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A fully validated bioanalytical methods are prerequisite for pharmacokinetic and bioequivalence studies as well as for therapeutic drug monitoring. Due to high pharmacokinetic variability and narrow therapeutic index, vancomycin requires reliable quantification methods for therapeutic drug monitoring. To identify published chromatographic based bioanalytical methods for vancomycin in current systematic review, PubMed and ScienceDirect databases were searched. The selected records were evaluated against the method validation criteria derived from international guidelines for critical assessment. The major deficiencies were identified in method validation parameters specifically for accuracy, precision and number of calibration and validation standards, which compromised the reliability of the validated bioanalytical methods. The systematic review enacts to adapt the recommended international guidelines for suggested validation parameters to make bioanalysis reliable.

Aims The purpose of this study was to explore pharmacokinetic and pharmacodynamic aspects of a contemporary dosing scheme of cefuroxime as perioperative prophylaxis in cardiac surgery using cardiopulmonary bypass (CPB). Methods Cefuroxime plasma concentrations were measured in 23 patients. A 1.5-g dose of cefuroxime was administered at start of surgery and CPB, followed by 3 additional doses every 6 hours postoperative. Drug levels were used to build a population pharmacokinetic model. Target attainment for Staphylococcus aureus (2-8 mg/L) and Escherichia coli (8-32 mg/L) were evaluated and dosing strategies for optimization were investigated. Results A dosing scheme of 1.5 g cefuroxime preoperatively with a repetition at start of CPB achieves plasma unbound concentrations of 8 mg/L in almost all patients during surgery. The second administration is critical to provide this level of coverage. Simulations indicate that higher unbound concentrations up to 32 mg/L are reached by a continuous infusion rate of 1 g/h after a bolus of 1 g. In the postoperative phase, most patients do not reach unbound concentrations above 2 mg/L. To improve target attainment up to 8 mg/L, the continuous application of cefuroxime with infusion rates of 0.125-0.25 g/h is simulated and shown to be an alternative to bolus dosing. Conclusion Dosing recommendations for cefuroxime as perioperative antibiotic prophylaxis in cardiac surgery are sufficient to reach plasma unbound concentration to cover S. aureus during the operation. Target attainment is not achieved in the postoperative period. Continuous infusion of cefuroxime may optimize target attainment.

Aims Adequate plasma concentrations of antibiotics during surgery are essential for the prevention of surgical site infections. We examined the pharmacokinetics of 1.5 g cefuroxime administered during induction of anaesthesia with follow-up doses every 2.5 hours until the end of surgery. We built a physiologically based pharmacokinetic model with the aim to ensure adequate antibiotic plasma concentrations in a heterogeneous population. Methods A physiologically based pharmacokinetic model (PK-Sim® /MoBi® ) was developed to investigate unbound plasma concentrations of cefuroxime. Blood samples from 25 thoracic surgical patients were analysed with high-performance liquid chromatography. To evaluate optimized dosing regimens, physiologically based pharmacokinetic model simulations were conducted. Results Dosing simulations revealed that a standard dosing regimen of 1.5 g every 2.5 hours reached the pharmacokinetic/pharmacodynamic target for Staphylococcus aureus. However, for Escherichia coli, >50% of the study participants did not reach predefined targets. Effectiveness of cefuroxime against E. coli can be improved by administering a 1.5 g bolus immediately followed by a continuous infusion of 3 g cefuroxime over 3 hours. Conclusion The use of cefuroxime for perioperative antibiotic prophylaxis to prevent staphylococcal surgical site infections appears to be effective with standard dosing of 1.5 g preoperatively and follow-up doses every 2.5 hours. In contrast, if E. coli is relevant in surgeries, this dosing regimen appears insufficient. With our derived dose recommendations, we provide a solution for this issue.

We investigated covariates of pharmacokinetics of micafungin in critically ill patients. After application of micafungin, plasma samples were collected. Non-linear mixed effects modelling (NONMEM 7.3) was used to develop the pharmacokinetic model. Using this model, the adequacy of a fixed 100 mg dosing regimen was evaluated in the study cohort. A two-compartment model with linear elimination was found to describe the obtained data. SOFA score was identified as a significant covariate on both clearance and central volume of distribution, respectively. Patients in highly critical condition, represented by a SOFA above 10 showed a 30.8% lower central volume of distribution than the less critically ill patients. For patients with bilirubin levels above 4 mg/dl, clearance was decreased by 21.1%. Renal replacement therapy (RRT) did not influence micafungin clearance or the volumes of distribution. In a posthoc evaluation of the modeled population, 100 mg micafungin was suitable when assessing the PKPD targets (AUC/MIC) for C. albicans and C. glabrata, with insufficient target attainment for C. parapsilosis. Micafungin pharmacokinetics appear not to be influenced by the status of RRT. A dose of 100 mg micafungin is suitable for infections with C. albicans and C. glabrata in critically ill patients.

Background To determine the distribution of vancomycin into the cerebrospinal fluid (CSF) in patients with external ventricular drain (EVD)-associated ventriculitis, the pharmacokinetics of vancomycin were evaluated, and covariate relationships explored. Methods For the population pharmacokinetic model patients were recruited in a neuro-critical care unit at the University Hospital of Muenster in the period between January 2014 and June 2015. All patients had a clinical evidence of (EVD)-associated ventriculitis. Population pharmacokinetic analysis of vancomycin was performed using NONMEM®. Results A total of 184 blood and 133 CSF samples were collected from 29 patients. The final population pharmacokinetic model is a three-compartment model with linear elimination. Creatinine clearance (ClCr ) and CSF-lactate were detected as significant covariates, showing that the total vancomycin plasma clearance (Cl) depends on ClCr and furthermore, the clearance (Cldif ) between the central and CSF compartment correlates with CSF lactate concentration. Based on the final model, the following values were estimated by NONMEM®: Cl = 5.15 L/h, Q (intercompartmental clearance) =3.31L/h, Cldif = 0.0031 L/h, Vcentral = 42.1 L, VCSF = 0.32 L and the value of Vperipheral was fixed to 86.2 L. With the developed pharmacokinetic model, AUC (area under the curve) values as well as CSF trough levels were simulated. Conclusion Based on our analysis, the dosing of vancomycin should be referred to the degree of inflammation (derived from the CSF lactate concentration) and renal function (derived from ClCr ).

Controversy exists regarding dose adjustment in patients treated with voriconazole due to the severity of the infections for which it is prescribed. The Dutch Pharmacogenetics Working Group (DPWG) recommends a 50% dose increase or decrease for cytochrome P450 (CYP) 2C19 ultrarapid (UM) or poor (PM) metabolizers, respectively. In contrast, for the previous phenotypes, the Clinical Pharmacogenetics Implementation Consortium (CPIC) voriconazole guideline only recommends a change of treatment. Based on observed data from single-dose bioequivalence studies and steady-state observed concentrations, we aimed to investigate voriconazole dose adjustments by means of physiologically based pharmacokinetic (PBPK) modeling. PBPK modeling was used to optimize voriconazole single-dose models for each CYP2C19 phenotype, which were extrapolated to steady state and evaluated for concordance with the therapeutic range of voriconazole. Based on optimized models, dose adjustments were evaluated for better adjustment to the therapeutic range. Our models suggest that the standard dose may only be appropriate for normal metabolizers (NM), although they would benefit from a 50–100% loading dose increase. Intermediate metabolizers (IMs) and PMs required a daily dose reduction of 50 and 75%, respectively. Rapid metabolizers (RMs) and UMs required a daily dose increase of 100% and 300%, respectively. The prescription of voriconazole in clinical practice should be personalized according to the CYP2C19 phenotype, followed by therapeutic drug monitoring of plasma concentrations to guide dose adjustment.

