A multiple methods approach to determine adherence with prescribed mycophenolate in children with kidney transplant

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Microsampling techniques and patient-centric therapeutic drug monitoring of immunosuppressants

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

Non-adherence to immunosuppressive medications in kidney transplant recipients- a systematic scoping review

BACKGROUND

Rejection and graft failure remain common in kidney transplant recipients. Non-adherence to immunosuppressive medications is considered a major contributary factor to reduced long-term graft survival, particularly in younger people. Improvements in clinical practice based on adherence studies has been minimal.

METHODS

Joanna Briggs' Institute Methodology was used. MedlineALL, Embase, Web of Science Core Collection and Scopus databases were searched from January 2000 through to December 2023. Abstract and full text reviews were undertaken independently by two reviewers. Data was collated using a pre-designed extraction tool.

RESULTS

359 articles met the inclusion criteria. Non-adherence was commonly defined using self-reported questionnaires or pharmacy re-fill rates. Prevalence of non-adherence varied widely. There was little correlation between method of measurement and reported rates of non-adherence. Despite younger age being identified as a risk factor for non-adherence, pooled reported prevalence did not differ significantly in studies reporting prevalence in children, adolescents, or young adults vs. older adults (36.0 % vs. 34.0 %). Interventional studies to detect or improve adherence are highly heterogenous, often report small effects and are limited by the lack of gold-standard methods to measure adherence.

DISCUSSION

This scoping review outlines the complexities of non-adherence to immunosuppressive medications among kidney transplant recipients, highlighting significant variability in adherence definitions, measurements, and intervention efficacy. Reported non-adherence rates vary widely (2-89 %), underscoring the need for standardisation of the definition of non-adherence in research. Findings suggest that non-adherence to immunosuppressive medication is driven by a mix of demographic, psychosocial, and transplant-specific factors. Future research should prioritise standardised definitions of adherence, validated tools to measure adherence, and focus on clinically significant outcomes in non-adherent populations to develop meaningful, impactful interventions for long-term patient benefit.

A Systematic Literature Review on the Use of Dried Biofluid Microsampling in Patients With Kidney Disease

BACKGROUND

Kidney disease is fairly unique due to the lack of symptoms associated with disease activity, and it is therefore dependent on biological monitoring. Dried biofluids, particularly dried capillary blood spots, are an accessible, easy-to-use technology that have seen increased utility in basic science research over the past decade. However, their use is yet to reach the kidney patient population clinically or in large-scale discovery science initiatives. The aim of this study was to systematically evaluate the existing literature surrounding the use of dried biofluids in kidney research.

METHODS

A systematic literature review was conducted using three search engines and a predefined search term strategy. Results were summarised according to the collection method, type of biofluid, application to kidney disease, cost, sample stability and patient acceptability.

RESULTS

In total, 404 studies were identified and 67 were eligible. In total, 34,739 patients were recruited to these studies with a skew towards male participants (> 73%). The majority of samples were blood, which was used either for monitoring anti-rejection immunosuppressive drug concentrations or for kidney function. Dried biofluids offered significant cost savings to the patient and healthcare service. The majority of patients preferred home microsampling when compared to conventional monitoring.

CONCLUSION

There is an unmet need in bringing dried microsampling technology to advance kidney disease despite its advantages. This technology provides an opportunity to upscale patient recruitment and longitudinal sampling, enhance vein preservation and overcome participation bias in research.

Insights into adherence to medication and lifestyle recommendations in an international cohort of patients with catecholaminergic polymorphic ventricular tachycardia

AIMS

In patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a rare inherited arrhythmia syndrome, arrhythmic events can be prevented by medication and lifestyle recommendations. In patients who experience breakthrough arrhythmic events, non-adherence plays an essential role. We aimed to investigate the incidence and potential reasons for non-adherence to medication and lifestyle recommendations in a large, international cohort of patients with CPVT.

