Therapeutic drug monitoring in oncology: International Association of Therapeutic Drug Monitoring and Clinical Toxicology consensus guidelines for imatinib therapy

Recent Advances in Therapeutic Drug Monitoring of Antineoplastic and Antimicrobial Agents in Children

Therapeutic drug monitoring (TDM) is used to optimize drug therapy by ensuring efficacy or preventing toxicity. For a limited number of cytotoxic antineoplastic drugs, for aminoglycoside antibiotics, and for vancomycin the use of TDM is common practice. In this article, we summarize recent advances and indications for the TDM of antineoplastic agents in children, focusing on protein kinase inhibitors and the cytotoxic drug fludarabine. We also summarize recent recommendations for antimicrobial TDM of beta-lactam antibiotics and vancomycin.

Therapeutic drug monitoring of imatinib in paediatric chronic myeloid leukaemia: Data from a real-world setting

Imatinib (IMA) therapy for paediatric chronic myeloid leukemia (pCML) requires age-dependent dose adjustments. Assessment of therapeutic drug monitoring (TDM) under 'real-world' conditions was performed. Collection of blood and TDM-relevant data, calculation of individual dosage exposure, measurement of plasma Cmin (IMA, Nor-IMA) by HPLC/MS-MS and recording of adverse event (AE). Two hundred and forty-six specimens from 66 patients were analysed. Individual median IMA dosage exposure was 253 mg/m2 (range: 128-504). Children <13 years received a median of 43 mg/m2 more than older patients (p < 0.0001). Median Cmin of IMA and Nor-IMA was 1017 ng/mL (range: 51-3976) and 269 ng/mL (range: 21-981), respectively, correlating significantly with the prescribed dose. At 5/246 visits, non-adherence was confirmed by very low IMA Cmin in 3/66 patients, all ≥13 years old. Correlation of IMA Cmin >1000 ng/mL with achieving OMR demonstrated in each 63% (N = 24/37, N = 27/43, respectively) patients at months 3 and 6. In the cohort with lower levels, only 23% and 50%, respectively, achieved these milestones. This difference was significant only at month 3. Of 66 patients, 30 reported 125 AEs with gastrointestinal and musculoskeletal as leading complaints. In 9.3% of AEs, the correlated IMA Cmin was ≥3000 ng/mL. TDM is a simple and rapid additional tool for managing pCML under 'real-world conditions'.

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.

Disease-Drug-Drug Interaction of Imatinib in COVID-19 ARDS: A Pooled Population Pharmacokinetic Analysis

Prior pharmacokinetic (PK) analysis revealed that increased alpha-1-acid glycoprotein (AAG) levels are associated with decreased imatinib unbound fraction in coronavirus disease 2019 (COVID-19) patients. This study aimed to investigate the PK of total and unbound concentrations of imatinib and the metabolite N-desmethyl imatinib in hospitalized patients with different severities of COVID-19, and to assess the impact of critical illness and the potential drug-drug interaction with IL-6R inhibitors on imatinib exposure. Imatinib, N-desmethyl imatinib, and AAG were quantified from collected plasma samples. The PK data was further combined with previous data from COVID-19 patients and chronic myelogenous leukemia/gastrointestinal stromal tumor (CML/GIST) patients who received imatinib. A population PK analysis was conducted using a standard sequential approach. Unbound fraction in COVID-19 patients admitted to the intensive care unit (ICU) and treated with IL-6R inhibitors was significantly elevated compared to CML/GIST patients (4.66% vs. 3.54% [1.08%-8.51%]; p < 0.001), despite twofold increased AAG levels. Our findings on total and unbound concentration show that cotreatment with IL-6R inhibitor can lead to changes in metabolism and protein binding, suggesting similar implications for other highly protein bound drugs. Consequently, total concentrations may not accurately reflect unbound target site concentrations.

LC-MS/MS method for quantification of 23 TKIs in Plasma: Assessing the relationship between anlotinib trough concentration and toxicities

OBJECTIVES

To develop a simple, rapid, and sensitive LC-MS/MS method for quantifying 23 tyrosine kinase inhibitors (TKIs) in plasma samples, and evaluate the relationship between the trough concentration of anlotinib(ANL) and its toxicities.

METHODS

The method was developed in Agilent 1290-6460 UHPLC-MS/MS system. This study prospectively enrolled 55 cancer patients undergoing ANL treatment. Plasma samples were collected at steady-state trough concentration and subsequently analyzed using the method. Patients were recorded for the occurrence of toxicities. Statistical analysis was performed to assess the association of the toxicities with ANL exposure level and patients' characteristics.

RESULTS

The LC-MS/MS method was developed and validated for all items required by pharmacopoeia. The results revealed a positive association between the trough concentration of ANL and the incidence of toxicities. The exposure level 17.655 ng/mL (AUC 0.82, p = 0.010) was identified as a predictive threshold value for grade ≥ 3 overall toxicities. In addition, lower platelet count (PLT count < 179 × 109 g/L) was significantly associated with higher occurrence of grade ≥ 3 toxicities (AUC 0.75, p = 0.049). A logistic model incorporating these two factors demonstrated improved diagnostic capacity for predicting ≥ 3 overall toxicities (AUC = 0.90, p = 0.001).

CONCLUSIONS

This study successfully developed and validated a simple, rapid, and sensitive LC-MS/MS method for quantifying 23 TKIs in plasma samples. Besides, this study found that both Ctrough of ANL and PLT count as independent predictors for ANL-induced ≥ 3 overall toxicities. Moreover, a logistic model including these two factors presents better prediction capacity for ≥ 3 overall toxicities.

Imatinib adherence prediction using machine learning approach in patients with gastrointestinal stromal tumor

BACKGROUND

Nonadherence to imatinib is common in patients with gastrointestinal stromal tumor (GIST), which is associated with poor prognosis and financial burden. The primary aim of this study was to investigate the adherence rate in patients with GIST and subsequently develop a model based on machine learning (ML) and deep learning (DL) techniques to identify the associated factors and predict the risk of imatinib nonadherence.

METHODS

All eligible patients completed four sections of questionnaires. After the data set was preprocessed, statistically significance variables were identified and further processed to modeling. Six ML and four DL algorithms were applied for modeling, including eXtreme gradient boosting, light gradient boosting machine (LGBM), categorical boosting, random forest, support vector machine, artificial neural network, multilayer perceptron, NaiveBayes, TabNet, and Wide&Deep. The optimal ML model was used to identify potential factors for predicting adherence.

