Population pharmacokinetics of treosulfan and development of a limited sampling strategy in children prior to hematopoietic stem cell transplantation

Outcomes from hematopoietic stem cell transplantation following treosulfan-based conditioning: A clinical and pharmacokinetic analysis

BACKGROUND

The aims of this study are to report our experience with treosulfan-based conditioning regimens for patients with non-malignant hematologic conditions, correlating clinical outcomes at different time points post-transplant with treosulfan exposure (AUC).

METHODS

This study was a single-center observational study investigating overall survival (OS), disease-free survival (DFS), and event-free survival (EFS) end-points post-transplant. The consequences of treosulfan AUC with respect to toxicity, correction of underlying disease, and long-term chimerism were also explored using pharmacokinetic analysis.

RESULTS

Forty-six patients received 49 transplants with treosulfan and fludarabine-based conditioning between 2005 and 2023. Twenty-four patients also received thiotepa. Donor chimerism was assessed on either whole blood or sorted cell lines at different time points post-transplant. Thirty-nine patients received treosulfan pharmacokinetic assessment to evaluate cumulative AUC, with five infants receiving real-time assessment to facilitate daily dose adjustment. OS, DFS, and EFS were 87%, 81%, and 69%, respectively. Median follow-up was 32.1 months (range 0.82-160 months) following transplant. Lower EFS was associated with patient age (<1 year; p = .057) and lower cumulative treosulfan dose (<42 g/m2; p = .003). Stable donor chimerism in B-cell, NK-cell, and granulocyte lineages at 1-year post-transplant were more prevalent in patients receiving thiotepa conditioning. Two infants required daily dose adjustment to treosulfan to avoid high AUC.

CONCLUSIONS

Excellent clinical outcomes and stable chimerism were observed in this patient series. The addition of thiotepa conferred no significant toxicity and trended toward sustained ongoing donor engraftment. Correlating treosulfan AUC with long-term patient outcomes is required.

Treosulfan vs busulfan conditioning for allogeneic bmt in children with nonmalignant disease: a randomized phase 2 trial

Optimal conditioning prior to allogeneic hematopoietic stem cell transplantation for children with non-malignant diseases is subject of ongoing research. This prospective, randomized, phase 2 trial compared safety and efficacy of busulfan with treosulfan based preparative regimens. Children with non-malignant diseases received fludarabine and either intravenous (IV) busulfan (4.8 to 3.2 mg/kg/day) or IV treosulfan (10, 12, or 14 g/m2/day). Thiotepa administration (2 × 5 mg/kg) was at the investigator's discretion. Primary endpoint was freedom from transplantation (treatment)-related mortality (freedom from TRM), defined as death between Days -7 and +100. Overall, 101 patients (busulfan 50, treosulfan 51) with at least 12 months follow-up were analyzed. Freedom from TRM was 90.0% (95% CI: 78.2%, 96.7%) after busulfan and 100.0% (95% CI: 93.0%, 100.0%) after treosulfan. Secondary outcomes (transplantation-related mortality [12.0% versus 3.9%]) and overall survival (88.0% versus 96.1%) favored treosulfan. Graft failure was more common after treosulfan (n = 11), than after busulfan (n = 2) while all patients were rescued by second procedures except one busulfan patient. CTCAE Grade III adverse events were similar in both groups. This study confirmed treosulfan to be an excellent alternative to busulfan and can be safely used for conditioning treatment in children with non-malignant disease.

Treosulfan Exposure Predicts Thalassemia-Free Survival in Patients with Beta Thalassemia Major Undergoing Allogeneic Hematopoietic Cell Transplantation

