-mediated glomerulopathies. The mean age was 13.4 (range, 5.7-18.0) years. DBS and standard venous serum samples were collected simultaneously for tacrolimus (TAC), cyclosporine A (CsA), everolimus (EVR), and creatinine levels. Furthermore, patient feedback on pain perception and feasibility was collected via questionnaire.

Results

No significant differences in parameter values between DBS and standard methods were observed (creatinine, -1.7 ± 14.5 μmol/l; EVR, 0.1 ± 1.2 μg/l; TAC, 0.3 ± 1.1 μg/l; CsA, 2.8 ± 9.8 μg/l). DBS demonstrated sufficient accuracy compared with standard methods. Patients favored DBS and telehealth consultations, especially due to less travel and school absences. Patients preferred finger pricking over ear pricking.

Conclusion

Capillary DBS proves reliable for TDM and kidney function assessment in pediatric kidney disease. It reduces patient and family burden compared with venous blood collection and enables telehealth consultations.

Toward a Clinical Decision Support System for Monitoring Therapeutic Antituberculosis Medical Drugs in Tanzania (Project TuberXpert): Protocol for an Algorithm' Development and Implementation

BACKGROUND

The end tuberculosis (TB) strategy requires a novel patient treatment approach contrary to the one-size-fits-all model. It is well known that each patient's physiology is different and leads to various rates of drug elimination. Therapeutic drug monitoring (TDM) offers a way to manage drug dosage adaptation but requires trained pharmacologists, which is scarce in resource-limited settings.

OBJECTIVE

We will develop an automated clinical decision support system (CDSS) to help practitioners with the dosage adaptation of rifampicin, one of the essential medical drugs targeting TB, that is known for large pharmacokinetic variability and frequent suboptimal blood exposure. Such an advanced system will encourage the spread of a dosage-individualization culture, including among practitioners not specialized in pharmacology. Thus, the objectives of this project are to (1) develop the appropriate population pharmacokinetic (popPK) model for rifampicin for Tanzanian patients, (2) optimize the reporting of relevant information to practitioners for drug dosage adjustment, (3) automate the delivery of the report in line with the measurement of drug concentration, and (4) validate and implement the final system in the field.

METHODS

A total of 3 teams will combine their efforts to deliver the first automated TDM CDSS for TB. A cross-sectional study will be conducted to define the best way to display information to clinicians. In parallel, a rifampicin popPK model will be developed taking advantage of the published literature, complemented with data provided by existing literature data from the Pan-African Consortium for the Evaluation of Antituberculosis Antibiotics (panACEA), and samples collected within this project. A decision tree will be designed and implemented as a CDSS, and an automated report generation will be developed and validated through selected case studies. Expert pharmacologists will validate the CDSS, and finally, field implementation in Tanzania will occur, coupled with a prospective study to assess clinicians' adherence to the CDSS recommendations.

RESULTS

The TuberXpert project started in November 2022. In July 2024, the clinical study in Tanzania was completed with the enrollment of 50 patients to gather the required data to build a popPK model for rifampicin, together with a qualitative study defining the report design, as well as the CDSS general architecture definition.

CONCLUSIONS

At the end of the TuberXpert project, Tanzania will possess a new tool to help the practitioners with the adaptation of drug dosage targeting complicated TB cases (TB or HIV, TB or diabetes mellitus, and TB or malnutrition). This automated system will be validated and used in the field and will be proposed to other countries affected by endemic TB. In addition, this approach will serve as proof of concept regarding the feasibility and suitability of CDSS-assisted TDM for further anti-TB drugs in TB-burdened areas deprived of TDM experts, including second-line treatments considered important to monitor.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/58720.

Advancing towards practice: A novel LC-MS/MS method for detecting retinol in dried blood spots

BACKGROUND

To date, clinical laboratories face challenges in quantifying retinol from DBS samples. Disputes arise throughout the whole detection process, encompassing the storage condition, the release strategy as well as the selection of internal standards.

METHODS

We incubated DBS with ascorbic acid solution. Then, retinol-d4 in acetonitrile was introduced to incorporate isotopic internal standard and promote protein precipitation. Afterward, sodium carbonate solution was added to ionize cytochromes (such as bilirubin), which amplified the difference of their hydrophobicity to retinol. Subsequently, cold-induced phase separation could be facilitated to separate retinol from the impurities. In the end, the upper layer was injected for LC-MS/MS analysis.