RESULTS

A total of 397 GIST patients were recruited. Nonadherence was observed in 185 patients (53.4%). LGBM exhibited superior performance, achieving a mean f1_score of 0.65 and standard deviation of 0.12. The predominant indicators for nonadherent prediction of imatinib were cognitive functioning, whether to perform therapeutic drug monitoring (if_TDM), global health status score, social support, and gender.

CONCLUSIONS

This study represents the first real-world investigation using ML techniques to predict risk factors associated with imatinib nonadherence in patients with GIST. By highlighting the potential factors and identifying high-risk patients, the multidisciplinary medical team can devise targeted strategies to effectively address the daily challenges of treatment adherence.

Biopharmaceutical and pharmacokinetic attributes to drive nanoformulations of small molecule tyrosine kinase inhibitors

Buoyed by the discovery of small-molecule tyrosine kinase inhibitors (smTKIs), significant impact has been made in cancer chemotherapeutics. However, some of these agents still encounter off-target toxicities and suboptimal efficacies due to their inferior biopharmaceutical and/or pharmacokinetic properties. Almost all of these molecules exhibit significant inter- and intra-patient variations in plasma concentration-time profiles. Thus, therapeutic drug monitoring, dose adjustments and precision medicine are being contemplated by clinicians. Complex formulations or nanoformulation-based drug delivery systems offer promising approaches to provide drug encapsulation or spatiotemporal control over the release, overcoming the biopharmaceutical and pharmacokinetic limitations and improving the therapeutic outcomes. In this context, the present review comprehensively tabulates and critically analyzes all the relevant properties (T1/2, solubility, pKa, therapeutic index, IC50, metabolism etc.) of the approved smTKIs. A detailed appraisal is conducted on the advancements made in complex formulations of smTKIs, with a focus on strategies to enhance their pharmacokinetic profile, tumor targeting ability, and therapeutic efficacy. Various nanocarrier platforms, have been discussed, highlighting their unique features and potential applications in cancer therapy. Nanoformulations have been shown to improve area under the curve and peak plasma concentration, and reduce dosing frequency for several smTKIs in animal models. It is inferred that extensive efforts will be made in developing complex formulations of smTKIs in near future. There, the review concludes with key recommendations for the developing of smTKIs to facilitate early clinical translation.

Therapeutic Drug Monitoring of Imatinib: Is There a Rationale for Also Quantifying Its Active Metabolite?

INTRODUCTION

Therapeutic drug monitoring of imatinib is widely performed to individualize imatinib dosage. While N-desmethyl imatinib is an active metabolite of imatinib, its concentrations are not routinely determined.

METHODS

Imatinib and N-desmethyl imatinib trough plasma concentrations at steady-state were obtained from 295 patients with either chronic myeloid leukemia or gastrointestinal stromal tumor to see whether N-desmethyl imatinib provided additional information. Pharmacokinetic data were analyzed using a nonlinear mixed effect approach. Correlations between several pharmacokinetic metrics of drug exposure were evaluated.

RESULTS

The mean value of the N-desmethyl imatinib/imatinib ratio of trough concentrations was 0.31 with half of the values between 0.23 and 0.37. N-desmethyl imatinib and total (i.e., N-desmethyl imatinib plus imatinib) trough plasma concentrations or area under the curve values were closely correlated with imatinib values. The distribution of imatinib or total concentrations between patients requiring imatinib dosage adjustment, or not, was similar.

CONCLUSION

These results do not clearly support routine N-desmethyl monitoring since it does not provide additional information to imatinib data.

Increased plasma imatinib exposure and toxicity in chronically treated GIST patients with SARS-CoV-2 infection: a case series

Introduction

Inflammatory factors released during severe coronavirus disease-19 (COVID-19) caused by acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are known to influence drug exposure, but data on the effect of mild infection are few. Here we describe for the first time an increase in plasma imatinib and norimatinib concentrations observed in a series of 5 patients treated with imatinib for gastrointestinal stromal tumor (GIST) after mild COVID-19.

Methods

The patients were undergoing routine therapeutic drug monitoring (TDM) and pharmacogenetic (PGx) analyses of polymorphisms in genes involved in imatinib metabolism and transport (CYP3A4, CYP3A5, ABCB1, and ABCG2) when SARS-CoV-2 infection occurred. Imatinib and its active metabolite norimatinib concentrations were determined at Ctrough using a validated LC-MS/MS method. PGx analyses were performed by KASP genotyping assays on a Real-Time PCR system. All patients received imatinib 400 mg/day. Case 1 was prospectively monitored. Cases 2-5 were identified retrospectively.

Results

On average, imatinib Ctrough increased significantly by 70% during COVID-19, whereas norimatinib showed a 44% increase compared with pre-COVID-19 levels. Elevated plasma imatinib concentrations persisted up to 6 months after infection remission. In 3 cases, this increase reflected the occurrence or worsening of imatinib side effects.

Conclusion

This case-series highlights the clinical impact of SARS-CoV-2 infection on the management of patients with GIST treated with imatinib.

Simultaneous Determination of Ibrutinib, Dihydroxydiol Ibrutinib, and Zanubrutinib in Human Plasma by Liquid Chromatography-Mass Spectrometry/Mass Spectrometry

BACKGROUND

Ibrutinib and zanubrutinib are Bruton tyrosine kinase inhibitors used to treat mantle cell lymphoma, chronic lymphocytic leukemia, and small lymphocytic lymphoma. Dihydroxydiol ibrutinib (DHI) is an active metabolite of the drug. A liquid chromatography-tandem mass spectrometry method was developed to detect ibrutinib, DHI, and zanubrutinib in human plasma.

METHODS

The method involved a protein precipitation step, followed by chromatographic separation using a gradient of 10 mM ammonium acetate (containing 0.1% formic acid)-acetonitrile. Ibrutinib-d5 was used as an internal standard. Analytes were separated within 6.5 minutes. The optimized multiple reaction monitoring transitions of m/z 441.1 → 304.2, 475.2 → 304.2, 472.2 → 455.2, and 446.2 → 309.2 were selected to inspect ibrutinib, DHI, zanubrutinib, and the internal standards in positive ion mode.