A toxicity-reduced conditioning regimen with treosulfan, fludarabine, and thiotepa in patients with high-risk β-thalassemia major has significantly improved hematopoietic stem cell transplantation (HCT) outcomes. However, complications resulting from regimen-related toxicities (RRTs), mixed chimerism, and graft rejection remain a challenge. We evaluated the dose-exposure-response relationship of treosulfan and its active metabolite S, S-EBDM, in a uniform cohort of patients with β-thalassemia major to identify whether therapeutic drug monitoring (TDM) and dose adjustment of treosulfan is feasible. Plasma treosulfan/S, S-EBDM levels were measured in 77 patients using a validated liquid chromatography with tandem mass spectrometry method, and the pharmacokinetic parameters were estimated using nlmixr2. The influence of treosulfan and S, S-EBDM exposure, and GSTA1/NQO1 polymorphisms on graft rejection, RRTs, chimerism status, and 1-year overall survival (OS), and thalassemia-free survival (TFS) were assessed. We observed that treosulfan exposure was lower in patients with graft rejection than those without (1,655 vs. 2,037 mg•h/L, P = 0.07). Pharmacodynamic modeling analysis to identify therapeutic cutoff revealed that treosulfan exposure ≥1,660 mg•hour/L was significantly associated with better 1-year TFS (97% vs. 81%, P = 0.02) and a trend to better 1-year OS (90% vs. 69%, P = 0.07). Further, multivariate analysis adjusting for known pre-HCT risk factors also revealed treosulfan exposure <1,660 mg•h/L (hazard ratio (HR) = 3.23; 95% confidence interval (CI) = 1.12-9.34; P = 0.03) and GSTA1*B variant genotype (HR = 3.75; 95% CI = 1.04-13.47; P = 0.04) to be independent predictors for inferior 1-year TFS. We conclude that lower treosulfan exposure increases the risk of graft rejection and early transplant-related mortality affecting TFS. As no RRTs were observed with increasing treosulfan exposure, TDM-based dose adjustment could be feasible and beneficial.

Population pharmacokinetic modeling of treosulfan and rationale for dose recommendation in children treated for conditioning prior to allogeneic hematopoietic stem cell transplantation

Intravenously infused treosulfan was evaluated in adult and pediatric patients for conditioning regimen prior to allogeneic hematopoietic stem cell transplantation. A population pharmacokinetic (PK) model was initially developed on 116 adult and pediatric PK profiles from historical trials, to support treosulfan dose recommendations for children in 2 prospective trials. The aim was to assess and update the initial population PK model by inclusion of additional 83 pediatric PK profiles from these 2 trials. The final population PK model was 2-compartmental with dosing in the central compartment, linear elimination, and inter-compartmental clearance. Inter-individual variability was included on clearance (CL), central volume (V1), peripheral volume (V2), and inter-compartmental clearance (Q). The final model described an effect of the body surface area (BSA) on CL, V1, V2, and Q. The final model resulted in a modified dose recommendation for children and advises treosulfan doses of 10 g/m2, 12 g/m2, and 14 g/m2 for BSAs of <0.4 m2, ≥0.4 to <0.9 m2, and ≥0.9 m2, respectively. This simplified BSA-dependent dose recommendation was developed for children, ensuring a well comparable treosulfan exposure as a dose of 14 g/m2 in adults - irrespective of their age and without applying individual therapeutic drug monitoring.

Impact of Treosulfan Exposure on Early and Long-Term Clinical Outcomes in Pediatric Allogeneic Hematopoietic Stem Cell Transplantation Recipients: A Prospective Multicenter Study

Treosulfan-based conditioning has gained popularity in pediatric allogeneic hematopoietic stem cell transplantation (HSCT) because of its presumed favorable efficacy and toxicity profile. Treosulfan is used in standardized dosing regimens based on body surface area. The relationships between systemic treosulfan exposure and early and long-term clinical outcomes in pediatric patients undergoing allogeneic HSCT for nonmalignant diseases remain unclear. In this a multicenter, prospective observational study, we assessed the association between treosulfan exposure and early and, in particular, long-term clinical outcomes. Our study cohort comprised 110 pediatric patients with nonmalignant diseases who underwent HSCT between 2011 and 2019 in Leiden, The Netherlands and Rome, Italy. Blood samples were collected, and treosulfan area under the receiver operating characteristic curve (AUC_0-∞) was estimated as a measure of exposure. Cox proportional hazard survival analyses were performed to assess the relationships between treosulfan exposure and overall survival (OS) and event-free survival (EFS). The predictive value of systemic treosulfan exposure for the occurrence of toxicity within 28 days was evaluated using a multivariable logistic regression analysis. In the overall cohort, OS and EFS at 2 years were 89.0% and 75.3%, respectively, with an excellent OS of 97% in children age <2 years. The occurrence of grade II-IV acute graft-versus-host disease, the level of 1-year whole blood chimerism, and 2-year OS and EFS were not correlated with treosulfan exposure. The occurrence of skin toxicity (odds ratio [OR], 3.97; 95% confidence interval [CI], 1.26-13.68; P = .02) and all-grade mucositis (OR, 4.43; 95% CI, 1.43-15.50; P = .02), but not grade ≥2 mucositis (OR, 1.51; 95% CI, 0.52 to 4.58; P = .46) was related to high treosulfan exposure (>1750 mg*h/L). Our study demonstrates that standardized treosulfan-based conditioning results in a favorable OS and EFS in infants and children with nonmalignant diseases, independent of interindividual variation in treosulfan exposure. These outcomes can be achieved without the need for therapeutic drug monitoring, thereby emphasizing the advantage of treosulfan use in this category of patients. Although higher treosulfan exposure increases the risk of skin toxicity, there is no absolute necessity for therapeutic drug monitoring if proper preventive skin measures are taken. More research is needed to assess whether deescalation of treosulfan doses is possible to minimize early and long-term toxicity without compromising efficacy.