RESULTS

By comparing the detected retinol content in whole blood and DBS samples prepared from the same volume, we confirmed the established pretreatment was capable to extract most of retinol from DBS (recovery >90 %). Thereafter, we verified that within DBS, retinol possessed satisfying stability without antioxidation. Indoor-light exposure and storage duration would not cause obvious degradation (<10 %). Following systematic validation, the established method well met the criteria outlined in the relevant guidelines. After comparing with detected DBS results to the paired plasma samples, 54 out of 60 met the acceptance limit for cross-validation of ±20 %.

CONCLUSIONS

We realized precise quantification of retinol from one 3.2 mm DBS disc. By circumventing conventional antioxidation, liquid-liquid/solid-phase extraction and organic solvent evaporation, the pretreatment could be completed within 15 min consuming only minimal amounts of low-toxicity chemicals (ascorbic acid, acetonitrile, and sodium carbonate). We expect this contribution holds the potential to significantly facilitate the evaluation of patients' vitamin A status by using DBS samples in the future.

Quantification of Letrozole, Palbociclib, Ribociclib, Abemaciclib, and Metabolites in Volumetric Dried Blood Spots: Development and Validation of an LC-MS/MS Method for Therapeutic Drug Monitoring

Therapeutic drug monitoring (TDM) may be beneficial for cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), such as palbociclib, ribociclib, and abemaciclib, due to established exposure-toxicity relationships and the potential for monitoring treatment adherence. Developing a method for quantifying CDK4/6is, abemaciclib metabolites (M2, M20), and letrozole in dried blood spots (DBS) could be useful to enhance the feasibility of TDM. Thus, an optimized LC-MS/MS method was developed using the HemaXis DB10 device for volumetric (10 µL) DBS collection. Chromatographic separation was achieved using a reversed-phase XBridge BEH C18 column. Detection was performed with a triple quadrupole mass spectrometer, utilizing ESI source switching between negative and positive ionization modes and multiple reaction monitoring acquisition. Analytical validation followed FDA, EMA, and IATDMCT guidelines, demonstrating high selectivity, adequate sensitivity (LLOQ S/N ≥ 30), and linearity (r ≥ 0.997). Accuracy and precision met acceptance criteria (between-run: accuracy 95-106%, CV ≤ 10.6%). Haematocrit independence was confirmed (22-55%),with high recovery rates (81-93%) and minimal matrix effects (ME 0.9-1.1%). The stability of analytes under home-sampling conditions was also verified. Clinical validation supports DBS-based TDM as feasible, with conversion models developed for estimating plasma concentrations (the reference for TDM target values) of letrozole, abemaciclib, and its metabolites. Preliminary data for palbociclib and ribociclib are also presented.

Dried Blood Spot Method Development and Clinical Validation for the Analysis of Elexacaftor, Elexacaftor-M23, Tezacaftor, Tezacaftor-M1, Ivacaftor, Ivacaftor Carboxylate, and Hydroxymethyl Ivacaftor Using LC-MS/MS

BACKGROUND

The highly effective Cystic Fibrosis Transmembrane conductance Regulator (CFTR) modulator, elexacaftor-tezacaftor-ivacaftor, is now widely being used by people with cystic fibrosis. However, few independent studies have detailed the pharmacokinetics (PK) of CFTR modulators. Blood collection by venipuncture is the gold standard for PK measurements, but it is invasive. The aim of this study was to develop and clinically validate a quantification method for elexacaftor, tezacaftor, ivacaftor, and their main metabolites in dried blood spots (DBSs) using liquid chromatography with tandem mass spectrometry.

METHODS

Linearity, accuracy, precision, stability, hematocrit (Hct), spot-to-spot carryover, spot volume, and extraction efficiency were validated in DBS for all analytes. The clinical validation of elexacaftor-tezacaftor-ivacaftor in patients was performed by comparing 21 DBS samples with matched plasma samples.

RESULTS

The preset requirements for linearity, within-run and between-run accuracy, precision, Hct, spot volume, and extraction efficiency were met. Puncher carryover was observed and resolved by punching 3 blanks after each sample. The samples remained stable and showed no notable degradation across the tested temperatures and time intervals. Corrected DBS values with the Passing-Bablok regression equation showed good agreement in Bland-Altman plots, and acceptance values were within 20% of the mean for a minimum of 67% of the repeats, according to the EMA guidelines.