Aspergillus galactomannan antigenemia is an accepted tool for the diagnosis of invasive pulmonary aspergillosis (IPA) in neutropenic patients. Little is known, however, about the utility of this biomarker to assess the efficacy of antifungal therapies. The pharmacokinetics (PK) and pharmacodynamics (PD) of posaconazole in treatment and prophylaxis were investigated in the persistently neutropenic rabbit model of Aspergillus fumigatus IPA at doses between 2 and 20 mg/kg per day. Sparse plasma sampling was used to obtain PK data at steady state, and the serum galactomannan index (GMI), as a dynamic endpoint of antifungal response, was obtained every other day, in addition to conventional outcome parameters including survival and fungal tissue burden. Nonparametric PK/PD model building was performed using the Pmetrics package in R. A one-compartment model with linear elimination best described the PK of posaconazole. The PD effect of posaconazole exposure in plasma on the GMI in serum was best described by dynamic Hill functions reflecting growth and killing of the fungus. Through calculations of the area under the concentration-time curve from 0 to 24 h (AUC(0–24)) at steady state, the exposure-response relationship between posaconazole and the GMI for treatment followed a sigmoidal function with an asymptote forming above an AUC(0–24) of 30 mg · h/liter. All prophylactic doses were able to control the fungal burden. A nonparametric population PK/PD model adequately described the effect of posaconazole in prophylaxis and treatment of experimental IPA. An AUC(0–24) greater than 30 mg · h/liter was associated with adequate resolution of the GMI, which well supports previously suggested exposure-response relationships in humans.

Purpose Dose-optimization strategies for risperidone are gaining in importance, especially in the elderly. Based on the genetic polymorphism of cytochrome P 450 (CYP) 2D6 genetically and age-related changes cause differences in the pharmacokinetics of risperidone and 9-hydroxyrisperidone. The goal of the study was to develop physiologically based pharmacokinetic (PBPK) models for the elderly aged 65+ years. Additionally, CYP2D6 phenotyping using metabolic ratio were applied and different pharmacokinetic parameter for different age classes predicted. Methods Plasma concentrations of risperidone and 9-hydroxyrisperidone were used to phenotype 17 geriatric inpatients treated under naturalistic conditions. For this purpose, PBPK models were developed to examine age-related changes in the pharmacokinetics between CYP2D6 extensive metabolizer, intermediate metabolizer, poor metabolizer, (PM) and ultra-rapid metabolizer. Results PBPK-based metabolic ratio was able to predict different CYP2D6 phenotypes during steady-state. One inpatient was identified as a potential PM, showing a metabolic ratio of 3.39. About 88.2% of all predicted plasma concentrations of the inpatients were within the 2-fold error range. Overall, age-related changes of the pharmacokinetics in the elderly were mainly observed in Cmax and AUC. Comparing a population of young adults with the oldest-old, Cmax of risperidone increased with 24–44% and for 9-hydroxyrisperidone with 35–37%. Conclusions Metabolic ratio combined with PBPK modelling can provide a powerful tool to identify potential CYP2D6 PM during therapeutic drug monitoring. Based on genetic, anatomical and physiological changes during aging, PBPK models ultimately support decision-making regarding dose-optimization strategies to ensure the best therapy for each patient over the age of 65 years.

Background Despite its cardiotoxicity doxorubicin is widely used for the treatment of paediatric malignancies. Current treatment regimens appear to be suboptimal as treatment strategies vary and do not follow a clear pharmacological rationale. Standardisation of dosing strategies in particular for infants and younger children is required but is hampered by scarcely defined exposure-response relationships. The aim is to provide a rational dosing concept allowing for a reduction of variability in systemic therapy intensity and subsequently unforeseen side effects. Methods Doxorubicin plasma concentrations in paediatric cancer patients were simulated for different treatment schedules using a population pharmacokinetic model which considers age-dependent differences in doxorubicin clearance. Overall drug exposure and peak concentrations were assessed. Simulation results were used to support a three round Delphi consensus procedure with the aim to clarify the pharmacological goals of doxorubicin dosing in young children. A group of 28 experts representing paediatric trial groups and clinical centres were invited to participate in this process. Results Pharmacokinetic simulations illustrated the substantial differences in therapy intensity associated with current dosing strategies. Consensus among the panel members was obtained on a standardised a priori dose adaptation that individualises doxorubicin doses based on age and body surface area targeting uniform drug exposure across children treated with the same protocol. Further, a reduction of peak concentrations in very young children by prolonged infusion was recommended. Conclusions An approach to standardise current dose modification schemes in young children is proposed. The consented concept takes individual pharmacokinetic characteristics into account and involves adaptation of both the dose and the infusion duration potentially improving the safety of doxorubicin administration.

Anticancer drugs are good candidates for therapeutic drug monitoring (TDM) because of their high toxicity and documented exposure–response relationship for many anticancer drugs. In contrast to this, a few years ago Peterson concluded that in oncology “…plasma concentration monitoring has not proved to be of value to individualize the treatment…”. However, there are several examples where TDM in oncology has been shown to improve safety, and for some drugs, also efficacy. Examples such as 5-fluorouracil, busulfan, asparaginase, or imatinib are discussed below. It appears that there is a lack of interest of TDM and other pharmacokinetic issues in cancer chemotherapy. There is the perception that in case of toxicity or lack of efficacy switching to another drug is better than checking dose intensity of the drug applied. However, dose individualisation based on drug concentration measurements has been shown to be advantegeous for many anticancer agents.