Population pharmacokinetic modelling of intravenous immunoglobulin in patients with predominantly antibody deficiencies

AIMS

There is considerable interpatient variability in the pharmacokinetics (PK) of intravenous immunoglobulin G (IVIG), causing difficulty in optimizing individual dosage regimen. This study aims to estimate the population PK parameters of IVIG and to investigate the impact of genetic polymorphism of the FcRn gene and clinical variability on the PK of IVIG in patients with predominantly antibody deficiencies.

METHODS

Patients were recruited from four hospitals. Clinical data were recorded and blood samples were taken for PK and genetic studies. Population PK parameters were estimated by nonlinear mixed-effects modelling in Monolix®. Models were evaluated using the difference in objective function value, goodness-of-fit plots, visual predictive check and bootstrap analysis. Monte Carlo simulation was conducted to evaluate different dosing regimens for IVIG.

RESULTS

A total of 30 blood samples were analysed from 10 patients. The immunoglobulin G concentration data were best described by a one-compartment model with linear elimination. The final model included both volume of distribution (Vd) and clearance (CL) based on patient's individual weight. Goodness-of-fit plots indicated that the model fit the data adequately, with minor model mis-specification. Genetic polymorphism of the FcRn gene and the presence of bronchiectasis did not affect the PK of IVIG. Simulation showed that 3-4-weekly dosing intervals were sufficient to maintain IgG levels of 5 g L^-1 , with more frequent intervals needed to achieve higher trough levels.

CONCLUSIONS

Body weight significantly affects the PK parameters of IVIG. Genetic and other clinical factors investigated did not affect the disposition of IVIG.

Total Body Irradiation Forever? Optimising Chemotherapeutic Options for Irradiation-Free Conditioning for Paediatric Acute Lymphoblastic Leukaemia

Total-body irradiation (TBI) based conditioning prior to allogeneic hematopoietic stem cell transplantation (HSCT) is generally regarded as the gold-standard for children >4 years of age with acute lymphoblastic leukaemia (ALL). Retrospective studies in the 1990's suggested better survival with irradiation, confirmed in a small randomised, prospective study in the early 2000's. Most recently, this was reconfirmed by the early results of the large, randomised, international, phase III FORUM study published in 2020. But we know survivors will suffer a multitude of long-term sequelae after TBI, including second malignancies, neurocognitive, endocrine and cardiometabolic effects. The drive to avoid TBI directs us to continue optimising irradiation-free, myeloablative conditioning. In chemotherapy-based conditioning, the dominant myeloablative effect is provided by the alkylating agents, most commonly busulfan or treosulfan. Busulfan with cyclophosphamide is a long-established alternative to TBI-based conditioning in ALL patients. Substituting fludarabine for cyclophosphamide reduces toxicity, but may not be as effective, prompting the addition of a third agent, such as thiotepa, melphalan, and now clofarabine. For busulfan, it's wide pharmacokinetic (PK) variability and narrow therapeutic window is well-known, with widespread use of therapeutic drug monitoring (TDM) to individualise dosing and control the cumulative busulfan exposure. The development of first-dose selection algorithms has helped achieve early, accurate busulfan levels within the targeted therapeutic window. In the future, predictive genetic variants, associated with differing busulfan exposures and toxicities, could be employed to further tailor individualised busulfan-based conditioning for ALL patients. Treosulfan-based conditioning leads to comparable outcomes to busulfan-based conditioning in paediatric ALL, without the need for TDM to date. Future PK evaluation and modelling may optimise therapy and improve outcome. More recently, the addition of clofarabine to busulfan/fludarabine has shown encouraging results when compared to TBI-based regimens. The combination shows activity in ALL as well as AML and deserves further evaluation. Like busulfan, optimization of chemotherapy conditioning may be enhanced by understanding not just the PK of clofarabine, fludarabine, treosulfan and other agents, but also the pharmacodynamics and pharmacogenetics, ideally in the context of a single disease such as ALL.