CONCLUSIONS

A quantification method for the analysis of elexacaftor, tezacaftor, ivacaftor, and their main metabolites was developed and clinically validated in DBS. This method could be valuable in both clinical care and research to address unanswered PK questions regarding CFTR modulators.

Analytical and clinical validation of an LC-MS/MS method for carbamazepine, lamotrigine and levetiracetam in dried blood spots

OBJECTIVES

Therapeutic drug monitoring is performed routinely in patients on anti-epileptic drugs (AEDs) for optimisation and individualisation of therapy. The dried blood spot (DBS) sampling technique is a suitable, more patient-friendly alternative for conventional venous sampling methods. However, before DBS can be used in routine care, data are needed to establish the correlation between standard plasma concentrations obtained from venous puncture and concentrations measured through DBS obtained by finger prick. This study aims to investigate the correlation between carbamazepine, lamotrigine and levetiracetam drug concentrations in venous blood and DBS samples in the same patients at the same time.

METHODS

Clinical validation was conducted by direct comparison of paired DBS and venous plasma samples. Method agreement was evaluated using Passing-Bablok regression analysis and Bland-Altman plots to provide insight into the relationship between the two analytically validated methods. For Bland-Altman analysis the acceptance limit required by both FDA and EMA guidelines is at least two-thirds (67%) of the paired samples within 80-120% of the mean of both methods.

RESULTS

Paired samples from 79 patients were studied. For all three AEDs, plasma and DBS concentrations correlated highly (r=0.90 for carbamazepine, r=0.93 for lamotrigine and r=0.93 for levetiracetam), indicating a linear relationship. For carbamazepine and lamotrigine, no proportional or constant bias was revealed. For levetiracetam, concentrations were higher in plasma samples than in DBS (slope 1.21), implying a conversion factor is needed. The acceptance limit was met for carbamazepine and levetiracetam with a value of 72% and 81%, respectively. For lamotrigine, this acceptance limit was not met with a value of 60%.

CONCLUSIONS

The method was successfully validated and will be used for therapeutic drug monitoring in patients using carbamazepine, lamotrigine and/or levetiracetam.

A novel approach to therapeutic drug monitoring of Ciclosporin in pediatric renal transplant recipients using volumetric absorptive microsampling (VAMS) - Teaching old dog new tricks

BACKGROUND AND AIMS

Ciclosporin (CSA) is an immunosuppressive agent that requires therapeutic drug monitoring (TDM). High partitioning in erythrocytes indicates that whole blood (WB) is a suitable matrix for CSA determination. Alternative sampling strategies, such as volumetric absorptive microsampling (VAMS), are novel possibilities for blood collection during TDM for various analytes, including immunosuppressants. This technique is attractive for vulnerable pediatric patients, including home-based self-sampling, remote therapy, and adherence control.

MATERIALS AND METHODS

This study aimed to develop and validate a new method for CSA determination based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) of WB and VAMS samples. Additionally, these methods were applied for CSA determination in clinical samples from pediatric transplant recipients. A strong point of this study is the assessment of an external proficiency testing scheme.

RESULTS

Both methods were successfully validated within the 1-2000 ng/mL calibration range, with LOD 0.5 and 1 ng/mL for WB and VAMS methods, respectively. All the validation parameters fulfilled the international acceptance criteria for bioanalytical methods. Cross-validation confirmed the interchangeability of the LC-MS/MS method developed in this study.

CONCLUSION

This study developed and validated novel methods for CSA determination in whole blood and VAMS using LC-MS/MS. Clinical validation and proficiency testing confirmed their utility in routine clinical practice.

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.