Background and Objectives: Doxorubicin plays an essential role in the treatment of paediatric cancers. Defining genotypes with a higher risk for developing anthracycline-induced cardiotoxicity could help to reduce cardiotoxicity. Methods: Data originated from a phase II study assessing the pharmacokinetics of doxorubicin in 100 children. Studied patients (0–17 years) were treated for solid tumours or leukaemia. Two cycles of doxorubicin were studied. Concentrations of natriuretic peptides proANP, BNP and NT-proBNP and cardiac troponins T and I were measured at five time points before, during and after two cycles of doxorubicin treatment. Genotypes of 17 genetic polymorphisms in genes encoding for anthracycline metabolizing enzymes and drug transporters were determined for each patient. We analysed the influence of genotypes on cardiac biomarker concentrations at different time points by a Kruskal–Wallis test. To perform a pairwise comparison significant genetic polymorphisms with more than two genotypes were analysed by a post hoc test. Results: The Kruskal–Wallis tests and the post hoc-tests showed a significant association for seven genetic polymorphisms (ABCB1-rs1128503, ABCB1-rs1045642, ABCC1-rs4148350, CBR3-rs8133052, NQO2-in/del, SLC22A16-rs714368 and SLC22A16-rs6907567) with the concentration of at least one biomarker at one or more time points. We could not identify any polymorphism with a consistent effect on any biomarker over the whole treatment period. Conclusions: In this study of patients treated with doxorubicin for different tumour entities, seven genetic polymorphisms possibly influencing the pharmacokinetics and pharmacodynamics of doxorubicin could lead occasionally to differences in the concentration of cardiac biomarkers. Since, the role of cardiac biomarkers for monitoring anthracycline-induced cardiotoxicity has not yet been clarified, further trials with a long follow-up time are required to assess the impact of these genetic polymorphisms on chemotherapy-related cardiotoxicity. Trial registration: EudraCT number: 2009-011454-17. Refereed/Peer-reviewed

The objective of this study was to assess the pharmacokinetics of recombinant asparaginase (rASNase, Spectrila®) in children with acute lymphoblastic leukemia using a population pharmacokinetic approach in order to explore potential dosing recommendations. Data on serum asparaginase activities of 124 children from three clinical studies were included in the analysis, covering an age range from 3 days to 17 years. Most patients received 5000 U/m2 rASNase intravenously every 3 days. The non-linear mixed effects modelling software (NONMEM®) was utilized to identify drivers of rASNase pharmacokinetics in children. Different dose adjustments were simulated for their ability to increase rASNase trough activities in children who do not reach the threshold of 100 U/L. A two-compartment model with allometric weight scaling (0.75 on clearance [CL] and inter-compartmental clearance [Q] and 1 on central [V 1] and peripheral [V 2] volume of distribution) was the best model to describe the pharmacokinetics of rASNase. PK parameters for the median child (19.5 kg) were: CL = 0.0592 L/h, V 1 = 1.18 L, Q = 0.307 L/h, V 2 = 0.316 L. Organ functions, such as liver or kidney function and laboratory values, such as fibrinogen or antithrombin III levels, showed no influence on rASNase pharmacokinetics. In simulations, changing the administration interval from 72 to 48 h was appropriate to maintain rASNase activities above the therapeutic threshold, in patients with activities below 100 U/L 72 h after the first dose. Drug monitoring is recommended to identify patients with insufficient ASNase trough activities in serum and to modify the treatment schedule, if necessary. Shortening of the treatment interval might be preferable over increasing the rASNase dose.

Since pregnant women are considerably underrepresented in clinical trials, information on optimal dosing in pregnancy is widely lacking. Physiologically based pharmacokinetic (PBPK) modeling may provide a method for predicting pharmacokinetic changes in pregnancy to guide subsequent in vivo pharmacokinetic trials in pregnant women, minimizing associated risks. The goal of this study was to build and verify a population PBPK model that predicts the maternal pharmacokinetics of three predominantly renally cleared drugs (namely cefazolin, cefuroxime, and cefradine) at different stages of pregnancy. It was further evaluated whether the fraction unbound (f u) could be estimated in pregnant women using a proposed scaling approach. Based on a recent literature review on anatomical and physiological changes during pregnancy, a pregnancy population PBPK model was built using the software PK-Sim®/MoBi®. This model comprised 27 compartments, including nine pregnancy-specific compartments. The PBPK model was verified by comparing the predicted maternal pharmacokinetics of cefazolin, cefuroxime, and cefradine with observed in vivo data taken from the literature. The proposed scaling approach for estimating the f u in pregnancy was evaluated by comparing the predicted f u with experimentally observed f u values of 32 drugs taken from the literature. The pregnancy population PBPK model successfully predicted the pharmacokinetics of cefazolin, cefuroxime, and cefradine at all tested stages of pregnancy. All predicted plasma concentrations fell within a 2-fold error range and 85% of the predicted concentrations within a 1.25-fold error range. The f u in pregnancy could be adequately predicted using the proposed scaling approach, although a slight underestimation was evident in case of drugs bound to α1-acidic glycoprotein. Pregnancy population PBPK models can provide a valuable tool to predict a priori the pharmacokinetics of predominantly renally cleared drugs in pregnant women. These models can ultimately support informed decision making regarding optimal dosing regimens in this vulnerable special population

Sepsis is characterised by an excessive release of inflammatory mediators substantially affecting body composition and physiology, which can be further affected by intensive care management. Consequently, drug pharmacokinetics can be substantially altered. This study aimed to extend a whole-body physiologically based pharmacokinetic (PBPK) model for healthy adults based on disease-related physiological changes of critically ill septic patients and to evaluate the accuracy of this PBPK model using vancomycin as a clinically relevant drug. The literature was searched for relevant information on physiological changes in critically ill patients with sepsis, severe sepsis and septic shock. Consolidated information was incorporated into a validated PBPK vancomycin model for healthy adults. In addition, the model was further individualised based on patient data from a study including ten septic patients treated with intravenous vancomycin. Models were evaluated comparing predicted concentrations with observed patient concentration–time data. The literature-based PBPK model correctly predicted pharmacokinetic changes and observed plasma concentrations especially for the distribution phase as a result of a consideration of interstitial water accumulation. Incorporation of disease-related changes improved the model prediction from 55 to 88% within a threshold of 30% variability of predicted vs. observed concentrations. In particular, the consideration of individualised creatinine clearance data, which were highly variable in this patient population, had an influence on model performance. PBPK modelling incorporating literature data and individual patient data is able to correctly predict vancomycin pharmacokinetics in septic patients. This study therefore provides essential key parameters for further development of PBPK models and dose optimisation strategies in critically ill patients with sepsis.

Background In the context of the cholinergic anti-inflammatory pathway, the clinical trial Anticholium® per Se (EudraCT Number: 2012-001650-26, ClinicalTrials.gov NCT03013322) addressed the possibility of taking adjunctive physostigmine salicylate treatment in septic shock from bench to bedside. Pharmacokinetics (PK) are likely altered in critically ill patients; data on physostigmine PK and target concentrations are sparse, particularly for continuous infusion. Our objective was to build a population PK (popPK) model for physostigmine, and further evaluate pharmacodynamics (PD) and concentration-response relationship in this setting. Methods In the randomized, double-blind, placebo-controlled trial, 20 patients with perioperative septic shock either received an initial dose of 0.04 mg/kg physostigmine salicylate, followed by continuous infusion of 1 mg/h for up to 120 h, or equivalent volumes of 0.9% sodium chloride (placebo group). Physostigmine plasma concentrations and acetylcholinesterase (AChE) activity were measured; concentration-response associations were evaluated, and popPK and PD modeling was performed with NONMEM. Results Steady state physostigmine plasma concentrations reached 7.60 ± 2.81 ng/mL (mean ± standard deviation [SD]). PK was best described by a two-compartment model with linear clearance. Significant covariate effects were detected for body weight and age on clearance, as well as a high inter-individual variability of the central volume of distribution. AChE activity was significantly reduced to 30.5%–50.6% of baseline activity during physostigmine salicylate infusion. A sigmoidal direct effect PD model best described enzyme inhibition by physostigmine, with an estimated half maximal effective concentration (EC50) of 5.99 ng/mL. Conclusions PK of physostigmine in patients with septic shock displayed substantial inter-individual variability with body weight and age influencing the clearance. Physostigmine inhibited AChE activity with a sigmoidal concentration-response effect.