METHODS AND RESULTS

An online multilingual survey was shared with CPVT patients worldwide by their cardiologists, through peer-recruitment, and on social media from November 2022 until July 2023. Self-reported non-adherence was measured using the validated Medication Adherence Rating Scale (MARS) and a newly developed questionnaire about lifestyle. Additionally, validated questionnaires were used to assess potential reasons for medication non-adherence. Two-hundred-and-eighteen patients completed the survey, of whom 200 (92%) were prescribed medication [122 (61%) female; median age 33.5 years (interquartile range: 22-50)]. One-hundred-and-three (52%) were prescribed beta-blocker and flecainide, 85 (43%) beta-blocker, and 11 (6%) flecainide. Thirty-four (17%) patients experienced a syncope, aborted cardiac arrest or appropriate implantable cardioverter defibrillator shock after diagnosis. Nineteen (13.4%) patients were exercising more than recommended. Thirty (15%) patients were non-adherent to medication. Female sex [odds ratio (OR) 3.7, 95% confidence interval (CI) 1.3-12.0, P = 0.019], flecainide monotherapy compared to combination therapy (OR 6.8, 95% CI 1.6-31.0, P = 0.010), and a higher agreement with statements regarding concerns about CPVT medication (OR 1.2, 95% CI 1.1-1.3, P < 0.001) were independently associated with non-adherence.

CONCLUSION

The significant rate of non-adherence associated with concerns regarding CPVT-related medication, emphasizes the potential for improving therapy adherence by targeted patient education.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONSS

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

A Volumetric Absorptive Microsampling UPLC-MS/MS Method for Simultaneous Quantification of Tacrolimus, Mycophenolic Acid and Creatinine in Whole Blood of Renal Transplant Recipients

(1) Background: Continuous monitoring of tacrolimus (TAC), mycophenolic acid (MPA), and creatinine (Cre) after renal transplantation is vitally important. In this study, we developed a new method based on volumetric absorptive microsampling (VAMS) combined with Ultra Performance Liquid Chromatography−Tandem Mass Spectrometry (UPLC-MS/MS) to simultaneously quantify three analytes including TAC, MPA, and Cre in whole blood. (2) Methods: The VAMS-based UPLC-MS/MS assay used a shared extraction and a single injection to simultaneously quantify the included TAC, MPA, and Cre. Development and validation were carried out following the Food and Drug Administration and European Medicines Agency guidelines for the validation of bioanalytical methods. Moreover, clinical validation for the three analytes was performed in both dried blood spot (DBS) and VAMS. Furthermore, a willingness survey was conducted using the system usability scale (SUS) for renal transplant recipients. (3) Results: The assay was successfully validated for all analytes. No interference, carryover, or matrix effects were observed, and extraction recoveries and process efficiencies were >90.00%. Analysis was unaffected by hematocrit (0.20~0.60, L/L) and anticoagulants (EDTA-2K). Dried VAMS samples were stable for 7 days at ambient temperature and stable for at least 1 month at −20 °C. During clinical validation, the measured TAC, corrected MPA, and Cre concentrations of VAMS samples met the analytical standards (95.00%, 88.57%, and 92.50%). When more stringent clinical acceptance criteria were set, the results obtained by VAMS (90.00%, 71.43%, and 85.00%) better than DBS (77.50%, 62.86%, and 70.00%). Compared with DBS, the survey found that renal transplant recipients are more inclined to use VAMS. (4) Conclusions: A robust extraction and UPLC-MS/MS analysis method in VAMS tips was developed and fully validated for the simultaneous quantification of TAC, MPA, and Cre concentrations. This method provides analytical support for the one-sample remote monitoring of both immunosuppressive drug concentrations and renal function in allo-renal recipients. Based on the good consistency between this method and the routine detection of venous blood samples and higher patient satisfaction than DBS, we believe that VAMS sampling can be a better alternative to venous whole-blood sampling.

Volumetric microsampling for simultaneous remote immunosuppressant and kidney function monitoring in outpatient kidney transplant recipients

AIMS

Immunosuppressant and kidney function monitoring are crucial for kidney transplant recipient follow-up. Microsamples enable remote sampling and minimise patient burden as compared to conventional venous sampling at the clinic. We developed a liquid chromatography-tandem mass spectrometry assay to quantify tacrolimus, mycophenolic acid (MPA), creatinine and iohexol in dried blood spot (DBS), and volumetric absorptive microsample (VAMS) samples.

METHODS

The assay was successfully validated analytically for all analytes. Clinical validation was conducted by direct comparison of paired DBS, VAMS and venous reference samples from 25 kidney transplant recipients. Patients received iohexol 5-15 minutes before immunosuppressant intake and were sampled 0, 1, 2 and 3 hours thereafter, enabling tacrolimus and MPA area under the concentration-time curve (AUC) and creatinine-based and iohexol-based glomerular filtration rate (GFR) estimation. Method agreement was evaluated using Passing-Bablok regression, Bland-Altman analysis and the percentages of values within 15-30% of the reference (P15 -P30 ) with a P20 acceptance threshold of 80%.