RESULTS

The validated curve ranges included 0.200-800, 0.500-500, and 1.00-1000 ng/mL for ibrutinib, DHI, and zanubrutinib, respectively. The precisions of the lower limit of quantification of samples were below 15.5%, the precisions of the other level samples were below 11.4%, and the accuracies were between -8.6% and 8.4%. The matrix effect and extraction recovery of all compounds ranged between 97.6%-109.0% and 93.9%-105.2%, respectively. The selectivity, accuracy, precision, matrix effect, and extraction recovery results were acceptable according to international method validation guidelines.

CONCLUSIONS

A simple and rapid method was developed and validated in this study. This method was used to analyze plasma concentrations of ibrutinib and zanubrutinib in patients with mantle cell lymphoma, chronic lymphocytic leukemia/small lymphocytic lymphoma, or diffuse large B-cell lymphoma. The selected patients were aged between 44 and 74 years.

Simultaneous determination of three tyrosine kinase inhibitors and three triazoles in human plasma by LC-MS/MS: applications to therapeutic drug monitoring and drug-drug interaction studies

Tyrosine kinase inhibitors (TKIs) and triazole antifungals are the first-line drugs for treating chronic myeloid leukemia (CML) and fungal infections, respectively, but both suffer from large exposure differences and narrow therapeutic windows. Moreover, these two types of drugs are commonly used together in CML patients with fungal infections. Multiple studies and guidelines have suggested the importance of therapeutic drug monitoring (TDM) of TKIs and triazoles. Currently, methods for the simultaneous determination of both types of drugs are limited. We developed a simple, rapid, and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for simultaneous quantification of three commonly used TKIs (imatinib, dasatinib, and nilotinib) and three commonly used triazoles (voriconazole, itraconazole, and posaconazole) in human plasma. The analytes were eluted on a Welch XB-C18 analytical column (50 × 2.1 mm, 5 µm) at 0.7 mL/min, using a gradient elution of 10 mM ammonium formate (A) and methanol-acetonitrile-isopropanol (80:10:10, v/v/v) containing 0.2 % formic acid (B) with a total analysis time of 3.5 min. The calibration curves were linear over the range from 20 to 4000 ng/mL for imatinib and nilotinib, from 2 to 400 ng/mL for dasatinib, and from 50 to 10,000 ng/mL for voriconazole, itraconazole, and posaconazole. Selectivity, accuracy, precision, recovery, matrix effect, and stability all met the validation requirements. The method was successfully used for TDM in CML patients who co-treated with both TKIs and triazoles. Drug-drug interaction analysis between TKIs and triazoles showed that a significant positive correlation was observed between imatinib and voriconazole, as well as dasatinib and voriconazole. Therefore, this method can be well applied in clinical TDM for patients receiving TKIs, triazoles, or both simultaneously.

Therapeutic drug monitoring in anticancer agents: perspectives of Australian medical oncologists

BACKGROUND

In the development of anticancer agents for solid tumours, body surface area continues to be used to personalise dosing despite minimal evidence for its use over other dosing strategies. With the development of tyrosine kinase inhibitors and other oral targeted anticancer agents, dosing using therapeutic drug monitoring (TDM) is now utilised in many health systems but has had limited uptake in Australia.

AIM

To determine attitudes and barriers to the implementation of TDM among Australian oncologists.

METHODS

A comprehensive questionnaire was developed by the Dutch Pharmacology Oncology Group from semistructured interviews of stakeholders. Seventy-nine questions across seven domains were developed with three free-text responses. This was rationalised to 17 questions with three free-text responses for Australian medical oncologists who identified limited experience with TDM.

RESULTS

Fifty-seven responses were received, with 49 clinicians (86%) identifying limited experience of performing TDM in daily practice. Clinicians were positive (62-91% agree/strongly agree across seven questions) about the advantages of TDM. There was a mixed response for cost-effectiveness and scientific evidence being a barrier to implementation, but strong agreement that prospective studies were needed (75% agreed or strongly agreed); that national treatment guidelines would enable practice (80%) and that a 'pharmacology of oncolytics' education programme would be useful (96%) to provide knowledge for dose individualisation.

CONCLUSION

Despite the limited experience of TDM in oncology in Australia, medical oncologists appear positive about the potential benefit to their patients. We have identified three barriers to implementation that could be targeted for increased adoption of TDM in oncology in Australia.

Comparable efficacy and safety of generic and branded imatinib for patients with chronic myeloid leukemia in China

Background

Generics imatinib became an alternative treatment option for chronic myeloid leukemia (CML) patients in China. However, clinicians and patients alike harbor concerns regarding the long-term safety of generic imatinib.

Objectives

Patients with chronic phase CML receiving frontline imatinib treatment.

Design

A retrospective study was used to evaluate the blood concentration, effectiveness, and safety of generic in 170 CML patients.

Methods

Imatinib plasma concentrations were detected by high-performance liquid chromatography-tandem mass spectrometry.

Results

Among the 170 patients, 73 (42.9%) patients treated with branded imatinib as first-line therapy, while 22 (12.9%) switched to generic imatinib during treatment due to economic considerations. No significant differences in trough concentrations between branded and generic imatinib (1549.9 ± 648.8 ng/mL vs 1479.0 ± 507.0 ng/mL; p = 0.95). During the 2-year follow-up, there were no significant differences in molecular response rates (major molecular response (MMR): 33.3% vs 37.0%; deep molecular response: 56.9% vs 42.9%, p = 0.17) between the branded and generic imatinib. Both groups showed similar rates of switching to second-generation tyrosine kinase inhibitor (11.8% vs 15.1%, p = 0.56). Furthermore, there were no significant differences in event-free survival or failure-free survival between branded and generic imatinib. Twenty-two (12.9%) switched to generic imatinib during treatment, 68.2% maintained their level of response, 27.3% improved, and only one patient (4.5%) lost MMR. There were no significant differences in the incidence of various adverse events.

Conclusion

Generic imatinib are equally effective and safe compared to branded molecules, both for newly diagnosed patients and those who switch from branded.

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.

