Therapeutic Drug Monitoring of Targeted Anticancer Protein Kinase Inhibitors in Routine Clinical Use: A Critical Review

BACKGROUND

Therapeutic response to oral targeted anticancer protein kinase inhibitors (PKIs) varies widely between patients, with insufficient efficacy of some of them and unacceptable adverse reactions of others. There are several possible causes for this heterogeneity, such as pharmacokinetic (PK) variability affecting blood concentrations, fluctuating medication adherence, and constitutional or acquired drug resistance of cancer cells. The appropriate management of oncology patients with PKI treatments thus requires concerted efforts to optimize the utilization of these drug agents, which have probably not yet revealed their full potential.

METHODS

An extensive literature review was performed on MEDLINE on the PK, pharmacodynamics, and therapeutic drug monitoring (TDM) of PKIs (up to April 2019).

RESULTS

This review provides the criteria for determining PKIs suitable candidates for TDM (eg, availability of analytical methods, observational PK studies, PK-pharmacodynamics relationship analysis, and randomized controlled studies). It reviews the major characteristics and limitations of PKIs, the expected benefits of TDM for cancer patients receiving them, and the prerequisites for the appropriate utilization of TDM. Finally, it discusses various important practical aspects and pitfalls of TDM for supporting better implementation in the field of cancer treatment.

CONCLUSIONS

Adaptation of PKIs dosage regimens at the individual patient level, through a rational TDM approach, could prevent oncology patients from being exposed to ineffective or unnecessarily toxic drug concentrations in the era of personalized medicine.

Effect of Adherence on Pharmacokinetic/Pharmacodynamic Relationships of Oral Targeted Anticancer Drugs

The emergence of oral targeted anticancer agents transformed several cancers into chronic conditions with a need for long-term oral treatment. Although cancer is a life-threatening condition, oncology medication adherence-the extent to which a patient follows the drug regimen that is intended by the prescriber-can be suboptimal in the long term, as in any other chronic disease. Poor adherence can impact negatively on clinical outcomes, notably because most of these drugs are given as a standard non-individualized dosage despite marked inter-individual variabilities that can lead to toxic or inefficacious drug concentrations. This has been especially studied with the prototypal drug imatinib. In the context of therapeutic drug monitoring (TDM), increasingly advocated for oral anticancer treatment optimization, unreported suboptimal adherence affecting drug intake history may lead to significant bias in the concentration interpretation and inappropriate dosage adjustments. In the same way, suboptimal adherence may also bias the results of pharmacokinetic modeling studies, which will affect in turn Bayesian TDM interpretation that relies on such population models. Detailed knowledge of the influence of adherence on plasma concentrations in pharmacokinetic studies or in routine TDM programs is however presently missing in the oncology field. Studies on this topic are therefore eagerly awaited to better pilot the treatment of cancer with the new targeted agents and to find their optimal dosage regimen. Hence, the development and assessment of effective medication adherence programs are warranted for these treatments.

Estimation of tenofovir's population pharmacokinetic parameters without reliable dosing histories and application to tracing dosing history using simulation strategies

The objectives of this analysis were to develop a population pharmacokinetic model (PPK) for tenofovir without using potentially unreliable patient reported dosing records and to retrace patient dosing history using pharmacokinetic simulations conditioned on protocol design constraints to assess patient adherence. MTN-001 is a multi-center, open label, 3-way cross over study comparing oral, vaginal and combination (oral and vaginal) administration of tenofovir in healthy women. It was reported that self-reported adherence in this study was high (94%), but serum concentrations indicated only 64% of participants used tablets consistently. A method based on superposition was applied to develop the population PPK considering only observable clinic visit dosing information. A two compartment model described the data well and the parameters agree with the literature reported values. Race was not a significant covariate on clearance. Retracing of the dosing history with 3-past dose resolution was not successful. Trial simulations with full adherence assumption predict a median Cmin of 68 ng/mL, which is in agreement with literature reports. Non-adherence at 25% resulted in 37-51% reduction in Cmin using one coin and two coin models, respectively. Population analyses should consider some method of correction for non-adherence to avoid biased estimates.

An automated system for detecting nonadherence in laboratory testing and monitoring for myelosuppression in patients receiving self-administered oral chemotherapy

INTRODUCTION

Patient compliance with routine monitoring for self-administered chemotherapy is problematic. We sought to assess monitoring lapses and incidents of myelosuppression in patients undergoing self-administered chemotherapy for glioblastoma, as well as test software designed to detect and alert clinicians to lapses in monitoring.

PATIENTS AND METHODS

A retrospective analysis was conducted to identify patients (N=117) who received standard oral temozolomide for glioblastoma at our institution from 2003 to 2010. Gaps in monitoring were classified as minor (10 to 12 days) or major (13 to 28 days), and adverse events were graded using standard criteria. During the prospective portion of the study, we tested a software-based system that alerted clinicians of monitoring lapses and adverse events among patients receiving self-administered temozolomide for glioblastoma (n=37).

RESULTS

Our retrospective review found that 34 of 117 patients experienced monitoring gaps during treatment. No association between gaps and risk of myelosuppression were found. Patients with gaps were more likely to be male (P=.04). Patients monitored prospectively with the software experienced no major gaps in monitoring (P=.007 compared with retrospective patients).

CONCLUSION

Our retrospective review demonstrated that monitoring nonadherence was occurring at a substantial rate. Our computerized system eliminated major gaps in monitoring in the prospective portion of our study. Although there is no association between monitoring gaps and the occurrence of adverse events, when they do coincide, continuing oral chemotherapy during an unrecognized adverse event may worsen the patient's condition. Automated systems are justified and serve a function not currently being addressed.

A Bayesian approach for the estimation of patient compliance based on the last sampling information

Poor adherence to a drug prescription significantly impacts on the efficacy and safety of a planned therapy. The relationship between drug intake and pharmacokinetics (PK) is only partially known. In this work, we focus on the so-called "inverse problem", concerned with the issue of retracing the patient compliance scenario using limited clinical knowledge. Using a reported Pop-PK model of imatinib, and accounting for the variability around its PK parameters, we were able to simulate a whole range of drug concentration values at a specific sampling point for a population of patients with all possible drug compliance profiles. Using a Bayesian decision rule, we developed a methodology for the determination of the associated compliance profile prior to a given sampling value. The adopted approach allows, for the first time, to quantitatively acquire knowledge about the compliance patterns having a causal effect on a given PK. Moreover, using a simulation approach, we were able to evaluate the evolution of success rate of the retracing process in terms of the considered time period before sampling as well as the model-inherited variability. In conclusion, this work allows, from a probability viewpoint, to propose a solution for this inverse problem of compliance determination.

The hand-foot-syndrome associated with medical tumor therapy - classification and management

The hand-foot-syndrome (HFS, palmoplantar erythrodysesthesia, chemotherapy-associated acral erythema) is characterized by painful predominantly palmo-plantar lesions. The association with different chemotherapeutic agents has been known for over 20 years. More recently, HFS has been reported in association with regimens using targeted agents, in particular the multikinase inhibitors (MKI) sorafenib and sunitinib. The HFS associated with MKI has a different distribution and clinical appearance than the traditional disorder. In this review, similarities and differences between chemotherapy- and MKI-associated HFS are discussed and current recommendations for their prophylaxis and management are summarized.