A limited sampling schedule to estimate individual pharmacokinetics of pemetrexed in patients with varying renal functions

Purpose: Pemetrexed is a widely used cytostatic agent with an established exposure–response relationship. Although dosing is based on body surface area (BSA), large interindividual variability in pemetrexed plasma concentrations is observed. Therapeutic drug monitoring (TDM) can be a feasible strategy to reduce variability in specific cases leading to potentially optimized pemetrexed treatment. The aim of this study was to develop a limited sampling schedule (LSS) for the assessment of pemetrexed pharmacokinetics. Methods: Based on two real-life datasets, several limited sampling designs were evaluated on predicting clearance, using NONMEM, based on mean prediction error (MPE %) and normalized root mean squared error (NRMSE %). The predefined criteria for an acceptable LSS were: a maximum of four sampling time points within 8 h with an MPE and NRMSE ≤ 20%. Results: For an accurate estimation of clearance, only four samples in a convenient window of 8 h were required for accurate and precise prediction (MPE and NRMSE of 3.6% and 5.7% for dataset 1 and of 15.5% and 16.5% for dataset 2). A single sample at t = 24 h performed also within the criteria with MPE and NRMSE of 5.8% and 8.7% for dataset 1 and of 11.5% and 16.4% for dataset 2. Bias increased when patients had lower creatinine clearance. Conclusions: We presented two limited sampling designs for estimation of pemetrexed pharmacokinetics. Either one can be used based on preference and feasibility

Population Pharmacokinetic Model and Pharmacokinetic Target Attainment of Micafungin in Intensive Care Unit Patients

_Objective:_ To study the pharmacokinetics of micafungin in intensive care patients and assess pharmacokinetic (PK) target attainment for various dosing strateg

A New Framework to Implement Model-Informed Dosing in Clinical Guidelines: Piperacillin and Amikacin as Proof of Concept

Background: Modeling and simulation is increasingly used to study pediatric pharmacokinetics, but clinical implementation of age-appropriate doses lags behind. Therefore, we aimed to develop model-informed doses using published pharmacokinetic data and a decision framework to adjust dosing guidelines based on these doses, using piperacillin and amikacin in critically ill children as proof of concept. Methods: Piperacillin and amikacin pharmacokinetic models in critically ill children were extracted from literature. Concentration-time profiles were simulated for various dosing regimens for a virtual PICU patient dataset, including the current DPF dose and doses proposed in the studied publications. Probability of target attainment (PTA) was compared between the different dosing regimens. Next, updated dosing recommendations for the DPF were proposed, and evaluated using a new framework based on PK study quality and benefit-risk analysis of clinical implementation. Results: Three studies for piperacillin (

Ultrafast and high-throughput mass spectrometric assay for therapeutic drug monitoring of antiretroviral drugs in pediatric HIV-1 infection applying dried blood spots

Kaletra® (Abott Laboratories) is a co-formulated medication used in the treatment of HIV-1-infected children, and it contains the two antiretroviral protease inhibitor drugs lopinavir and ritonavir. We validated two new ultrafast and high-throughput mass spectrometric assays to be used for therapeutic drug monitoring of lopinavir and ritonavir concentrations in whole blood and in plasma from HIV-1-infected children. Whole blood was blotted onto dried blood spot (DBS) collecting cards, and plasma was collected simultaneously. DBS collecting cards were extracted by an acetonitrile/water mixture while plasma samples were deproteinized with acetone. Drug concentrations were determined by matrix-assisted laser desorption/ionization-triple quadrupole tandem mass spectrometry (MALDI-QqQ-MS/MS). The application of DBS made it possible to measure lopinavir and ritonavir in whole blood in therapeutically relevant concentrations. The MALDI-QqQ-MS/MS plasma assay was successfully cross-validated with a commonly used high-performance liquid chromatography (HPLC)–ultraviolet (UV) assay for the therapeutic drug monitoring (TDM) of HIV-1-infected patients, and it showed comparable performance characteristics. Observed DBS concentrations showed as well, a good correlation between plasma concentrations obtained by MALDI-QqQ-MS/MS and those obtained by the HPLC-UV assay. Application of DBS for TDM proved to be a good alternative to the normally used plasma screening. Moreover, collection of DBS requires small amounts of whole blood which can be easily performed especially in (very) young children where collection of large whole blood amounts is often not possible. DBS is perfectly suited for TDM of HIV-1-infected children; but nevertheless, DBS can also easily be applied for TDM of patients in areas with limited or no laboratory facilities

Non-linear protein binding of phenytoin in clinical practice - development and validation of a mechanistic prediction model