RESULTS

For DBS samples, method agreement was excellent for tacrolimus trough concentrations (n = 25, P15  = 92.0%) and AUCs (n = 25; P20  = 95.8%) and adequate for creatinine-based GFR trend monitoring (n = 25; P20  = 80%). DBS-based MPA AUC assessment showed suboptimal agreement (n = 16; P20  = 68.8%), but was considered acceptable given its P30 of 100%. The assay performed inadequately for DBS-based iohexol GFR determination (n = 24; P20  = 75%). The VAMS technique generally showed inferior performance, but can be considered for certain situations.

CONCLUSION

The assay was successfully validated for tacrolimus, MPA and creatinine quantification in DBS samples, enabling simultaneous remote kidney function trend monitoring and immunosuppressant therapeutic drug monitoring in kidney transplant recipients.

Adherence to metformin in adults with type 2 diabetes: a combined method approach

Background

Medication adherence, one of the most important aspects in the process of optimal medicines use, is unfortunately still a major challenge in modern healthcare, and further research is required into how adherence can be assessed and optimised. The aim of this study was to use a combined method approach of self-report and dried blood spot (DBS) sampling coupled with population pharmacokinetic (PopPK) modelling, to assess adherence to metformin in adult patients with type 2 diabetes. Further aims were to assess metformin exposure levels in patients, determine factors associated with non-adherence with prescribed metformin, and to explore the relationship between adherence and therapeutic outcomes.

Methods

A combined method approach was used to evaluate metformin adherence in patients with type 2 diabetes who had been prescribed metformin for a minimum period of 6 months. Patients were recruited from consultant-led diabetic outpatient clinics at three hospitals in Northern Ireland, UK. Data collection involved self-reported questionnaires [Medication Adherence Report Scale (MARS), Beliefs about Medicines Questionnaire and Centre for Epidemiologic Studies Depression Scale], direct measurement of metformin concentration in DBS samples, and researcher-led patient interviews. The DBS sampling approach was coupled with population pharmacokinetic (PopPK) modelling, which took account of patient characteristics, metformin dosage and type of formulation prescribed (immediate or sustained release).

Results

The proportion of patients considered to be adherent to their prescribed metformin, derived from self-reported MARS scores and metformin concentration in DBS samples, was 61.2% (74 out of 121 patients). The majority (n = 103, 85.1%) of recruited patients had metformin exposure levels that fell within the therapeutic range. However, 17 patients (14.1%) had low exposure to metformin and one patient (0.8%) had undetectable metformin level in their blood sample (non-exposure). Metformin self-administration and use of a purchased adherence pill box significantly increased the probability of a patient being classified as adherent based on logistic regression analysis. Both HbA1c and random glucose levels (representing poor glycaemic control) in the present research were, however, not statistically linked to non-adherence to metformin (P > 0.05).

Conclusions

A significant proportion of participating patients were not fully adherent with their therapy. DBS sampling together with the use of a published PopPK model was a useful, novel, direct, objective approach to estimate levels of adherence in adult patients with type 2 diabetes (61.2%).

Supplementary Information

The online version contains supplementary material available at 10.1186/s40545-022-00457-5.

Recent Advances in Therapeutic Drug Monitoring of Voriconazole, Mycophenolic Acid, and Vancomycin: A Literature Review of Pediatric Studies

The review includes studies dated 2011-2021 presenting the newest information on voriconazole (VCZ), mycophenolic acid (MPA), and vancomycin (VAN) therapeutic drug monitoring (TDM) in children. The need of TDM in pediatric patients has been emphasized by providing the information on the differences in the drugs pharmacokinetics. TDM of VCZ should be mandatory for all pediatric patients with invasive fungal infections (IFIs). Wide inter- and intrapatient variability in VCZ pharmacokinetics cause achieving and maintaining therapeutic concentration during therapy challenging in this population. Demonstrated studies showed, in most cases, VCZ plasma concentrations to be subtherapeutic, despite the updated dosages recommendations. Only repeated TDM can predict drug exposure and individualizing dosing in antifungal therapy in children. In children treated with mycophenolate mofetil (MMF), similarly as in adult patients, the role of TDM for MMF active form, MPA, has not been well established and is undergoing continued debate. Studies on the MPA TDM have been carried out in children after renal transplantation, other organ transplantation such as heart, liver, or intestine, in children after hematopoietic stem cell transplantation or cord blood transplantation, and in children with lupus, nephrotic syndrome, Henoch-Schönlein purpura, and other autoimmune diseases. MPA TDM is based on the area under the concentration-time curve; however, the proposed values differ according to the treatment indication, and other approaches such as pharmacodynamic and pharmacogenetic biomarkers have been proposed. VAN is a bactericidal agent that requires TDM to prevent an acute kidney disease. The particular group of patients is the pediatric one. For this group, the general recommendations of the dosing may not be valid due to the change of the elimination rate and volume of distribution between the subjects. The other factor is the variability among patients that concerns the free fraction of the drug. It may be caused by both the patients' population and sample preconditioning. Although VCZ, MMF, and VAN have been applied in pediatric patients for many years, there are still few issues to be solve regarding TDM of these drugs to ensure safe and effective treatment. Except for pharmacokinetic approach, pharmacodynamics and pharmacogenetics have been more often proposed for TDM.