Assessment of Dried Serum Spots (DSS) and Volumetric-Absorptive Microsampling (VAMS) Techniques in Therapeutic Drug Monitoring of (Val)Ganciclovir-Comparative Study in Analytical and Clinical Practice

Ganciclovir (GCV) and its prodrug valganciclovir (VGCV) are antiviral medications primarily used to treat infections caused by cytomegalovirus (CMV), particularly in immunocompromised individuals such as solid organ transplant (SOT) recipients. Therapy with GCV is associated with significant side effects, including bone marrow suppression. Therefore, therapeutic drug monitoring (TDM) is mandatory for an appropriate balance between subtherapeutic and toxic drug levels. This study aimed to develop and validate three novel methods based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) for GCV determination in serum (reference methodology), dried serum spots (DSS), and VAMS-Mitra™ devices. The methods were optimized and validated in the 0.1-25 mg/L calibration range. The obtained results fulfilled the EMA acceptance criteria for bioanalytical method validation. Assessment of DSS and VAMS techniques extended GCV stability to serum for up to a minimum of 49 days (at room temperature, with desiccant). Developed methods were effectively evaluated using 80 clinical serum samples from pediatric renal transplant recipients. Obtained samples were used for DSS, and dried serum VAMS samples were manually generated in the laboratory. The results of GCV determination using serum-, DSS- and VAMS-LC-MS/MS methods were compared using regression analysis and bias evaluation. The conducted statistical analysis confirmed the interchangeability between developed assays. The DSS and VAMS samples are more accessible and stable during storage, transport and shipment than classic serum samples.

Analytical Validation of a Volumetric Absorptive Microsampling Method for Therapeutic Drug Monitoring of the Oral Targeted Anticancer Agents, Abiraterone, Alectinib, Cabozantinib, Imatinib, Olaparib, and Sunitinib, and Metabolites

BACKGROUND

Volumetric Absorptive Microsampling (VAMS) is a useful tool for therapeutic drug monitoring (TDM) of oral targeted anticancer agents. VAMS aims to improve safety and efficacy by enabling at-home blood sample collection by patients. This study aimed to develop and validate an ultra-high performance liquid chromatography-tandem mass spectrometry method for the quantitative determination of abiraterone, alectinib, cabozantinib, imatinib, olaparib, sunitinib, and the metabolites, Δ(4)-abiraterone (D4A), alectinib-M4, imatinib-M1, and N -desethyl sunitinib, in dried whole blood samples using VAMS to support TDM.

METHODS

After the collection of 10 μL of whole blood sample using the VAMS device, the analytes were extracted from the tip using methanol with shaking, evaporated, and reconstituted in acetonitrile:0.1 mol/L ammonium hydroxide in water (1:1, vol/vol). The extracts were then analyzed using ultra-high performance liquid chromatography-tandem mass spectrometry. Validation experiments based on the ICH M10 guideline were carried out, and stability was evaluated under shipping and storage conditions. VAMS specimens were collected in the outpatient clinic to demonstrate the applicability of the assay.

RESULTS

The validated range of the method was considered accurate and precise for all analytes. Accordingly, the validation experiments met the relevant requirements, except for cross-analyte interference. Based on the stability data, shipment can be performed at room temperature within 14 days after sample collection and the VAMS specimen can be stored up to 9 months at -20 and -70°C. Samples from 59 patients were collected at the hospital.

CONCLUSIONS

The developed method could be used to successfully quantify the concentrations of abiraterone, D4A, alectinib, alectinib-M4, cabozantinib, imatinib, imatinib-M1, olaparib, sunitinib, and N -desethyl sunitinib within the validated range using VAMS. Therefore, the method can be used to estimate the dried whole blood-to-plasma ratios for TDM in the clinic.

Therapeutic drug monitoring of osimertinib in EGFR mutant non-small cell lung cancer by dried blood spot and plasma collection: A pilot study

AIMS

Therapeutic drug monitoring (TDM) has led to significant improvements in individualized medical care, although its implementation in oncology has been limited to date. Tyrosine kinase inhibitors (TKIs) are a group of therapies for which TDM has been suggested. Osimertinib is one such therapy used in the treatment of epidermal growth factor receptor (EGFR) mutation-driven lung cancer. Herein, we describe a prospective pilot study involving 21 patients on osimertinib primarily as a preliminary evaluation of drug levels in a real-world setting.

METHODS

Concentrations of the drug and its primary metabolites were measured with a validated liquid chromatography-mass spectrometry (LC-MS) assay across serial timepoints. As part of this study, inter-individual variability by dose and ethnicity as well as intra-individual variability across timepoints are explored. Furthermore, we attempted to validate dried blood spot (DBS)-based quantitation as an accurate alternative to plasma quantitation.

RESULTS

Successful quantitation of osimertinib and primary metabolites was achieved for our subjects. Compound plasma levels were highly correlated to DBS levels. There was no significant difference in concentrations with ethnicity or dosing or intra-individual variability across timepoints.

