Population pharmacokinetics of busulfan in Saudi pediatric patients undergoing hematopoietic stem cell transplantation

Exploring the Pharmacokinetics of Drugs in Disabled Saudi Patients: A Systematic Review

Background/Objectives: Disability is a term that involves mental, intellectual, or sensory impairment resulting in the loss of one's ability to walk or perform the activities necessary to live in a society. This study aims to collect all the data regarding the absorption, distribution, and disposition of drugs in disabled Saudi patients, i.e., patients suffering from epilepsy, cancer, cardiovascular diseases, etc., and then compare these results with data reported in other ethnicities. Methods: An exhaustive online search used the key terms in Google Scholar, PubMed, Cochrane Library, and Science Direct to extract all articles that met the eligibility criteria. All research studies containing pharmacokinetic (PK) parameters (area under the curve from 0 to infinity (AUC0-∞), maximal plasma concentration (Cmax), clearance (CL), volume of distribution, time to reach maximum plasma concentration, and half-life) were included in this review. Results: In pediatric epileptic patients, carbamazepine showed a notable decrease in Cmax with increasing age, which may be due to ontogenetic changes in its disposition. The AUC0-∞ of busulphan in adult hematopoietic stem cell transplantation patients was recorded as 4392.5 ± 1354.65 μg·h/mL, with high inter-individual variability. Moreover, the CL of vancomycin was reported to be 25% higher among cancer patients in comparison to non-cancer subjects. Conclusions: The complications in disabled patients due to alterations in cytochrome P450 enzymes, pathophysiology, genetics, and ethnicity emphasize the significance of patient-centered drug dosing. These findings may aid healthcare physicians in refining therapeutic care in this population.

A retrospective analysis of tacrolimus pharmacokinetic in Saudi paediatric patients in early post-liver transplantation period

BACKGROUND

Tacrolimus is an essential immunosuppressive medication in paediatric patients' post-liver transplantation. Achieving tacrolimus target concentration in early post-transplantation is crucial to minimise the risk of acute rejection; however, this is challenging due to inter- and intra-patient variability in tacrolimus metabolism and clearance. Therefore, our study aims to describe tacrolimus trough concentration variability and pharmacokinetics in paediatric post-liver transplantation during the first two weeks post-transplantation.

METHOD

This retrospective multicentre observational study included paediatric patients post-liver transplantation. Post-operative data was collected within the initial 14 days using electronic health records, including daily tacrolimus doses, measured trough concentrations, graft data, surgical data, and documented acute rejection. Pharmacokinetic analysis was completed using the Monolix software. We used the empirical Bayesian estimates of clearance and volume of distribution for covariate testing to assess possible correlations. We performed a stepwise regression analysis (alpha = 0.05).

RESULTS

Ninety-one paediatric patients were included in the study, with a mean age of 4.1 years (SD = 4.6). The mean graft-to-recipient weight ratio (GRWR) was 3% (SD = 6). The vast majority of the patients received the liver from living donors (n = 84, 92.3%). The average time needed to reach therapeutic concentration was 4.6 (SD = 2.8) days. The initial clearance (Clini) was very low at baseline (0.012 L/h), then increased dramatically to 9.84 L/h at 14 days post-transplantation. The clearance appeared to be time-dependent, and the time needed to reach 50% of maximum clearance was five days post-transplantation. The covariates that significantly affected clearance included bodyweight and aspartate transaminase, while the only significant covariate for volume of distribution was bodyweight.

CONCLUSION

Tacrolimus is a drug with high intra- and interindividual variability, making dosing challenging in the paediatric liver transplantation population. Prospective studies with more intensive sampling are needed to address the time-dependent changes in clearance, which will aid in establishing the optimal dosing regimens in this population.

Simulation-Based Optimization of Sampling Schedules for Model-Informed Precision Dosing of Once-Daily and 4-Times-Daily Busulfan in Pediatric Patients

BACKGROUND

Therapeutic drug monitoring (TDM) is crucial in optimizing the outcomes of hematopoietic stem cell transplantation by guiding busulfan (Bu) dosing. Limited sampling strategies show promise for efficiently adjusting drug doses. However, comprehensive assessments and optimization of sampling schedules for Bu TDM in pediatric patients are limited. We aimed to establish optimal sampling designs for model-informed precision dosing (MIPD) of once-daily (q24h) and 4-times-daily (q6h) Bu administration in pediatric patients.