The genetic polymorphism of cytochrome P450 (CYP) 2D6 is characterized by an excessive impact on positive and adverse drug reactions to antipsychotics, such as risperidone. Consequently, the pharmacokinetics of the drug and metabolite can be substantially altered and exhibit a high variability between the different phenotypes. The goal of this study was to develop a physiologically based pharmacokinetic (PBPK) model considering the CYP2D6 genetic polymorphism for risperidone and 9-hydroxyrisperidone (9-OH-RIS) taking CYP3A4 into account. Additionally, risperidone dose adjustments, which would compensate for genetically caused differences in the plasma concentrations of the active moiety (sum of risperidone and 9-OH-RIS) were calculated. Based on available knowledge about risperidone, 9-OH-RIS, and relevant physiological changes according to different CYP2D6 phenotypes, several PBPK models were built. In addition, an initial model was further evaluated based on the plasma concentrations of risperidone and 9-OH-RIS from a single-dose study including 71 genotyped healthy volunteers treated with 1 mg of oral risperidone. PBPK models were able to accurately describe risperidone exposure after single-dose administration, especially in the concentration range ≥ 1 µg/L, illustrated by a minimal bias and a good precision. About 90.3% of all weighted residuals versus observed plasma concentrations ≥ 1 µg/L were in the ± 30% range. The risperidone/9-OH-RIS ratio increased progressively according to reduced CYP2D6 activity, resulting in a mean ratio of 4.96 for poor metabolizers. Simulations demonstrate that dose adjustment of the drug by − 25% for poor metabolizers and by – 10% for intermediate metabolizers results in a similar exposure to that of extensive metabolizers. Conversely, the risperidone/9-OH-RIS ratio can be used to determine the phenotype of individuals. PBPK modelling can provide a valuable tool to predict the pharmacokinetics of risperidone and 9-OH-RIS in healthy volunteers, according to the different CYP2D6 phenotypes taking CYP3A4 into account. These models are able to ultimately support decision-making regarding dose-optimization strategies, especially for subjects showing lower CYP2D6 activity.

Purpose The aim of this study was to evaluate the influence of age and other possible covariates on vancomycin clearance in order to define a possible cut off value of age for dose optimization in elderly patients from data obtained during therapeutic drug monitoring. Materials and methods Population pharmacokinetic analysis of 256 samples obtained from 144 patients was performed by using NONMEM®. A one-compartment model was applied as the base model with first-order conditional estimation method with interaction (FOCE-I). The influence of different covariates was investigated by stepwise covariate modeling, and the final model was evaluated by goodness-of-fit plots and bootstrap analysis using 1,000 datasets. Results In the final model, the mean values for vancomycin clearance (CL) and volume of distribution (VD) were 2.32 L/h and 19.2 L, respectively. Vancomycin CL was significantly influenced by creatinine CL (CLCR) in a stepwise covariate modeling, and it was lowest in patients of 75 years and above when compared with other age groups. Conclusion Vancomycin CL decreases progressively with increasing age due to the reduction in CLCR in older patients. Therefore, dose adjustment should be based on CLCR for safe use of vancomycin in patients ≥ 75 years of age or older. .

Invasive fungal infections are recognized as life-threatening complications primarily in immunocompromised patients, including children with primary immunodeficiencies and hematological malignancies. The antifungal triazoles have become extremely useful components of the antifungal armamentarium. They are well tolerated and possess a broad spectrum of activity. Itraconazole was discovered in 1984 and became available for clinical use in 1990. Itraconazole is a broad spectrum, triazole antifungal agent, and class II drug molecule with low solubility and high permeability and several indications in adults. This article provides a brief overview of the pharmacology of itraconazole with focus on the available data in immunocompromised children and adolescents.

Physiologically based pharmacokinetic modeling is considered a valuable tool for predicting pharmacokinetic changes in pregnancy to subsequently guide in-vivo pharmacokinetic trials in pregnant women. The objective of this study was to extend and verify a previously developed physiologically based pharmacokinetic model for pregnant women for the prediction of pharmacokinetics of drugs metabolized via several cytochrome P450 enzymes. Quantitative information on gestation-specific changes in enzyme activity available in the literature was incorporated in a pregnancy physiologically based pharmacokinetic model and the pharmacokinetics of eight drugs metabolized via one or multiple cytochrome P450 enzymes was predicted. The tested drugs were caffeine, midazolam, nifedipine, metoprolol, ondansetron, granisetron, diazepam, and metronidazole. Pharmacokinetic predictions were evaluated by comparison with in-vivo pharmacokinetic data obtained from the literature. The pregnancy physiologically based pharmacokinetic model successfully predicted the pharmacokinetics of all tested drugs. The observed pregnancy-induced pharmacokinetic changes were qualitatively and quantitatively reasonably well predicted for all drugs. Ninety-seven percent of the mean plasma concentrations predicted in pregnant women fell within a twofold error range and 63% within a 1.25-fold error range. For all drugs, the predicted area under the concentration–time curve was within a 1.25-fold error range. The presented pregnancy physiologically based pharmacokinetic model can quantitatively predict the pharmacokinetics of drugs that are metabolized via one or multiple cytochrome P450 enzymes by integrating prior knowledge of the pregnancy-related effect on these enzymes. This pregnancy physiologically based pharmacokinetic model may thus be used to identify potential exposure changes in pregnant women a priori and to eventually support informed decision making when clinical trials are designed in this special population.

Introduction Tamoxifen is one of the most common treatment opportunities for hormonal positive breast cancer. Despite its good tolerability, patients demonstrate decreasing adherence over years impacting on therapeutic success. PBPK modeling was applied to demonstrate the impact of drug holidays on plasma levels of tamoxifen and its active metabolite endoxifen for different CYP2D6 genotypes. Materials and Methods A virtual study with 24,000 patients was conducted in order to investigate the development of tamoxifen steady-state kinetics in patient groups of different CYP2D6 genotypes. The impact of drug holidays on steady-state kinetics was investigated assuming changing drug holiday scenarios. Results Drug holidays in CYP2D6 extensive and intermediate metabolizers (EMs, IMs) exceeding one month lead to a decrease of endoxifen steady-state trough levels below the 5th percentile of the control group. Assuming drug holidays of one, two, or three months and administering a fixed-dose combination of 20 mg tamoxifen and 3 mg endoxifen EMs demonstrated re-established endoxifen steady-state trough levels after 5, 8, and 9 days. IMs receiving the same fixed-dose combination demonstrated re-established endoxifen steady-state trough levels after 7, 10, and 11 days. Discussion The PBPK model impressively demonstrates the impact of drug holidays in different CYP2D6 genotypes on PK. Population simulation results indicate that drug holidays of more than two weeks cause a tremendous decrease of plasma levels despite the long half-life of tamoxifen. To improve therapeutic success, PBPK modeling allows identifying genotype-specific differences in PK following drug holidays and adequate treatment with loading doses.