Estimation of the area under concentration-time curve of polymyxin B based on limited sampling concentrations in Chinese patients with severe pneumonia

AIMS

The efficacy and toxicity of polymyxin B (PB) are closely related to its pharmacokinetic/pharmacodynamic (PK/PD) index area under the concentration-time curve (AUC) to minimum inhibitory concentration (MIC) ratio. The purpose of this study was to obtain PK data for PB in Chinese severe pneumonia patients and establish appropriate blood sampling time points for the PB therapeutic drug monitoring (TDM).

SUBJECT AND METHOD

After treatment with at least four doses of PB (50 IU, q12h), the blood samples were collected immediately after the end of infusion (C₀) and 1.5, 2, 4, 6, 8, and 12 h (C_1.5, C₂, C₄, C₆, C₈, C₁₂) after PB administration. The PB blood plasma concentrations were determined using an ultra-performance liquid chromatography-tandem mass spectrometer (UPLC-MS/MS). All 42 patients were randomly divided into modeling (n = 24) and validation (n = 18) groups. The relationship between AUC_ss,24h and PB plasma concentration at each time point in modeling group was analyzed using limited sampling strategy and a PK method based on one-compartment with correction model.

RESULTS

C₆ scheme was found to provide the most accurate prediction of AUC_ss,24h values (r² = 0.984) with the target value of 1.9-4.2 μg/ml at steady state to reach the 50-100 μg h/ml criteria of AUC_ss,24h. C₀ with target value of 1.0-2.8 μg/ml can be considered an alternative sampling scheme (r² = 0.900) but prediction deviation may exist. C₀ and C_max sampling scheme also demonstrated good predicting ability of AUC values using PK model.

CONCLUSION

This study provides a clear plan for the implementation of TDM of PB, which is useful for optimizing the dosing regimen and individualizing treatment in severe pneumonia patients.

Population pharmacokinetic approach for evaluation of treosulfan and its active monoepoxide disposition in plasma and brain on the basis of a rat model

PURPOSE

Efficacy of treosulfan, used in the treatment of marrow disorders, depends on the activity of its monoepoxy-(EBDM) and diepoxy compounds. The study aimed to describe the pharmacokinetics of treosulfan and EBDM in the rat plasma and brain by means of mixed-effects modelling.

METHODS

The study had a one-animal-per-sample design and included ninty-six 10-week-old Wistar rats of both sexes. Treosulfan and EBDM concentrations in the brain and plasma were measured by an HPLC-MS/MS method. The population pharmacokinetic model was established in NONMEM software with a first-order estimation method with interaction.

RESULTS

One-compartment pharmacokinetic model best described changes in the concentrations of treosulfan in plasma, and EBDM concentrations in plasma and in the brain. Treosulfan concentrations in the brain followed a two-compartment model. Both treosulfan and EBDM poorly penetrated the blood-brain barrier (ratio of influx and efflux clearances through the blood-brain barrier was 0.120 and 0.317 for treosulfan and EBDM, respectively). Treosulfan plasma clearance was significantly lower in male rats than in females (0.273 L/h/kg vs 0.419 L/h/kg).

CONCLUSIONS

The developed population pharmacokinetic model is the first that allows the prediction of treosulfan and EBDM concentrations in rat plasma and brain. These results provide directions for future studies on treosulfan regarding the contribution of transport proteins or the development of a physiological-based model.

Modelling of neutrophil dynamics in children receiving busulfan or treosulfan for haematopoietic stem cell transplant conditioning

AIMS

Busulfan and treosulfan are cytotoxic agents used in the conditioning regime prior to paediatric haematopoietic stem cell transplantation (HSCT). These agents cause suppression of myeloid cells leaving patients severely immunocompromised in the early post-HSCT period. The main objectives were: (i) to establish a mechanistic pharmacokinetic-pharmacodynamic (PKPD) model for the treatment and engraftment effects on neutrophil counts comparing busulfan and treosulfan-based conditioning, and (ii) to explore current dosing schedules with respect to time to HSCT.