CONCLUSIONS

As such, we demonstrate that TDM for osimertinib is practical for future trials. We also validated the use of DBS as an alternative to conventional quantitation for exploration of TDM for osimertinib in larger trials and for other targeted therapies.

Nucleic acid degradation after long-term dried blood spot storage

Collecting and preserving biological samples in the field, particularly in remote areas in tropical forests, prior to laboratory analysis is challenging. Blood samples in many cases are used for nucleic acid-based species determination, genomics or pathogen research. In most cases, maintaining a cold chain is impossible and samples remain at ambient temperature for extended periods of time before controlled storage conditions become available. Dried blood spot (DBS) storage, blood stored on cellulose-based paper, has been widely applied to facilitate sample collection and preservation in the field for decades. However, it is unclear how long-term storage on this substrate affects nucleic acid concentration and integrity. We analysed nucleic acid quality from DBS stored on Whatman filter paper no. 3 and FTA cards for up to 15 years in comparison to cold-chain stored samples using four nucleic acid extraction methods. We examined the ability to identify viral sequences from samples of 12 free-ranging primates in the Amazon forest, using targeted hybridization capture, and determined if mitochondrial genomes could be retrieved. The results suggest that even after extended periods of storage, DBS will be suitable for some genomic applications but may be of limited use for viral pathogen research, particularly RNA viruses.

'Under pressure': The role of therapeutic drug monitoring in the treatment of hypertension

Antihypertensive drugs do not qualify as optimal candidates for therapeutic drug monitoring (TDM), given their obvious physiological effect, the absence of a clear relationship between drug concentrations and pharmacodynamic outcomes and their wide therapeutic range. However, since non-adherence is a major challenge in hypertension management, using drug concentrations can be of value to identify non-adherence as a first step towards better blood pressure control. In this article we discuss the key challenges associated with measuring and interpreting antihypertensive drug concentrations that are important when TDM is used to improve non-adherence. Additionally, we elaborate on the role of TDM in optimizing antihypertensive drug treatment besides addressing non-adherence by highlighting its value in specific patient groups with altered pharmacokinetic parameters such as female vs. male or elderly patients.

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

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

Removing the physician from the equation: Patient-controlled, home-based therapeutic drug self-monitoring of tacrolimus

The dosing of tacrolimus, which forms the backbone of immunosuppressive therapy after kidney transplantation, is complex. This is due to its variable pharmacokinetics (both between and within individual patients), narrow therapeutic index, and the severe consequences of over- and underexposure, which may cause toxicity and rejection, respectively. Tacrolimus is, therefore, routinely dosed by means of therapeutic drug monitoring (TDM). TDM is performed for as long as the transplant functions and frequent and often lifelong sampling is therefore the rule. This puts a significant burden on patients and transplant professionals and is associated with high healthcare-associated costs. Furthermore, by its very nature, TDM is reactive and has no predictive power. Finally, the current practice of TDM does not foresee in an active role for patients themselves. Rather, the physician or pharmacist prescribes the next tacrolimus dose after obtaining the concentration measurement test results. In this article, we propose a strategy of patient-controlled, home-based, self-TDM of the immunosuppressant tacrolimus after transplantation. We argue that with the combined use of population tacrolimus pharmacokinetic models, home-based sampling by means of dried blood spotting and implementation of telemedicine, this may become a feasible approach in the near future.

A Validated Assay to Quantify Osimertinib and Its Metabolites, AZ5104 and AZ7550, from Microsampled Dried Blood Spots and Plasma

BACKGROUND

Osimertinib is an oral small-molecule tyrosine kinase receptor inhibitor used to treat non-small cell lung cancer (NSCLC) with a sensitizing epidermal growth factor receptor mutation. Patients may experience drug toxicity and require dose deescalation. The study aimed to quantitate osimertinib and its 2 active metabolites, AZ5104 and AZ7550, in microsampled dried blood spots (DBS) collected from patients with NSCLC using a hemaPEN device and compare them with plasma drug levels.

METHODS

A 6-min ultrahigh-performance liquid chromatography-tandem mass spectrometry method was developed and validated using plasma and DBS. The accuracy, selectivity, matrix effect, recovery, and stability were assessed using bioanalytical validation criteria. The hematocrit effect was investigated in DBS. Drug levels were measured in 15 patients with NSCLC, and the Bland-Altman method was used to compare measurements between plasma and DBS.