We evaluated the patterns and determinants that influence the selection, timing and duration of first-line antihyperglycaemic drug (AHD) treatment in patients with type 2 diabetes in Germany, focusing specifically on treatment-naive AHD initiators.Pharmacy dispensing claims data were linked with a cohort of patients newly enrolled in a German Disease Management Program for type 2 diabetes (DMP-DM2) between 2003 and 2009. We examined uptake of first-line pharmacotherapy in previously unmedicated patients and identified predictors of receiving AHD therapy in general and metformin in particular using multivariable regression analyses.There were 27,138 unmedicated patients with type 2 diabetes and 47.0% of them were started on AHD treatment within 5 years after enrollment. Initial severity of diabetes was the major predictor of receiving first-line pharmacotherapy. Metformin accounted for 63% of newly prescribed AHD in 2003 and more than 80% in 2009 while sulfonylureas accounted for only 10%. Initiating metformin as first-line AHD was associated with younger age, higher BMI, lower HbA1c, and shorter diabetes duration (multivariate p0.001 for all). Therapy switch or step-up was less frequent among metformin initiators than sulfonylurea initiators.The majority of patients were not started on AHD therapy within 5 years after enrollment. In line with recent therapy guidelines, current first-line antihyperglycaemic treatment was increasingly based on metformin. AHD initiators started on sulfonylurea were generally more advanced in their disease and were started later on primary pharmacotherapy.

We developed a new population pharmacokinetic (PopPK) model for intravenous (i.v.) busulfan in children to evaluate the optimal method to personalize its dosing without concentration-time data.PopPK analyses were done with NONMEM® 7.2. First, a model from Trame et al. was evaluated using an external dataset consisting of 24 children. Second, a revised model was built in a separate dataset of 82 children. Model evaluation was performed by using a standardized visual predictive check (SVPC) procedure and a bootstrap analysis (internal evaluation) and by comparison to an external dataset (external validation).The final model included body surface area (BSA) as an exponential function on volume of distribution (V) and actual body weight (ABW) as an allometric function on clearance (CL). The dosing nomogram for every 6 h administration derived from the final model is: dose[mg]=target AUC[mg×h/L]×3.04L/h×(ABW/16.1)0.797. Compared to other dosing strategies, differences were observed for the very small and obese patients.We revised our prior dosing nomogram after validation in a separate cohort of children. This dosing nomogram can be used to personalize i.v. busulfan doses without concentration-time data, but an additional prospective evaluation in the very small and obese children is needed.

Background Busulfan (Bu) is a DNA-alkylating agent used for myeloablative conditioning in stem cell transplantation in children and adults. While the use of intravenous rather than oral administration of Bu has reduced inter-individual variability in plasma levels, toxicity still occurs frequently after hematopoietic stem cell transplantation (HSCT). Toxicity (especially hepatotoxic effects) of intravenous (IV) Bu may be related to both Bu and/or N,N-dimethylacetamide (DMA), the solvent of Bu. In this study, we assessed the relation between the exposure of Bu and DMA with regards to the clinical outcome in children from two cohorts. Methods In a two-centre study Bu and DMA AUC (area under the curve) were correlated in pediatric stem cell recipients to the risk of developing SOS and to the clinical outcome. Result In patients receiving Bu four times per day Bu levels >1,500 µmol/L minute correlate to an increased risk of developing a SOS. In the collective cohort, summarizing data of all 53 patients of this study, neither high area under the curve (AUC) of Bu nor high AUC of DMA appears to be an independent risk factor for the development of SOS in children. Conclusion In this study neither Bu nor DMA was observed as an independent risk factor for the development of SOS. To identify subgroups (e.g., infants), in which Bu or DMA might be risk factors for the induction of SOS, larger cohorts have to be evaluated. Pediatr Blood Cancer 2014;61:306–311. © 2013 Wiley Periodicals, Inc.

Purpose: N,N-dimethylacetamide (DMA) is administered to children during high-dose chemotherapy as a solubilizer with the intravenous formulation of busulfan (Busilvex®). DMA has shown liver toxicity in rats. However, little is known regarding its pharmacokinetics (PK) in humans. The aim of this analysis was to compare the PK of DMA after a once-daily dose of Busilvex® with the standard scheme consisting of 3-4 administrations per day in children. Methods: Out of 42 children, aged 0.1-18.9 years, receiving Busilvex®, 18 children received the first dose as a loading dose, giving a double dose of 1.4-2.0 mg/kg over a 4 h infusion followed by 15 doses of 0.7-1.0 mg/kg as 2 h infusions every 6 h. The other 24 children received Busilvex® as 3 h infusions once-daily for 4 consecutive days with a targeted busulfan AUC of 4,263 μM*min. Using NONMEM™ plasma, concentration-time data were analyzed. Assuming an increase in clearance overtime as found in our previous investigation, separate time factors for the two different dosing schedules included in the dataset were tested. Results: A one-compartment model with clearance increasing over time described the DMA kinetics sufficiently. Peak plasma concentrations of DMA, up to 3.09 mmoL/L (median 0.75 mmoL/L) for the current licensed dose regimen and up to 8.77 mmoL/L (median 3 mmoL/L) for the once-daily application, were observed. The examined increase in clearance was found to be 58 mL/h/kg and 6.1 mL/h/kg per day for the current licensed and the once-daily dose regimen, respectively. Conclusion: N,N-dimethylacetamide as solvent of lipophilic drugs such as busulfan has a linear PK in children of all ages using a dose split into one or four administrations per day. The rapid clearance with different dosing in patients of different body weights indicates that it is safe to use DMA in children in both a once and four times daily regimen.

A physiologically based pharmacokinetic (PBPK) model was established and evaluated describing the pharmacokinetics (PK) of the DNA-alkylating agent Busulfan in adults in order to predict the systemic Busulfan drug exposure in both plasma and toxicity-related organs. A generic PBPK model was tailored to describe Busulfan PK by implementing compound-specific physicochemical and metabolism data. With regard to possible influences of glutathione S transferase (GST) variations on Busulfan PK, two different PBPK model parameterizations were investigated: a first parameterization with individual GST activity (expressed as different estimated V max values) for each patient, and a resulting second model parameterization with a mean GST activity for all patients. Simulations were computed and compared to concentration–time data after intravenous Busulfan administration to 108 adults serving as development dataset. Subsequently, appropriateness of the PBPK model was evaluated with an external dataset not used for model development, consisting of 95 adults. Both PBPK model parameterizations of Busulfan successfully described the observed plasma concentrations. For the validation dataset, calculated PK parameters were as follows: clearance 0.16 ± 0.03 L/h/kg and volume of distribution 0.65 ± 0.06 L/kg (mean ± standard deviation). Mean absolute percentage error was less than 30 % for each PK parameter. Mass balances for distribution and excretion were in good agreement with the literature data. Both PBPK model parameterizations sufficiently described the observed concentration–time data while showing an adequate predictive performance. The model should be further evaluated for its ability to explain the between-subject variability in intravenous Busulfan PK parameters.