Adherence to laboratory testing in pediatric liver transplant recipients

BACKGROUND

The objectives of this retrospective cohort study are to describe rates of adherence to laboratory testing 6 months to 3 years post-liver transplantation and to examine demographic and clinical factors related to lab non-adherence and the association with medication adherence and clinical outcomes.

METHODS

Medical chart review was conducted for 54 youth (mean age = 5.0 years) transplanted between 2003 and 2014. Lab adherence (≥80%) was measured as the proportion of completed labs out of the number expected. Immunosuppressant drug-level variability was used as a proxy for medication adherence. Clinical outcomes included LAR, viral infection, hospitalization, and non-routine clinic visit ≥12 months after transplant.

RESULTS

Lab adherence decreased substantially over time. Single-parent household (aOR 5.86; 95% CI: 1.38-24.93) and no history of early rejection (aOR 3.96; 95% CI: 1.04-15.24) were independently associated with non-adherence. Lab non-adherence was significantly associated with medication non-adherence (P < .05), LAR (P = .02), and non-routine clinic visits (P = .03).

CONCLUSIONS

Systematic monitoring of lab adherence may help in identifying pediatric LT recipients at increased risk for excessive healthcare use and adverse outcomes possibly due to poor disease management.

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

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Hematocrit, blood volume, and surface area of dried blood spots - a quantitative model

The use of the dried blood spot (DBS) sampling technique has extended the scope of clinical research, particularly in children. The effects of different hematocrit levels (25-55%) and different blood volumes (7.5-30 μL) on the surface area of the blood spots were investigated using ImageJ® software. Variation in hematocrit levels between patients and inaccuracies in blood volumes applied to Guthrie cards can have a marked effect on analyte concentrations measured in DBS samples. The current study presents a validated model that links blood volume and hematocrit to the surface area of the blood spot. The final model showed that both factors affect the blood spot surface area, however, the positive effect of blood volume is higher than the negative effect of hematocrit. The measurement of surface area could be added as an additional quality control step in clinical studies that have adopted fixed volume DBS sampling for the quantification of the analytes. This approach can be used in estimating the hematocrit if this is not known for a patient or estimating the volume in spots that are visually different in size from the norm, i.e. technical error.

A multiple methods approach to determine adherence with prescribed mycophenolate in children with kidney transplant

AIMS

The aim of this study was, to use a multiple methods approach, including, for the first time, dried blood spot (DBS) sampling with population pharmacokinetic interpretation, to assess adherence to mycophenolate in children with kidney transplant. A second aim was to identify patient/parental factors that influenced adherence and to link adherence behaviour to clinical outcomes.

METHODS

A convenience sample of 33 children with kidney transplant (age ≤ 18 years) who had been prescribed mycophenolate for at least 3 months were recruited from participating outpatient clinics in the UK and Jordan. Medication adherence was determined via self-report questionnaires, medication refill data from dispensing records, and via mycophenolic acid concentrations in plasma and DBS samples obtained from children during a clinic visit.

RESULTS

Through triangulation of results from the different methodological approaches a total of 12 children (36.4%) were deemed to be nonadherent with their prescribed mycophenolate treatment. Logistic regression analysis indicated that nonadherence was significantly associated with the presence of mycophenolate side effects. Poor adherence was positively linked to measures of poor clinical outcomes (hospitalisation and the need for kidney biopsy).

CONCLUSIONS

Despite the imperative regarding medication adherence to help prevent organ rejection, a significant proportion of children are not fully adherent with their therapy. Side-effects appear to be an important factor leading to nonadherence. Measurement of mycophenolate in DBS samples, coupled with the use of population pharmacokinetics modelling, was a convenient direct approach to assessing adherence in children with kidney transplant and has the potential to be introduced into routine practice.