Closed-loop automated drug infusion regulator: A clinically translatable, closed-loop drug delivery system for personalized drug dosing

BACKGROUND

Dosing of chemotherapies is often calculated according to the weight and/or height of the patient or equations derived from these, such as body surface area (BSA). Such calculations fail to capture intra- and interindividual pharmacokinetic variation, which can lead to order of magnitude variations in systemic chemotherapy levels and thus under- or overdosing of patients.

METHODS

We designed and developed a closed-loop drug delivery system that can dynamically adjust its infusion rate to the patient to reach and maintain the drug's target concentration, regardless of a patient's pharmacokinetics (PK).

FINDINGS

We demonstrate that closed-loop automated drug infusion regulator (CLAUDIA) can control the concentration of 5-fluorouracil (5-FU) in rabbits according to a range of concentration-time profiles (which could be useful in chronomodulated chemotherapy) and over a range of PK conditions that mimic the PK variability observed clinically. In one set of experiments, BSA-based dosing resulted in a concentration 7 times above the target range, while CLAUDIA keeps the concentration of 5-FU in or near the targeted range. Further, we demonstrate that CLAUDIA is cost effective compared to BSA-based dosing.

CONCLUSIONS

We anticipate that CLAUDIA could be rapidly translated to the clinic to enable physicians to control the plasma concentration of chemotherapy in their patients.

FUNDING

This work was supported by MIT's Karl van Tassel (1925) Career Development Professorship and Department of Mechanical Engineering and the Bridge Project, a partnership between the Koch Institute for Integrative Cancer Research at MIT and the Dana-Farber/Harvard Cancer Center.

Therapeutic drug monitoring guidelines in oncology: what do we know and how to move forward? Insights from a systematic review

Background

Compared with anti-infective drugs, immunosuppressants and other fields, the application of therapeutic drug monitoring (TDM) in oncology is somewhat limited.

Objective

We aimed to provide a comprehensive understanding of TDM guidelines for antineoplastic drugs and to promote the development of individualized drug therapy in oncology.

Design

This study type is a systematic review.

Data sources and methods

This study was performed and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement. Databases including PubMed, Embase, the official websites of TDM-related associations and Chinese databases were comprehensively searched up to March 2023. Two investigators independently screened the literature and extracted data. The methodological and reporting quality was evaluated using the Appraisal of Guidelines for Research and Evaluation II (AGREE II) and the Reporting Items for Practice Guidelines in Healthcare (RIGHT), respectively. Recommendations and quality evaluation results were presented by visual plots. This study was registered in PROSPERO (No. CRD42022325661).

Results

A total of eight studies were included, with publication years ranging from 2014 to 2022. From the perspective of guideline development, two guidelines were developed using evidence-based methods. Among the included guidelines, four guidelines were for cytotoxic antineoplastic drugs, three for small molecule kinase inhibitors, and one for antineoplastic biosimilars. Currently available guidelines and clinical practice provided recommendations of individualized medication in oncology based on TDM, as well as influencing factors. With regard to methodological quality based on AGREE II, the average overall quality score was 55.21%. As for the reporting quality by RIGHT evaluation, the average reporting rate was 53.57%.

Conclusion

From the perspective of current guidelines, TDM in oncology is now being expanded from cytotoxic antineoplastic drugs to newer targeted treatments. Whereas, the types of antineoplastic drugs involved are still small, and there is still room for quality improvement. Furthermore, the reflected gaps warrant future studies into the exposure-response relationships and population pharmacokinetics models.

Paclitaxel therapeutic drug monitoring - International association of therapeutic drug monitoring and clinical toxicology recommendations

Paclitaxel, one of the most frequently used anticancer drugs, is dosed by body surface area, which leads to substantial inter-individual variability in systemic drug exposure. We evaluated clinical evidence regarding the scientific rationale and clinical benefit of individualized paclitaxel dosing based on measured systemic concentrations, known as therapeutic drug monitoring (TDM). In retrospective studies, higher systemic exposure is associated with greater toxicity and efficacy of paclitaxel treatment across several disease types and dosing regimens. In prospective trials, TDM reduces variability in systemic exposure, and has been demonstrated to reduce toxicity while retaining treatment efficacy for 3-weekly dosing in patients with advanced non-small cell lung cancer. Despite the demonstrated benefits of paclitaxel TDM, clinical adoption has been limited due to the challenges with sample collection and analysis. Based on our review, we strongly recommend TDM for patients receiving every 3-week paclitaxel in combination with a platinum agent for advanced NSCLC, due to the prospectively demonstrated clinical benefits, and find moderate evidence to recommend TDM for paclitaxel 3-hour infusions for other tumor types and preliminary evidence suggesting potential usefulness for paclitaxel administered by 1-hour infusions.

Therapeutic drug monitoring of imatinib - how far are we in the leukemia setting?

INTRODUCTION

Tyrosine kinase inhibitors (TKIs) have revolutionized survival rates of chronic myeloid leukemia (CML) and Philadelphia chromosome positive (Ph+) acute lymphoblastic leukemia (ALL) and replaced hematopoietic stem cell transplantation (hSCT) as the key treatment option for these patients. More recently, the so-called Philadelphia chromosome-like (Ph-like) ALL has similarly benefitted from TKIs. However, many patients shift from the first generation TKI, imatinib, due to treatment-related toxicities or lack of treatment efficacy. A more personalized approach to TKI treatment could counteract these challenges and potentially be more cost-effective. Therapeutic drug monitoring (TDM) has led to higher response rates and less treatment-related toxicity in adult CML but is rarely used in ALL or in childhood CML.

AREAS COVERED

This review summarizes different antileukemic treatment indications for TKIs with focus on imatinib and its pharmacokinetic/-dynamic properties as well as opportunities and pitfalls of TDM for imatinib treatment in relation to pharmacogenetics and co-medication for pediatric and adult Ph+/Ph-like leukemias.

EXPERT OPINION

TDM of imatinib adds value to standard monitoring of ABL-class leukemia by uncovering non-adherence and potentially mitigating adverse effects. Clinically implementable pharmacokinetic/-dynamic models adjusted for relevant pharmacogenetics could improve individual dosing. Prospective trials of TDM-based treatments, including both children and adults, are needed.