Citalopram, mirtazapine and risperidone are frequently prescribed for psychiatric illnesses such as depression and psychosis or for aggressive behavior in elderly patients with dementia. The plasma concentrations vary greatly between patients, especially in elderly patients. Thus, therapeutic drug monitoring (TDM) increases the safety of antipsychotic treatment and a more rapid response to treatment may be achieved. To facilitate TDM, the objectives of this study were to develop and validate a reliable dried blood spot method to simultaneously quantify citalopram, mirtazapine and risperidone including its active metabolite 9-hydroxyrisperidone. The blood punches were extracted by methanol using an ultrasonic bath, purified by liquid-liquid extraction and analyzed by liquid chromatography/mass spectrometry (LC-MS). All acceptance criteria of the EMA and FDA guidelines for method validation were fulfilled. Linearity was shown over the range of 2.5-300μg/L for all substances. The analytes were stable for at least one month at all investigated storage conditions, including storing at room temperature exposed to light. Retrieving capillary blood by finger-pricking the assay was successfully applied in elderly patients. Venous serum samples were drawn simultaneously to compare capillary blood with serum concentrations. Given the validated results and the calculated capillary blood:serum ratio, the studied dried blood spot method offers an excellent application in TDM and can be applied in ambulatory care.

The aim of this study was to evaluate different dosage regimens of meropenem in elderly patients in relation with renal function using a population pharmacokinetic (popPK) model. The data of 178 elderly patients treated with meropenem was collected from different sources. A popPK model was developed by using NONMEM® and the influence of different covariates on meropenem CL and V1 was observed. Monte Carlo dosing simulations were performed at steady state to observe the % T > MIC for targets of 40, 60 and 80% of dosage intervals at different levels of creatinine clearance (CLCR). The data was described by a two-compartment model and the values of parameter estimates for CL, V1, Q and V2 were 5.27 L/h, 17.2 L, 9.92 L/h and 10.6 L, respectively. The CLCR, body weight and centre had a significant influence on meropenem CL while no direct influence of age was observed. Extended infusions had pharmacokinetic and pharmacodynamic (PK/PD) breakpoint one dilution greater than corresponding short infusion regimens for each target of % T > MIC. Meropenem CL was significantly lower in the elderly compared to CL reported in younger patients due to the reduced renal function. An extended infusion of 1000 mg q8h can be considered for empirical treatment of infections in elderly patients when CLCR is ≤ 50 mL/min. A continuous infusion of 3000 mg daily dose is preferred if CLCR > 50 mL/min. However, a higher daily dose of meropenem would be required for resistant strains (MIC >8 mg/L) of bacteria if CLCR is >100 mL/min.

Adequate levels of perioperative antibiotic prophylaxis are essential for prevention of surgical site infections. We examined pharmacokinetic details of 2 g cefazolin administered during induction of anesthesia with repeat dosing shortly after initiation of cardiopulmonary bypass (CPB) in cardiac surgery.To identify the microbiologic flora targeted with prophylaxis, pre-, and postoperative swabs were taken from sternal skin. Blood samples for measurement of cefazolin were obtained in 24 patients. Drug levels were used for population pharmacokinetic modeling using Nonmem software (Icon Development Solutions, San Antonio, Tex).More than 90% of bacteria on sternal skin were sensitive to cefazolin, indicating minimal inhibitory concentrations8 mg/L. All serum levels of cefazolin were above 8 mg/L and might thus effectively prevent infection. Pharmacokinetic modeling in a 1-compartment model predicted a population mean clearance (CL) of 5.23 L/h and a volume of distribution (Vd) of 15.8 L. CPB increased Vd from 14.4 L to 22.1 L with a consecutive reduction to 18 L after the end of extracorporeal circulation. The final model implemented interindividual variability on CL and Vd, incorporating the covariates CPB and albumin on Vd and creatinine clearance on CL. Goodness-of-fit calculations showed that this model adequately describes the data derived from our clinical cohort.Two grams of cefazolin at induction of anesthesia with a repeat dose after initiation of CPB ensures adequate drug levels to target a majority of pathogens of surgical site infections. Pharmacokinetic modeling demonstrated a significant influence of CPB on the volume of distribution and elimination of cefazolin. Other influences on pharmacokinetic parameters were albumin, protein, and creatinine clearance.

Purpose Doxorubicin is a key component in many pediatric oncology treatment regimens; still pharmacology data on which current dosing regimens are based are very limited. Methods We conducted a multinational pharmacokinetic study investigating age dependency of doxorubicin metabolism and elimination in children with cancer. One hundred and one patients treated with doxorubicin according to a cancer-specific national or European therapeutic trial were recruited. Doses of doxorubicin ranged from 10.4 to 57.7 mg/m2. Blood samples for measurement of doxorubicin and its metabolite doxorubicinol were collected after two administrations, with five samples collected in children

Liposomal amphotericin B (LAMB) and caspofungin (CAS) are important antifungal agents in allogeneic hematopoietic stem cell transplant (aHSCT) recipients. Little is known, however, about the pharmacokinetics (PK) of both agents and their combination in this population. The PK of LAMB and CAS and the potential for PK interactions between both agents were investigated within a risk-stratified, randomized phase II clinical trial in 53 adult aHSCT recipients with granulocytopenia and refractory fever. Patients received either LAMB ( n = 17; 3 mg/kg once a day [QD]), CAS ( n = 19; 50 mg QD; day 1, 70 mg), or the combination of both (CAS-LAMB; n = 17) for a median duration of 10 to 13 days (range, 4 to 28 days) until defervescence and granulocyte recovery. PK sampling was performed on days 1 and 4. Drug concentrations in plasma (LAMB, 405 samples; CAS, 458 samples) were quantified by high-pressure liquid chromatography and were analyzed using population pharmacokinetic modeling. CAS concentration data best fitted a two-compartment model with a proportional error model and interindividual variability (IIV) for clearance (CL) and central volume of distribution ( V 1 ) (CL, 0.462 liter/h ± 25%; V 1 , 8.33 liters ± 29%; intercompartmental clearance [ Q ], 1.25 liters/h; peripheral volume of distribution [ V 2 ], 3.59 liters). Concentration data for LAMB best fitted a two-compartment model with a proportional error model and IIV for all parameters (CL, 1.22 liters/h ± 64%; V 1 , 19.2 liters ± 38%; Q , 2.18 liters/h ± 47%; V 2 , 52.8 liters ± 84%). Internal model validation showed predictability and robustness of both models. None of the covariates tested (LAMB or CAS comedication, gender, body weight, age, body surface area, serum bilirubin, and creatinine clearance) further improved the models. In summary, the disposition of LAMB and CAS was best described by two-compartment models. Drug exposures in aHSCT patients were comparable to those in other populations, and no PK interactions were observed between the two compounds.