METHODS

Data on 126 patients, 72 receiving busulfan (7 months-18 years, 5.1-47.0 kg) and 54 treosulfan (4 months-17 years, 3.8-35.8 kg), were collected. In total, 8935 neutrophil count observations were recorded during the study period in addition to drug concentrations to develop a mechanistic PKPD model. Absolute neutrophil count profiles were modelled semimechanistically, accounting for transplant effects and differing set points pre- and post-transplant.

RESULTS

PK were best described by 2-compartment models for both drugs. The Friberg semimechanistic neutropenia model was applied with a linear model for busulfan and a maximum efficacy model for treosulfan describing drug effects at various stages of neutrophil maturation. System parameters were consistent across both drugs. The HSCT was represented by an amount of progenitor cells enhancing the neutrophils' proliferation and maturation compartments. Alemtuzumab was found to enhance the proliferative rate under which the absolute neutrophil count begin to grow after HSCT.

CONCLUSION

A semimechanistic PKPD model linking exposure to either busulfan or treosulfan to the neutrophil reconstitution dynamics was successfully built. Alemtuzumab coadministration enhanced the neutrophil proliferative rate after HSCT. Treosulfan administration was suggested to be delayed with respect to time to HSCT, leaving less time between the end of the administration and stem cell infusion.

Proposed Therapeutic Range of Treosulfan in Reduced Toxicity Pediatric Allogeneic Hematopoietic Stem Cell Transplant Conditioning: Results From a Prospective Trial

Treosulfan is given off‐label in pediatric allogeneic hematopoietic stem cell transplant. This study investigated treosulfan's pharmacokinetics (PKs), efficacy, and safety in a prospective trial. Pediatric patients (n = 87) receiving treosulfan‐fludarabine conditioning were followed for at least 1 year posttransplant. PKs were described with a two‐compartment model. During follow‐up, 11 of 87 patients died and 12 of 87 patients had low engraftment (≤ 20% myeloid chimerism). For each increase in treosulfan area under the curve from zero to infinity (AUC_(0‐∞)) of 1,000 mg hour/L the hazard ratio (95% confidence interval) for mortality increase was 1.46 (1.23–1.74), and the hazard ratio for low engraftment was 0.61 (0.36–1.04). A cumulative AUC_(0‐∞) of 4,800 mg hour/L maximized the probability of success (> 20% engraftment and no mortality) at 82%. Probability of success with AUC_(0‐∞) between 80% and 125% of this target were 78% and 79%. Measuring PK at the first dose and individualizing the third dose may be required in nonmalignant disease.

Treosulfan Pharmacokinetics and its Variability in Pediatric and Adult Patients Undergoing Conditioning Prior to Hematopoietic Stem Cell Transplantation: Current State of the Art, In-Depth Analysis, and Perspectives

Treosulfan is a prodrug that undergoes a highly pH- and temperature-dependent nonenzymatic conversion to the monoepoxide {(2S,3S)-1,2-epoxy-3,4-butanediol 4-methanesulfonate [S,S-EBDM]} and diepoxide {(2S,3S)-1,2:3,4-diepoxybutane [S,S-DEB]}. Currently, treosulfan is tested in clinical trials as an alternative to busulfan in conditioning prior to hematopoietic stem cell transplantation (HSCT). Of note, the optimal dosing of the prodrug is still unresolved, especially in infants. In this paper, the pharmacokinetics of treosulfan, together with its biologically active epoxides, is comprehensively reviewed for the first time, with the focus on conditioning prior to HSCT. Most of the insightful data presented in this review comes from studies that have been conducted in the last 3 years. The article widely discusses the volume of distribution and total clearance of treosulfan. In particular, the interindividual variability of these key parameters in infants, children above 1 year of age, and adults is analyzed, including possible covariates. A clinically important aspect of the formation rate-limited elimination of S,S-EBDM and S,S-DEB is described, including the correlation between the exposure of the prodrug and S,S-EBDM in children. The significance of the elimination half-life of treosulfan and its epoxides for successful conditioning prior to HSCT is also raised. Furthermore, the organ disposition of treosulfan and S,S-EBDM in rats is discussed in the context of the clinical toxicity and myeloablative activity of treosulfan versus busulfan. Moreover, perspectives for future therapeutic drug monitoring of treosulfan are presented. The review is intended to be helpful to pharmacists and doctors in the comprehension of the clinical pharmacokinetics of treosulfan.