Aims: To individualize treatment, phenytoin doses are adjusted based on free concentrations, either measured or calculated from total concentrations. As a mechanistic protein binding model may more accurately reflect the protein binding of phenytoin than the empirical Winter–Tozer equation that is routinely used for calculation of free concentrations, we aimed to develop and validate a mechanistic phenytoin protein binding model. Methods: Data were extracted from routine clinical practice. A mechanistic drug protein binding model was developed using nonlinear mixed effects modelling in a development dataset. The predictive performance of the mechanistic model was then compared with the performance of the Winter–Tozer equation in 5 external datasets. Results: We found that in the clinically relevant concentration range, phenytoin protein binding is not only affected by serum albumin concentrations and presence of severe renal dysfunction, but is also concentration dependent. Furthermore, the developed mechanistic model outperformed the Winter–Tozer equation in 4 out of 5 datasets in predicting free concentrations in various populations. Conclusions: Clinicians should be aware that the free fraction changes when phenytoin exposure changes. A mechanistic binding model may facilitate prediction of free phenytoin concentrations from total concentrations, for example for dose individualization in the clinic

The effect of neutropenia on the clinical pharmacokinetics of vancomycin in adults

AIM: There is accumulating evidence that neutropenic patients require higher dosages of vancomycin. To prevent sub-therapeutic drug exposure, it is of utmost importance to obtain adequate exposure from the first dose onwards. We aimed to quantify the effect of neutropenia on the pharmacokinetics of vancomycin. METHODS: Data were extracted from a matched patient cohort of patients known with (1) hematological disease, (2) solid malignancy, and (3) patients not known with cancer. Pharmacokinetic analysis was performed using non-linear mixed effects modeling with neutropenia investigated as a binary covariate on clearance and volume of distribution of vancomycin. RESULTS: A total of 116 patients were included (39 hematologic patients, 39 solid tumor patients, and 38 patients not known with cancer). In total, 742 paired time-concentration observations were available for the pharmacokinetic analysis. Presence of neutropenia showed to significantly (p = 0.00157) increase the clearance of vancomycin by 27.7% (95% CI 10.2-46.2%), whereas it did not impact the volume of distribution (p = 0.704). CONCLUSIONS: This study shows that vancomycin clearance is increased in patients with neutropenia by 27.7%. Therefore, the vancomycin maintenance dose should be pragmatically increased by 25% in neutropenic patients at the start of treatment. Since the volume of distribution appeared unaffected, no adjustment in loading dose is required. These dose adjustments do not rule out the necessity of further dose individualization by means of therapeutic drug monitoring

A pharmacokinetic and pharmacogenetic study of efavirenz in children: dosing guidelines can result in subtherapeutic concentrations

BACKGROUND: Our main objectives were to study the population pharmacokinetics of efavirenz and to explore the adequacy of dosing guidelines. METHODS: A total of 33 HIV-1-infected patients were recruited from the Emma Children's Hospital (Amsterdam, the Netherlands). Gender, age, drug formulation, the presence of the c.516G>T polymorphism in the CYP2B6 gene and the quantitation of liver enzymes alanine aminotransferase and aspartate aminotransferase at baseline were collected. A non-linear mixed effect pharmacokinetic model was developed. RESULTS: CYP2B6 genotype and drug formulation significantly influenced efavirenz pharmacokinetics. Clearance was 29.7% lower in children carrying the CYP2B6-516-G/T genotype compared with children carrying the G/G genotype. Relative bioavailiability of the oral liquid compared with tablets or capsules was 46.6%. Children carrying the CYP2B6-516-G/G genotype had a 50-70% probability of developing a subtherapeutic trough level of efavirenz and only 1-3% probability of developing a trough level >4 mg/l. To reduce the probability of developing a subtherapeutic trough concentration, we propose to give an adult efavirenz dose to children weighing > or =25 kg and to allometrically scale doses for other weight levels a priori. The dose of the oral solution should be twice the dose of capsules. CONCLUSIONS: Population pharmacokinetics of efavirenz in children were adequately described. Current dosing guidelines can result in subtherapeutic concentrations in children carrying the CYP2B6-516-G/G genotype and with the liquid formulation. A priori dose adaptations in the paediatric population seem feasible and need prospective validatio

Optimized Dosing:The Next Step in Precision Medicine in Non-Small-Cell Lung Cancer

In oncology, and especially in the treatment of non-small-cell lung cancer (NSCLC), dose optimization is often a neglected part of precision medicine. Many drugs are still being administered in "one dose fits all" regimens or based on parameters that are often only minor determinants for systemic exposure. These dosing approaches often introduce additional pharmacokinetic variability and do not add to treatment outcomes. Fortunately, pharmacological knowledge is increasing, providing valuable information regarding the potential of, for example, therapeutic drug monitoring. This article focuses on the evidence for the most promising and easily implemented optimized dosing approaches for the small-molecule inhibitors, chemotherapeutic agents, and monoclonal antibodies as treatment options currently approved for NSCLC. Despite limitations such as investigations having been conducted in oncological diseases other than NSCLC or the retrospective origin of many analyses, an alternative dosing regimen could be beneficial for treatment outcomes, prescriber convenience, or financial burden on healthcare systems. This review of the literature provides recommendations on the implementation of dose optimization and advice regarding promising strategies that deserve further research in NSCLC