Clinical pharmacokinetics and drug-drug interactions of tyrosine-kinase inhibitors in chronic myeloid leukemia: A clinical perspective

In the past decade, numerous tyrosine kinase inhibitors (TKIs) have been introduced in the treatment of chronic myeloid leukemia. Given the significant interpatient variability in TKIs pharmacokinetics, potential drug-drug interactions (DDIs) can greatly impact patient therapy. This review aims to discuss the pharmacokinetic characteristics of TKIs, specifically focusing on their absorption, distribution, metabolism, and excretion profiles. Additionally, it provides a comprehensive overview of the utilization of TKIs in special populations such as the elderly, children, and patients with liver or kidney dysfunction. We also highlight known or suspected DDIs between TKIs and other drugs, highlighting various clinically relevant interactions. Moreover, specific recommendations are provided to guide haemato-oncologists, oncologists, and clinical pharmacists in managing DDIs during TKI treatment in daily clinical practice.

The use of therapeutic drug monitoring to highlight an over-looked drug-drug interaction leading to imatinib treatment failure

BACKGROUND

Chronic oral anticancer therapies, are increasingly prescribed and present new challenges including the enhanced risk of overlooked drug-drug interactions (DDIs). Lengthy treatments and patients' management by different professionals can lead to serious prescribing errors that therapeutic drug monitoring (TDM) can help identifying thus allowing a more effective and safer treatment of patients with polypharmacy.

OBJECTIVES

This report aims to exemplify how an intensified pharmacological approach could help in the clinical monitoring of patients on chronic treatments.

METHODS

A patient with gastrointestinal stromal tumor was referred to our clinical pharmacology service due to tumor progression while on imatinib therapy. The investigation was based on TDM, pharmacogenetics, DDI evaluation and Circulating tumor DNA (ctDNA) analysis. The patient underwent repeated blood samplings to measure imatinib and norimatinib plasma concentrations through a validated LC-MS/MS method. Polymorphisms affecting genes involved in imatinib metabolism and transport were investigated using SNPline PCR Genotyping System. Drug-drug interactions were evaluated though Lexicomp. ctDNA analysis was performed on MiSeq platform.

RESULTS

TDM analysis revealed that the patient was underexposed to imatinib (Cmin = 406 ng/mL; target Cmin = 1100 ng/mL). Subsequent DDI analysis highlighted a dangerous interaction with carbamazepine, via CYP3A4 and P-gp strong induction, omitted at the time of imatinib treatment start. No relevant pharmacogenetic variants were identified and appropriate compliance to treatment was ascertained. ctDNA monitoring was performed to assess potential tumor-related resistance to imatinib. Carbamazepine was cautiously switched to a non-interacting antiepileptic drug, restoting IMA plasma concentration (i.e. Cmin = 4298 ng/mL). The progression of the disease, which in turn led to the patient's death, was also witnessed by an increasing fraction of ctDNA in plasma.

CONCLUSION

The active pharmacological monitoring allowed the identification of a dangerous previously over-looked DDI leading to IMA under-exposure. The switch to a different antiepileptic treatment, reversed the effect of DDI, restoring therapeutic IMA plasmatic concentrations.

Personalized Minimal Effective Concentration Therapy

It has been recognized for literally centuries that patients should be given only the amount of medication necessary to treat disease(s) or relieve symptoms. It is also well known that this amount can vary greatly between patients or even over time in the same patient. The ability to identify this amount, that is, to "personalize" dosing, requires a reliable measure of a patient's response to treatment. The development of analytical methods for the accurate measurement of pharmacologically meaningful drug concentrations in physiologic fluids, combined with mathematical methods for reliable prediction of how dosing changes affect these concentrations, has led to the development of therapeutic drug management (TDM) for more effective individualization of dosing. Using TDM, clinicians modify dosing to achieve concentrations or exposures (ie, AUC) found to be effective in patients with similar clinical attributes and conditions. These concentrations, called therapeutic (or target) concentrations or exposure ranges (TRs), are specific to both disease/condition and patient population. TDM is routinely used by many clinicians to adjust dosing of a wide range of medications for maximal efficacy and limited toxicity, thereby improving clinical outcomes. Failure to properly perform TDM or to appreciate the limitations of TDM have, however, contributed to the delayed acceptance of TDM by clinicians. This Commentary briefly discusses the limitations and the benefits of TR-guided TDM, and then discusses immunosuppressant drugs and anticancer medications as examples of drugs that require clinicians to change their prescribing practices from giving all patients the same or maximal tolerated doses, to instead adjusting individual doses to achieve minimal effective concentrations identified using circulating tumor- or graft-derived DNA or copy number instability rather than published TRs.

Therapeutic drug monitoring and pharmacogenetics to tune imatinib exposure in gastrointestinal stromal tumor patients: hurdles and perspectives for clinical implementation

Tweetable abstract Present evidence supports the use of intensified pharmacologic monitoring of #imatinib including #TherapeuticDrugMonitoring and #PGx to improve outcomes in patients with GI stromal tumor. Future studies need to address emerging questions to facilitate implementation in clinics.

Population pharmacokinetics and pharmacogenetics analyses of imatinib in Chinese patients with chronic myeloid leukemia in a real-world situation

BACKGROUND

Imatinib is presently the first-line choice for the treatment of chronic myeloid leukemia. However, there are limited real-world data on Chinese patients to support individualized medicine. This work aims to characterize population pharmacokinetics in Chinese patients with chronic myeloid leukemia, investigate the effects of several covariates on imatinib exposure, and provide support for personalized medicine and dose reduction.

METHODS

A total of 230 patients with chronic myeloid leukemia were enrolled, and 424 steady-state concentration measurements were taken to perform the population pharmacokinetic analysis and Monte Carlo simulations with Phoenix NLME software. The effects of the demographic, biological, and pharmacogenetic (ten SNP corresponding to CYP3A4, CYP3A5, ABCB1, ABCG2, SCL22A1 and POR) covariates on clearance were evaluated.

RESULTS

A one-compartmental model best-described imatinib pharmacokinetics. The hemoglobin and the estimated glomerular filtration rate (< 85 mL⋅min-1⋅1.73 m2) were associated with imatinib clearance. The genetic polymorphisms related to pharmacokinetics were not found to have a significant effect on the clearance of imatinib. The final model estimates of parameters are: ka (h-1) = 0.329; Vd/F (L) = 270; CL/F (L⋅h-1) = 7.60.