RESULTS

The validated assay determined accurate and precise quantities, respectively, for osimertinib in both plasma (93.2%-99.3%; 0.2%-2.3%) and DBS (96.7%-99.6%; 0.5%-10.3%) over a concentration of 1-729 ng/mL. The osimertinib metabolites, AZ5104 and AZ7550, were similarly validated in accordance with bioanalytical guidelines. For 30%-60% patient hematocrit, no hematocrit bias was observed with DBS for all analytes. The Bland-Altman method showed high concordance between plasma and DBS analyte levels. Stability experiments revealed that osimertinib and its metabolites were poorly stable in plasma at room temperature, whereas all analytes were stable in DBS for 10 days at room temperature.

CONCLUSIONS

The measurement of osimertinib, AZ5104, and AZ7550 from hemaPEN microsampled DBS is a convenient and reliable approach for therapeutic drug monitoring that produces measurements consistent with plasma drug levels.

Determination of remifentanil in neonatal dried blood spots by liquid chromatography-tandem mass spectrometry

Remifentanil is an ultra-short-acting synthetic opioid-class analgesic which might be increasingly used "off-label" as pain management during labour. Side effects in parturients during labour, and in the infant at birth are of particular concern, especially respiratory depression which is concentration-dependent, and can occur at levels as low as 3-5 ng mL-1. The safety of such use, particularly in newborns due to remifentanil placental transfer, has not been fully demonstrated yet, partly due to the lack of a suitable non-invasive analytical method. The aim of our work was to develop a sensitive method to monitor the levels of remifentanil in neonates by a non-invasive sampling of umbi lical cord blood to support efficacy and safety trials. The presented LC-MS method is sensitive enough to reliably quantify remifentanil in just 20 µL of blood at only 0.3 ng mL-1. The dried blood spot sample preparation included solvent extraction with subsequent solid-phase extraction. The method was validated in terms of accuracy, precision, recovery, matrix effect, and stability, and was successfully applied to a small pilot study. The estimated arterial blood concentrations at the time of delivery ranged from 0.2 to 0.3, and up to 0.9 ng mL-1 in neonatal, and maternal samples, respectively.

Elexacaftor/tezacaftor/ivacaftor in liver or kidney transplanted people with cystic fibrosis using tacrolimus, a drug-drug interaction study

BACKGROUND

The use of elexacaftor/tezacaftor/ivacaftor (ETI) in people with cystic fibrosis (pwCF) after solid organ transplantation is controversial because of potential drug-drug interactions (DDI) with tacrolimus. We aimed to improve insight into the safety and clinical benefits of co-administration of ETI and tacrolimus in liver or kidney transplanted adult pwCF.

METHODS

In 5 pwCF, tacrolimus concentrations were monitored during 2 weeks before and 4 weeks after starting ETI treatment. Trough levels, area under the curve (AUC) and clinical effect of ETI were investigated. During the study (6 weeks in total) adverse events were monitored.

RESULTS

The DDI between tacrolimus and ETI resulted in an increased exposure of tacrolimus in all subjects, the dose adjusted AUC0-24h was 1.79 (median) times higher at the end of the study. Five dose adjustments were performed in 4 subjects in order to attain tacrolimus target range. No adverse events were reported and all subjects showed clinical improvement during ETI treatment.

CONCLUSION

The clinical value of ETI treatment in kidney and liver transplanted pwCF is clear. The use of ETI may increase tacrolimus levels moderately. Therefore, we recommend close monitoring of tacrolimus trough levels in patients who start ETI.

Microsampling Techniques Suitable for Therapeutic Drug Monitoring of Antipsychotics

BACKGROUND

Therapeutic drug monitoring (TDM) of antipsychotics for dose titration or detection of noncompliance is not uncommon in daily practice. Normally, TDM implies measuring a drug concentration in venous blood samples. This technique is invasive and requires trained assistants and patients normally need to go to an outpatient clinic. Over the past decades, sensitivity of analytical equipment has improved leading to a growing interest in microsampling techniques. These techniques are minimally invasive, require a small volume (<100 μL), usually result in stable samples, and can be collected by the patient or a caregiver at home. Before a microsampling technique can be used in daily routine, proper method development and a clinical validation study should be performed.