To evaluate the ability of a physiology-based pharmacokinetic (PBPK) model to predict the systemic drug exposure of high- and low-dose etoposide in children from a model developed with adult data.Simulations were performed with PK-Sim(®) (Bayer Technology Services). Model development was done using data from adult patients receiving etoposide in a conventional and high-dose polychemotherapy regimen before stem cell transplantation. Michaelis-Menten parameters from in vitro experiments reported in the literature were applied to describe the metabolism and excretion processes by P450 enzymes and transporters. The model was scaled down to children and compared to etoposide plasma concentrations in this age group.Simulated plasma concentration-time courses of protein-bound and free etoposide in adults for high- and low-dose schedules agreed with the observed data. Mean simulated total clearance of high- and low-dose etoposide was 0.70 ml/min/kg (Cl(observed): 0.70 ml/min/kg) versus 0.50 ml/min/kg (Cl(observed): 0.60 ml/min/kg), respectively. Integrated Michaelis-Menten kinetics was adequately transformed to age-related pharmacokinetics in children. Predictions of the pharmacokinetics in different age groups were also in good agreement with observed data. Drug interactions triggered by P-glycoprotein inhibitors or nephrotoxic drugs can also be elucidated.The PBPK model matched the pharmacokinetics in different dosing regimens in adults. Furthermore, the scaling procedure from the adult model to children provides useful predictions for paediatric patients. Comedication with drugs influencing the metabolism and excretion has to be taken into account. This approach could be useful for planning pharmacokinetic studies in children.

showing a trend towards a lower doxorubicin clearance in infants in comparison to children [9]. This observation could serve as a rationale for dose reduction in infants. Another reason for dose reductions in infants can be differences in the pharmacodynamics, that is, a higher cardiotoxicity or myelotoxicity in infants compared to other children when achieving the same cumulative dose of anthracyclines. In fact, younger age is an independent risk factor for the development of congestive heart failure in patients receiving anthracyclines [3]. Regarding myelotoxicity, an investigation on the pharmacokinetics of etoposide in infants showed reduced toxicity in patient receiving the drug with dose reduction to 2/3 of the body surface area (BSA)-based dose. Notably, this investigation did not show differences in the clearance of etoposide between infants and older children [10]. In the Interfant 99 protocol for the treatment of Background. There is an extreme paucity of pharmacokinetic data for anticancer agents in infants. Therefore, we aimed at characterizing the pharmacokinetics for daunorubicin in infants and examined their relationship to age, body weight, and body surface area. Procedure. Leukemia patients treated according to the Interfant 99 protocol received 30 mg/m 2 daunorubicin, with dose reduction to 3/4 for patients 6–12 months old and 2/3 for patients

The objective of the study was to assess individual distribution of antineoplastic drugs into the tumor. Twelve advanced-stage primary breast cancer patients with neoadjuvant epirubicin+paclitaxel chemotherapy were studied. Plasma concentrations of epirubicin and paclitaxel were monitored for 24 h. Epirubicin concentrations in subcutaneous and tumor tissues were measured using microdialysis up to 12 h postdose. Epirubicin concentrations were described by a compartmental population pharmacokinetic model (NONMEM). Noncompartmental analysis was used for paclitaxel. Plasma pharmacokinetics corresponded to published data. Mean epirubicin exposure in the tumor and in subcutaneous tissue was very similar, but tissue Cmax and area under the curve values reached only (means) 1% and 11%, respectively, of plasma values. Epirubicin doses were significantly correlated to tumor exposure irrespective of body surface area. There is no specific barrier for epirubicin to reach primary breast cancer tumors.

The BEACOPP (bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine and prednisone) chemotherapy regimen for the treatment of advanced Hodgkin’s lymphoma has a superior outcome, but its toxicity (mainly haematotoxicity) is pronounced and highly variable. The present study was conducted to address the role of pharmacokinetics in individual toxicity. Three plasma samples and a 24-hour urine collection for day 1 of the first three cycles of chemotherapy were analysed in 30 patients, and the pharmacokinetic parameters of the respective drugs were estimated by population pharmacokinetic methods (nonlinear mixed-effects model [NONMEM] software). Demographic data, doses and durations of infusion were also recorded. The effect of these parameters on platelet counts was estimated by analysis of covariance using a general linear model. The pharmacokinetic parameters and respective covariates were similar to the published data. The body surface area, peak concentrations of etoposide, urinary recovery of dechloroethylcyclophosphamide (formed by cytochrome P450 [CYP] 3A4) relative to the cyclophosphamide dose and number of cycles had a significant effect on toxicity. These factors explained 37% of the interindividual variability in the change in platelet counts from day 1 to day 8 of each cycle. The results show that the individual pharmacokinetics of BEACOPP drugs are an important link between dosage and toxicity. Accordingly, individualisation of treatment based on pharmacokinetics may result in more uniform toxicity. Individualisation may also allow escalation of the mean dose, which is probably related to better efficacy. As a consequence of the present study, infusion rates should be standardised, and the potential of a dose reduction in the first cycle and of CYP3A4 phenotyping should be addressed in clinical studies.

Cyclophosphamide is an alkylating agent belonging to the group of oxazaphosporines. As cyclophosphamide is in clinical use for more than 40 years, there is a lot of experience using this drug for the treatment of cancer and as an immunosuppressive agent for the treatment of autoimmune and immune-mediated diseases. Besides antimitotic and antireplicative effects, cyclophosphamide has immunosuppressive as well as immunomodulatory properties. Cyclophosphamide shows selectivity for T cells and is therefore now frequently used in tumour vaccination protocols and to control post-transplant allo-reactivity in haplo-identical unmanipulated bone marrow after transplantation. The schedule of administration is of special importance for the immunological effect: while cyclophosphamide can be used in high-dose therapy for the complete eradication of haematopoietic cells, lower doses of cyclophosphamide are relatively selective for T cells. Of special interest is the fact that a single administration of low-dose cyclophosphamide is able to selectively suppress regulatory T cells (Tregs). This effect can be used to counteract immunosuppression in cancer. However, cyclophosphamide can also increase the number of myeloid-derived suppressor cells. Combination of cyclophosphamide with other immunomodulatory agents could be a promising approach to treat different forms of advanced cancer.