CONCLUSIONS

Key covariates in the study population accounting for variability in imatinib exposure are hemoglobin and the estimated glomerular filtration rate. There is some need for caution when treating patients with moderate-to-severe renal impairment and significant hemoglobin changes.

Therapeutic Drug Monitoring of Kinase Inhibitors in Oncology

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

Novel Approaches to Characterize Individual Drug Metabolism and Advance Precision Medicine

Interindividual variability in drug metabolism can significantly affect drug concentrations in the body and subsequent drug response. Understanding an individual's drug metabolism capacity is important for predicting drug exposure and developing precision medicine strategies. The goal of precision medicine is to individualize drug treatment for patients to maximize efficacy and minimize drug toxicity. While advances in pharmacogenomics have improved our understanding of how genetic variations in drug-metabolizing enzymes (DMEs) affect drug response, nongenetic factors are also known to influence drug metabolism phenotypes. This minireview discusses approaches beyond pharmacogenetic testing to phenotype DMEs-particularly the cytochrome P450 enzymes-in clinical settings. Several phenotyping approaches have been proposed: traditional approaches include phenotyping with exogenous probe substrates and the use of endogenous biomarkers; newer approaches include evaluating circulating noncoding RNAs and liquid biopsy-derived markers relevant to DME expression and function. The goals of this minireview are to 1) provide a high-level overview of traditional and novel approaches to phenotype individual drug metabolism capacity, 2) describe how these approaches are being applied or can be applied to pharmacokinetic studies, and 3) discuss perspectives on future opportunities to advance precision medicine in diverse populations. SIGNIFICANCE STATEMENT: This minireview provides an overview of recent advances in approaches to characterize individual drug metabolism phenotypes in clinical settings. It highlights the integration of existing pharmacokinetic biomarkers with novel approaches; also discussed are current challenges and existing knowledge gaps. The article concludes with perspectives on the future deployment of a liquid biopsy-informed physiologically based pharmacokinetic strategy for patient characterization and precision dosing.

Pharmacokinetics of Four Tyrosine Kinase Inhibitors in Adult and Paediatric Chronic Myeloid Leukaemia Patients

Tyrosine kinase inhibitors work by blocking the tyrosine kinases responsible for the dysregulation of intracellular signalling pathways in tumour cells. This study looked at the impact of age and sex on the levels of imatinib, dasatinib, nilotinib, and ponatinib in plasma and cerebrospinal fluid samples of patients with chronic myeloid leukaemia. Imatinib and dasatinib were used to treat the majority of the enrolled patients, and most of them were paediatrics. A total of 82.4% of the patients were men; however, sex-related differences in the drugs' pharmacokinetics were not found. Age and imatinib plasma concentration were found to be inversely correlated. The dasatinib concentrations in plasma were found to be substantially lower than those found in cerebrospinal fluid, particularly in paediatrics. Analysing the obtained data, we can state that therapeutic drug monitoring is a useful method for adjusting a patient's treatment schedule that depends on drug concentrations in biological fluids. The use of therapeutic drug monitoring in conjunction with tyrosine kinase inhibitors for the treatment of chronic myeloid leukaemia is supported by a number of sources of evidence. As a result, as the research develops, the tyrosine kinase inhibitor therapeutic drug monitoring classification needs to be refined in terms of factors like sex and age.

Status and Quality of Guidelines for Therapeutic Drug Monitoring Based on AGREE II Instrument

BACKGROUND

With the progress of therapeutic drug monitoring (TDM) technology and the development of evidence-based medicine, many guidelines were developed and implemented in recent decades.

OBJECTIVE

The aim was to evaluate the current status of TDM guidelines and provide suggestions for their development and updates based on Appraisal of Guidelines for Research and Evaluation (AGREE) II.

METHODS

The TDM guidelines were systematically searched for among databases including PubMed, Embase, China National Knowledge Infrastructure, Wanfang Data, and the Chinese biomedical literature service system and the official websites of TDM-related associations. The search period was from inception to 6 April 2023. Four researchers independently screened the literature and extracted data. Any disagreement was discussed and reconciled by another researcher. The quality of guidelines was assessed using the AGREE II instrument.

RESULTS

A total of 92 guidelines were included, including 57 technical guidelines, three management guidelines, and 32 comprehensive guidelines. The number of TDM guidelines has gradually increased since 1979. The United States published the most guidelines (20 guidelines), followed by China (15 guidelines) and the United Kingdom (ten guidelines), and 23 guidelines were developed by international organizations. Most guidelines are aimed at adult patients only, while 28 guidelines include special populations. With respect to formulation methods, there are 23 evidence-based guidelines. As for quality evaluation results based on AGREE II, comprehensive guidelines scored higher (58.16%) than technical guidelines (51.36%) and administrative guidelines (50.00%).

CONCLUSION

The number of TDM guidelines, especially technical and comprehensive ones, has significantly increased in recent years. Most guidelines are confronted with the problems of unclear methodology and low quality of evidence according to AGREE II. More evidence-based research on TDM and high-quality guideline development is recommended to promote individualized therapy.

Dose optimization strategy of the tyrosine kinase inhibitors imatinib, dasatinib, and nilotinib for chronic myeloid leukemia: From clinical trials to real-life settings

With the advent of tyrosine kinase inhibitors (TKIs), the treatment prospects of chronic myeloid leukemia (CML) have changed markedly. This innovation can lengthen the long-term survival of patients suffering from CML. However, long-term exposure to TKIs is accompanied by various adverse events (AEs). The latter affect the quality of life and compliance of patients with CML, and may lead to serious disease progression (and even death). Recently, increasing numbers of patients with CML have begun to pursue a dose optimization strategy. Dose optimization may be considered at all stages of the entire treatment, which includes dose reduction and discontinuation of TKIs therapy. In general, reduction of the TKI dose is considered to be an important measure to reduce AEs and improve quality of life on the premise of maintaining molecular responses. Furthermore, discontinuation of TKIs therapy has been demonstrated to be feasible and safe for about half of patients with a stable optimal response and a longer duration of TKI treatment. This review focuses mainly on the latest research of dose optimization of imatinib, dasatinib, and nilotinib in CML clinical trials and real-life settings. We consider dose reduction in newly diagnosed patients, or in optimal response, or for improving AEs, either as a prelude to treatment-free remission (TFR) or as maintenance therapy in those patients unable to discontinue TKIs therapy. In addition, we also focus on discontinuation of TKIs therapy and second attempts to achieve TFR.