METHOD

For this review, the databases of PubMed and Embase were systematically searched. Currently available microsampling techniques for antipsychotics in blood, serum, or plasma are summarized. Subsequently, it has also been assessed whether these techniques are sufficiently validated for TDM monitoring in daily practice.

RESULTS

Several microsampling techniques are available today, for example, dried blood spot sampling, dried plasma extraction cards, and volumetric absorptive microsampling. Eighteen studies were identified in which a microsampling technique for 1 or a few antipsychotics was chemically analytically and clinically validated. However, the majority of these studies have relevant shortcomings that mean its usefulness for different antipsychotics is not yet well established.

CONCLUSIONS

Microsampling for TDM can be recommended for patients using clozapine. For TDM of other antipsychotics, it is a very promising development.

Towards clinical adherence monitoring of oral endocrine breast cancer therapies by LC-HRMS-method development, validation, comparison of four sample matrices, and proof of concept

Oral endocrine therapies (OET) for breast cancer treatment need to be taken over a long period of time and are associated with considerable side effects. Therefore, adherence to OET is an important issue and of high clinical significance for breast cancer patients' caregivers. We hypothesized that a new bioanalytical strategy based on liquid chromatography and high-resolution mass spectrometry might be suitable for unbiased adherence monitoring (AM) of OET. Four different biomatrices (plasma, urine, finger prick blood by volumetric absorptive microsampling (VAMS), oral fluid (OF)) were evaluated regarding their suitability for AM of the OET abemaciclib, anastrozole, exemestane, letrozole, palbociclib, ribociclib, tamoxifen, and endoxifen. An analytical method was developed and validated according to international recommendations. The analytical procedures were successfully validated in all sample matrices for most analytes, even meeting requirements for therapeutic drug monitoring. Chromatographic separation of analytes was achieved in less than 10 min and limits of quantification ranged from 1 to 1000 ng/mL. The analysis of 25 matching patient samples showed that AM of OET is possible using all four matrices with the exception of, e.g., letrozole and exemestane in OF. We were able to show that unbiased bioanalytical AM of OET was possible using different biomatrices with distinct restrictions. Sample collection of VAMS was difficult in most cases due to circulatory restraints and peripheral neuropathy in fingers and OF sampling was hampered by dry mouth syndrome in some cases. Although parent compounds could be detected in most of the urine samples, metabolites should be included when analyzing urine or OF. Plasma is currently the most suitable matrix due to available reference concentrations.

A validated method for simultaneous quantification of four antiretrovirals in dried blood spot and plasma using LC-MS/MS: Application to efavirenz therapeutic drug monitoring in pregnant patients

INTRODUCTION

The specific physiological background induced by pregnancy leads to significant changes in maternal pharmacokinetics, suggesting potential variability in plasma concentrations of antiretrovirals. Pregnant HIV patients exposed to subtherapeutic doses, particularly in the last trimester of the pregnancy, have higher chances to transmit the infection to their children. Therefore, the therapeutic drug monitoring of antiretrovirals in HIV pregnant patients would be of great value.

OBJECTIVES

This study aimed to develop and validate a sensitive liquid chromatograph tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of efavirenz, raltegravir, atazanavir, and ritonavir in dried blood spots (DBS) and plasma.

DESIGN AND METHODS

The analytes were extracted from the DBS punch and plasma with a mixture of methanol:zinc sulfate 200 mM (50:50, v/v) and 100 % methanol, respectively. For the chromatographic separation a Shim-pack® C18, 4.6 mm × 150 mm, 5 μm column was used. Detection was performed in a 3200-QTRAP® mass spectrometer, with a run time of 6 min.

RESULTS

The assay was linear in the range of 15-1,000 ng/mL for raltegravir, 50-10,000 ng/mL for both atazanavir and ritonavir, 50-5,000 ng/mL for efavirenz. Precision and accuracy at these concentrations were less than 15 % for all analytes. Raltegravir, atazanavir, and ritonavir were stable for seven days at 23 °C and 40 °C, whereas efavirenz was stable for twenty-four hours at the same conditions.

CONCLUSIONS

The method was successfully applied to quantify efavirenz in DBS samples obtained from HIV-1 infected pregnant volunteers under antiretroviral therapy. The concentrations of efavirenz in DBS and plasma were comparable according to Passing-Bablok regression and Bland-Altman analysis.