Population pharmacokinetics of treosulfan in paediatric patients undergoing hematopoietic stem cell transplantation

Aims

Treosulfan is an alkylating agent increasingly used prior to haematopoietic stem cell transplantation. The aim of this study was to develop a population pharmacokinetic (PK) model of treosulfan in paediatric haematopoietic stem cell transplantation recipients and to explore the effect of potential covariates on treosulfan PK. Also, a limited sampling model (LSM) will be developed to accurately predict treosulfan exposure suitable for a therapeutic drug monitoring setting.

Methods

In this multicentre study, 91 patients, receiving a total dose of 30, 36 or 42 g/m² treosulfan, administered over 3 consecutive days, were enrolled. A population PK model was developed and demographic factors, as well as laboratory parameters, were included as potential covariates. In addition, a LSM was developed using data from 28 patients.

Results

A 2‐compartment model with first order elimination best described the data. Bodyweight with allometric scaling and maturation function were identified as significant predictors of treosulfan clearance. Treosulfan clearance reaches 90% of adult values at 4 postnatal years. A model‐based dosing table is presented to target an exposure of 1650 mg*h/L (population median) for different weight and age groups. Samples taken at 1.5, 4 and 7 hours after start of infusion resulted in the best limited sampling strategy.

Conclusions

This study provides a treosulfan population PK model in children and captures the developmental changes in clearance. A 3‐point LSM allows for accurate and precise estimation of treosulfan exposure.

Pre-formulation investigations for establishing a protocol for treosulfan handling and activation

INTRODUCTION

Treosulfan is an alkylating agent that is used for the treatment of ovarian cancer and for conditioning prior to stem cell transplantation. It is a prodrug that is activated non-enzymatically to two active epoxides.

OBJECTIVES

To optimize a protocol for both in vivo samples handling and in vitro drug preparation. Treosulfan stability was tested in biological fluids at different conditions as well as for its cytotoxicity on cell lines.

RESULTS

Plasma samples can be safely frozen for a short period up to 8 h, however; for longer periods, samples should be acidified. Urine samples and cell culture media can be safely frozen regardless their pH. For in vitro investigations, incubation of treosulfan at 37 °C for 24 h activated 100% of the drug. Whole blood acidification should be avoided for the risk of hemolysis. Finally; treosulfan cytotoxicity on HL-60 cells has increased following pre-incubation for 24 h at 37 °C compared to K562 cell line.

CONCLUSION

The stability profiling of treosulfan provided a valuable reference for handling of biological samples for both in vivo and in vitro studies. These results can be utilized for further investigations concerning the drug kinetics and dynamics in addition to the development of new pharmaceutical formulations.

Clinical bioanalysis of treosulfan and its epoxides: The importance of collected blood processing for valid pharmacokinetic results

Currently, there is an urgent need to establish the optimal dosing of TREO in conditioning prior to hematopoietic stem cell transplantation, especially in children. For that purpose, pharmacokinetic analyses are ongoing within clinical phase II and III trials. In this paper, HPLC methods for determination of prodrug treosulfan and/or its biologically active epoxides in human plasma or serum are reviewed for the first time, including the spectrum of analytes being quantified, detection type, and derivatization methodology. The major focus is addressed to the stability of TREO and its monoepoxide related with different strategies of patients' blood processing, e.g. blood pH lowering to different values, no pH adjustment; centrifugation of blood immediately after collection or within a few hours later. This issue is crucially important for the robust bioanalysis because the epoxytransformation of TREO is a nonenzymatic, highly pH and temperature-dependent reaction. In-depth analysis of the literature results demonstrates that some methodologies of blood treatment could produce the systematic underestimation of TREO concentrations. Consequently, the drug clearance and volume of distribution will be overestimated, which might false the association of the drug exposure with the regimen-related toxicity and clinical outcomes. The paper indicates the deficiencies of the blood processing strategies and offers hints for their refinement. The provided information ought to be important in the current investigations of the personalized TREO pharmacokinetics.