Pharmacogenetics and Adverse Events in the Use of Fluoropyrimidine in a Cohort of Cancer Patients on Standard of Care Treatment in Zimbabwe

Fluoropyrimidines are commonly used in the treatment of colorectal cancer. They are, however, associated with adverse events (AEs), of which gastrointestinal, myelosuppression and palmar-plantar erythrodysesthesia are the most common. Clinical guidelines are used for fluoropyrimidine dosing based on dihydropyrimidine dehydrogenase (DPYD) genetic polymorphism and have been shown to reduce these AEs in patients of European ancestry. This study aimed to evaluate, for the first time, the clinical applicability of these guidelines in a cohort of cancer patients on fluoropyrimidine standard of care treatment in Zimbabwe. DNA was extracted from whole blood and used for DPYD genotyping. Adverse events were monitored for six months using the Common Terminology Criteria for AEs (CTCAE) v.5.0. None of the 150 genotyped patients was a carrier of any of the pathogenic variants (DPYD*2A, DPYD*13, rs67376798, or rs75017182). However, severe AEs were high (36%) compared to those reported in the literature from other populations. There was a statistically significant association between BSA (p = 0.0074) and BMI (p = 0.0001) with severe global AEs. This study has shown the absence of the currently known actionable DPYD variants in the Zimbabwean cancer patient cohort. Therefore, the current pathogenic variants in the guidelines might not be feasible for all populations hence the call for modification of the current DPYD guidelines to include minority populations for the benefit of all diverse patients.

From Personalized to Precision Medicine in Oncology: A Model-Based Dosing Approach to Optimize Achievement of Imatinib Target Exposure

Imatinib is a targeted cancer therapy that has significantly improved the care of patients with chronic myeloid leukemia (CML) and gastrointestinal stromal tumor (GIST). However, it has been shown that the recommended dosages of imatinib are associated with trough plasma concentration (Cmin) lower than the target value in many patients. The aims of this study were to design a novel model-based dosing approach for imatinib and to compare the performance of this method with that of other dosing methods. Three target interval dosing (TID) methods were developed based on a previously published PK model to optimize the achievement of a target Cmin interval or minimize underexposure. We compared the performance of those methods to that of traditional model-based target concentration dosing (TCD) as well as fixed-dose regimen using simulated patients (n = 800) as well as real patients’ data (n = 85). Both TID and TCD model-based approaches were effective with about 65% of Cmin achieving the target imatinib Cmin interval of 1000–2000 ng/mL in 800 simulated patients and more than 75% using real data. The TID approach could also minimize underexposure. The standard 400 mg/24 h dosage of imatinib was associated with only 29% and 16.5% of target attainment in simulated and real conditions, respectively. Some other fixed-dose regimens performed better but could not minimize over- or underexposure. Model-based, goal-oriented methods can improve initial dosing of imatinib. Combined with subsequent TDM, these approaches are a rational basis for precision dosing of imatinib and other drugs with exposure–response relationships in oncology.

Proactive therapeutic drug monitoring of vincristine in pediatric and adult cancer patients: current supporting evidence and future efforts

Vincristine (VCR), an effective antitumor drug, has been utilized in several polytherapy regimens for acute lymphoblastic leukemia, neuroblastoma and rhabdomyosarcoma. However, clinical evidence shows that the metabolism of VCR varies greatly among patients. The traditional based body surface area (BSA) administration method is prone to insufficient exposure to VCR or severe VCR-induced peripheral neurotoxicity (VIPN). Therefore, reliable strategies are urgently needed to improve efficacy and reduce VIPN. Due to the unpredictable pharmacokinetic changes of VCR, therapeutic drug monitoring (TDM) may help to ensure its efficacy and to manage VIPN. At present, there is a lot of supporting evidence for the suitability of applying TDM to VCR therapy. Based on the consensus guidelines drafted by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT), this review aimed to summarize various available data to evaluate the potential utility of VCR TDM for cancer patients. Of note, valuable evidence has accumulated on pharmacokinetics variability, pharmacodynamics, drug exposure-clinical response relationship, biomarkers for VIPN prediction, and assays for VCR monitoring. However, there are still many relevant clinical pharmacological questions that cannot yet be answered merely based on insufficient evidence. Currently, we cannot recommend a therapeutic exposure range and cannot yet provide a dose-adaptation strategy for clinicians and patients. In areas where the evidence is not yet sufficient, more research is needed in the future. The precision medicine of VCR cannot rely on TDM alone and needs to consider the clinical, environmental, genetic background and patient-specific factors as a whole.

The Application of Virtual Therapeutic Drug Monitoring to Assess the Pharmacokinetics of Imatinib in a Chinese Cancer Population Group

PURPOSE

Imatinib is used in gastrointestinal stromal tumours (GIST) and chronic myeloid leukaemia (CML). Oncology patients demonstrate altered physiology compared to healthy adults, e.g. reduced haematocrit, increased α-1 acid glycoprotein, decreased albumin and reduced glomerular filtration rate (GFR), which may influence imatinib pharmacokinetics. Given that Chinese cancer patients often report raised imatinib plasma concentrations and wider inter-individual variability reported in trough concentration when compared to Caucasian cancer patients, therapeutic drug monitoring (TDM) has been advocated.

METHOD

This study utilised a previously validated a Chinese cancer population and assessed the impact of imatinib virtual-TDM in Chinese and Caucasian cancer populations across a dosing range from 200-800 mg daily.

RESULTS

Staged dose titration to 800 mg daily, resulted in recapitulation to within the target therapeutic range for 50 % (Chinese) and 42.1% (Caucasian) subjects possessing plasma concentration < 550 ng/mL when dosed at 400 mg daily. For subjects with plasma concentrations >1500 ng/mL when dosed at 400 mg daily, a dose reduction to 200 mg once daily was able to recover 67 % (Chinese) and 87.4 % (Caucasian) patients to the target therapeutic range.

CONCLUSION

Virtual TDM highlights the benefit of pharmacokinetic modelling to optimising treatments in challenging oncology population groups.