METHODS

Simulated data sets were used to evaluate the population pharmacokinetic model-based Bayesian estimation of the area under the concentration-time curve (AUC) for different limited sampling strategy designs. The evaluation was based on the mean prediction error for accuracy and root mean square error for precision. These findings were validated using patient-observed data. In addition, the MIPD protocol was implemented in the Tucuxi software, and its performance was assessed.

RESULTS

Our Bayesian estimation approach allowed for flexible sampling times while maintaining mean prediction error within ±5% and root mean square error below 10%. Accurate and precise AUC0-24h and cumulative AUC estimations were obtained using 2-sample and single-sample schedules for q6h and q24h dosing, respectively. TDM on 2 separate days was necessary to accurately estimate cumulative exposure, especially in patients receiving q6h Bu. Validation with observed patient data confirmed the precision of the proposed limited sampling scenarios. Implementing the MIPD protocol in Tucuxi software yielded reliable AUC estimations.

CONCLUSIONS

Our study successfully established precise limited sampling protocols for MIPD of Bu in pediatric patients. Our findings underscore the importance of TDM on at least 2 occasions to accurately achieve desired Bu exposures. The developed MIPD protocol and its implementation in Tucuxi software provide a valuable tool for routine TDM in pediatric hematopoietic stem cell transplantation.

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.

Population Pharmacokinetic Model of Intravenous Busulfan in Hematopoietic Cell Transplantation: Systematic Review and Comparative Simulations

BACKGROUND

Busulfan is commonly used in the chemotherapy prior to hematopoietic cell transplantation (HCT). Busulfan has a narrow therapeutic window and a well-established exposure-response relationship with important clinical outcomes. Model-informed precision dosing (MIPD) based on population pharmacokinetic (popPK) models has been implemented in the clinical settings. We aimed to systematically review existing literature on popPK models of intravenous busulfan.

METHODS

We systematically searched Ovid MEDLINE, EMBASE, Cochrane Library, Scopus, and Web of Science databases from inception to December 2022 to identify original popPK models (nonlinear mixed-effect modeling) of intravenous busulfan in HCT population. Model-predicted busulfan clearance (CL) was compared using US population data.

RESULTS

Of the 44 eligible popPK studies published since 2002, 68% were developed predominantly in children, 20% in adults, and 11% in both children and adults. The majority of the models were described using first-order elimination or time-varying CL (69% and 26%, respectively). All but three included a body-size descriptor (e.g., body weight, body surface area). Other commonly included covariates were age (30%) and GSTA1 variant (15%). Median between-subject and between-occasion variabilities of CL were 20% and 11%, respectively. Between-model variabilities in predicted median CL were < 20% in all of the weight tiers (10-110 kg) in the simulation based on US population data.

CONCLUSION

Busulfan PK is commonly described using a first-order elimination or time-varying CL. A simple model with limited covariates were generally sufficient to attain relatively small unexplained variabilities. However, therapeutic drug monitoring may still be necessary to attain a narrow target exposure.

Can First-Dose Therapeutic Drug Monitoring Predict the Steady State Area Under the Blood Concentration-Time Curve of Busulfan in Pediatric Patients Undergoing Hematopoietic Stem Cell Transplantation?

Busulfan has high intra-individual variability and possible time-dependent changes in clearance, which complicates therapeutic drug monitoring (TDM), as first dose sampling may not predict the steady state concentrations. In this study, we aimed to use Bayesian pharmacokinetic parameters estimated from the first dose to predict the steady state AUC for busulfan. This observational study was conducted among pediatric patients at King Abdullah Specialist Children's Hospital. From each patient, we collected six blood samples (2, 2.25, 2.5, 3, 4, and 6 h after the start of IV infusion of the first dose). A subset of patients were also sampled at the steady state. First, we modeled the data using only the first dose. The model was used to estimate the empirical Bayesian estimates of clearance for each individual patient, then we used the empirical Bayesian estimates of clearance to predict the AUC_0-tau at steady state (i.e., predicted AUC_0-tau). Steady state AUC_0-tau was also calculated for patients sampled at steady state using the trapezoidal method using raw time concentration data; this was considered the reference AUC_0-tau.. Then, we compared the AUC_0-tau predicted using the Bayesian approach with the reference AUC_0-tau values. We calculated bias and precision to assess predictability. In total we had 33 patients sampled after first dose and at steady state. Using the Bayesian approach to predict the AUC_0-tau, bias was -2.8% and precision was 33%. This indicates that first dose concentrations cannot accurately predict steady state busulfan concentrations; therefore, follow-up TDM may be required for optimal dosing.