Therapeutic Monitoring of Orally Administered, Small-Molecule Anticancer Medications with Tumor-Specific Cellular Protein Targets in Peripheral Fluid Spaces-A Review

Orally administered, small-molecule anticancer drugs with tumor-specific cellular protein targets (OACD) have revolutionized oncological pharmacotherapy. Nevertheless, the differences in exposure to these drugs in the systemic circulation and extravascular fluid compartments have led to several cases of therapeutic failure, in addition to posing unknown risks of toxicity. The therapeutic drug monitoring (TDM) of OACDs in therapeutically relevant peripheral fluid compartments is therefore essential. In this work, the available knowledge regarding exposure to OACD concentrations in these fluid spaces is summarized. A review of the literature was conducted by searching Embase, PubMed, and Web of Science for clinical research articles and case reports published between 10 May 2001 and 31 August 2022. Results show that, to date, penetration into cerebrospinal fluid has been studied especially intensively, in addition to breast milk, leukocytes, peripheral blood mononuclear cells, peritoneal fluid, pleural fluid, saliva and semen. The typical clinical indications of peripheral fluid TDM of OACDs were (1) primary malignancy, (2) secondary malignancy, (3) mental disorder, and (4) the assessment of toxicity. Liquid chromatography-tandem mass spectrometry was most commonly applied for analysis. The TDM of OACDs in therapeutically relevant peripheral fluid spaces is often indispensable for efficient and safe treatments.

Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors in the Treatment of Advanced Renal Cancer

Seven tyrosine kinase inhibitor compounds with anti-angiogenic properties remain key drugs to treat advanced renal cell carcinoma. There is a strong rationale to develop therapeutic drug monitoring for these drugs. General considerations of such monitoring of the several groups of anticancer drugs are given, with a focus on oral therapy. Pharmacokinetics and the factors of inter- and intraindividual variabilities of these tyrosine kinase inhibitors are described together with an exhaustive presentation of their pharmacokinetic/pharmacodynamic relationships. The latter was observed in studies where every patient was treated with the same dose, and the results of several prospective studies based on dose individualization support the practice of increasing individual dosage in case of low observed plasma drug concentrations. Finally, the benefits and limits of therapeutic drug monitoring as a routine practice are discussed.

Therapeutic Drug Monitoring of Protein Kinase Inhibitors in the Treatment of Non-small Cell Lung Cancer

Targeted therapy with protein kinase inhibitors (PKIs) represents one of the important treatment options for non-small cell lung cancer (NSCLC). It has contributed to improve patients' survival and quality of life significantly. These anticancer drugs are administrated orally in flat-fixed doses despite the well-known large interpatient pharmacokinetic variability and the possible need for dose individualization. To optimize and individualize dosing of PKIs, and thereby increasing the effectiveness and safety of the treatment, therapeutic drug monitoring (TDM) is the most frequently mentioned method. Unlike other areas of medicine, TDM has been rather exceptional in oncological practise since there is a little evidence or no data for concentration-effect relationships of PKIs. Therefore, the aim of this review is to summarize the pharmacokinetic characteristics of PKIs and provide the evidence supporting the use of TDM for personalised treatment of patients with NSCLC.

All Optimal Dosing Roads Lead to Therapeutic Drug Monitoring-Why Take the Slow Lane

This Viewpoint discusses therapeutic drug monitoring as a necessary treatment paradigm and the need for regulatory agencies to provide the conditions to make it happen.

Imatinib dose optimization based on therapeutic drug monitoring in Chinese patients with chronic-phase chronic myeloid leukemia

BACKGROUND

Imatinib treatment often produces various adverse reactions in patients with chronic myeloid leukemia (CML), and increasing patients are pursuing dose optimization. In this study, the authors aimed to explore imatinib dose optimization based on therapeutic drug monitoring (TDM) in CML patients.

METHODS

The relationship between imatinib concentration and clinical response and adverse reactions was evaluated, then the dose-reduction data in 110 Chinese CML patients was also explored.

RESULTS

Patients with a major molecular response (MMR) had higher imatinib plasma concentration compared with those not achieving MMR (1473.70 ± 419.13 vs. 985.8 ± 213.32 ng/ml) when receiving 400 mg daily. Imatinib concentration >1000 ng/ml predicted improved event-free survival and failure-free survival. In addition, imatinib concentration was significantly correlated with leukopenia or neutropenia, diarrhea, edema, and rash. Patients receiving imatinib concentration >1685 ng/ml were more susceptible to diarrhea and those with levels >1575 ng/ml were more susceptible to periorbital and limb edema. Thirty-nine (35.5%) patients underwent low-dose therapy and seven (6.4%) patients received discontinuation therapy. Patients with a higher imatinib concentration were more likely to maintain MMR or deep molecular response after dose reduction. No significant difference in molecular relapse-free survival rate was observed between the low-dose and standard-dose groups over 1 year and 2 years. Furthermore, most adverse reactions significantly improved after dose reduction.

CONCLUSIONS

Imatinib concentration was closely associated with clinical response and adverse reactions, suggesting that dose optimization based on TDM might achieve beneficial clinical outcomes. Dose reduction based on TDM is feasible and safe for patients exhibiting optimal response, which could improve adverse reactions.

How Surface-Enhanced Raman Spectroscopy Could Contribute to Medical Diagnoses

In the last decade, there has been a rapid increase in the number of surface-enhanced Raman scattering (SERS) spectroscopy applications in medical research. In this article we review some recent, and in our opinion, most interesting and promising applications of SERS spectroscopy in medical diagnostics, including those that permit multiplexing within the range important for clinical samples. We focus on the SERS-based detection of markers of various diseases (or those whose presence significantly increases the chance of developing a given disease), and on drug monitoring. We present selected examples of the SERS detection of particular fragments of DNA or RNA, or of bacteria, viruses, and disease-related proteins. We also describe a very promising and elegant ‘lab-on-chip’ approach used to carry out practical SERS measurements via a pad whose action is similar to that of a pregnancy test. The fundamental theoretical background of SERS spectroscopy, which should allow a better understanding of the operation of the sensors described, is also briefly outlined. We hope that this review article will be useful for researchers planning to enter this fascinating field.

Therapeutic Drug Monitoring of Tyrosine Kinase Inhibitors Using Dried Blood Microsamples

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