Background and Objective: Knowledge on the pharmacokinetics of doxorubicin, especially in children, is very limited with conflicting evidence concerning a possible age dependency in the pharmacokinetics. The aim of the current investigation was to assess, by using population pharmacokinetics, whether an age dependency in the clearance (CL) of doxorubicin exists. Methods: Pharmacokinetic data of doxorubicin and its main metabolite doxorubicinol from 94 children (aged 0–18 years) from the EPOC-MS-001-Doxo trial were available. A population pharmacokinetic model was developed in NONMEM® 7.2.0. Results: A linear three-compartment model for doxorubicin, with one additional compartment for doxorubicinol, gave the best fit to the data. All model parameters were linearly scaled on body surface area. Including a power function of age as a covariate for CL led to a further improvement of the model. Variation in genes encoding for enzymes involved in the metabolism or active transport of doxorubicin had no influence on the pharmacokinetics. Estimates of CL were lower (26.6 L/h/m2 in children aged >3 years and 21.1 L/h/m2 in children aged ≤3 years, p = 0.0004) in children aged

s / Biol Blood Marrow Transplant 21 (2015) S79eS107 S102 success using HLA-matched related donors; however, use of alternative donors has been associated with increased graft failure, graft versus host disease (GVHD), and transplantrelated mortality (TRM). HSCT using alternative donors with post-transplantation cyclophosphamide (PT/Cy) has been performed for hematologic malignancies with engraftment, GVHD, and TRM comparable to that seen with HLA-matched related donors. There are limited reports of HSCT in nonmalignant disorders using alternative donors and PT/Cy. Design: We transplanted 9 patients with non-malignant conditions (CGD1⁄43, DKC1⁄42, DBA1⁄41, HyperIgM1⁄41, XIAP1⁄41, IPEX1⁄41) using an alemtuzamab/fludarabine based reduced intensity conditioning (RIC). All patients received GVHD prophylaxis with PT/Cy, with the addition of mycophenolate mofetil and tacrolimus for HSCT with haploidentical donors and for alkylator-sensitive diagnoses (DKC). Six patients had 10/10 HLA-matched unrelated donors, and 3 had HLA-haploidentical related donors. Results: All 9 patients successfully engrafted by day 30. Ultimately, all patients have had sustained donor engraftment sufficient to eliminate manifestations of their underlying diseases. 6 of 9 patients are full donor chimeras off immunosuppression,1 patient is a stablemixed donor chimera (76% CD3+ T cells) off immunosuppression, 1 patient is a stable mixed donor chimera on a calcineurin inhibitor (CNI), and 1 patient had secondary graft failure but was ultimately retransplanted with myeloablative conditioning using the same donor, resulting in full donor chimerism and elimination of disease. One patient developed Grade 1 and one patient Grade 2 acute GVHD, both treated successfully with steroids and a CNI. Mild skin chronic GVHD developed in 1 patient, treated successfully with phototherapy. No serious infections occurred and there was no TRM. 1 patient developed veno-occlusive disease, treated successfully with defibrotide. Disease-free survival is 89% with a median follow-up of 14 months (6-30 months). The patient with secondary graft failure is now disease-free after myeloablative transplant, for an overall disease-free survival of 100% at a median of 14 months follow-up (6-60 months). Overall survival is 100%. Conclusion: We have observed successful engraftment sufficient to eliminate manifestations of disease, limited GVHD, and no TRM in 9 patients with nonmalignant disorders using alternative donors, RIC, and PT/Cy. RIC HSCT with PT/Cy shows promise for curing nonmalignant pediatric disorders, and potentially eliminates the need for CNI use after MUD BMT. Development of prospective clinical trials to confirm these observations is warranted.

We have introduced a dimethylacetamide-based i.v. formulation of busulfan into pediatrics with a dose intensity [as measured by area under curve (AUC)] comparable to that achieved by oral busulfan while reducing variability. The target AUC was defined at 1600+/-600 microM.min. The children received 15 doses of i.v. busulfan as 2-h infusions with a dose calculated to be 80% of the oral dose according to the malignancy-related protocol. The first infusion was applied as a double dose over 4 h with the second infusion following 12 h thereafter. Plasma samples were analyzed for busulfan by a validated LC-MS method and toxicity was assessed at least up to day 100+ after transplantation. Nineteen children (median age: 4 years, range: 0.9-17.3) were included. The AUC after the first dose ranged from 570 to 1410 microM.min [geometric mean 1010 microM.min, coefficient of variation (CV)=22%, n=17]. In nine out of 17 patients, the AUC after the first dose was out of the target range. Two patients had neurotoxic symptoms, which were attributable to busulfan in one individual. No case of severe hepatic veno-occlusive disease or other serious toxic events occurred. We conclude that i.v. busulfan displays a smaller interpatient variability in exposure compared to oral busulfan (CV of 24% after i.v. versus CV of 37% after oral busulfan). The equivalent dose to 1 mg/kg oral busulfan with regard to the AUC appears to be higher than 0.8 mg/kg.

The aim of this study was to describe the pharmacokinetics of paracetamol (acetaminophen) and to get primary information on its metabolism after first indicated intravenous administration of paracetamol in children and adolescents undergoing major surgery. About 4 weeks after the last chemotherapy, seven children and adolescents (five osteosarcoma, two Ewing tumors) received paracetamol infusion (median: 15.0 mg/kg) for analgesia. Sparse serum (37 samples; 4–7 per patient) and urine samples (27 samples; 0–15 per patient) were analyzed for paracetamol, paracetamol–glucuronide, paracetamol–sulfate, paracetamol–mercapturate and paracetamol–cysteine using capillary electrophoresis. Nonlinear mixed-effect models were used to describe the pharmacokinetics of paracetamol in plasma. Pharmacokinetics of paracetamol after intravenous administration was best described by a two-compartment model with clearance of 13.2 l/h per 70 kg (between-subject variability: 30%), intercompartmental clearance of 45.7 l/h per 70 kg (both parameters standardized to a 70-kg person using allometric “1/4 power models”), central volume of distribution of 13.2 l per 70 kg (between-subject variability: 71%) and peripheral volume of distribution of 33.0 l per 70 kg. Paracetamol, the glucuronide- and sulfate conjugates as well as cysteine and mercapturic acid conjugates, both products of oxidative pathways of paracetamol, were excreted in urine. Surgery, with all its potential influencing factors, together with chemotherapy given about 4 weeks previously do not seem to have a major impact on the pharmacokinetic behavior and the between-subject variability of paracetamol after intravenous administration.

Carboxypeptidase G2 (CPG2) is used when unexpected toxicity or renal failure occurs during high-dose methotrexate therapy. Leucovorin is also administered to antagonise the effects of methotrexate on purine anabolism. To investigate the effects of CPG2 on leucovorin rescue, we incubated the enzyme with both stereoisomers and analysed the degradation. A method for separating the stereoisomers of leucovorin, the internal standard aminopterin and the degradation products by capillary electrophoresis with 2.6-dimethyl-beta-cyclodextrin as a chiral selector has been developed. The active 6S-leucovorin is degraded much faster than the inactive 6R-isomer. The maximum observed degradation velocity was 31 microM/min for 6S-leucovorin and 20 microM/min for 6R-leucovorin, respectively, with an initial concentration of each stereoisomer of 250 microM. Similar results were obtained at lower concentrations of leucovorin isomers. Thus, the selectivity of CPG2 for methotrexate in comparison to leucovorin is not as high as anticipated in the literature as only the active 6S-leucovorin and not the mixture of the diastereomers should be taken into account. We conclude that the protective effects of leucovorin are antagonized by CPG2. Therefore, CPG2 should be administered to patients with caution.

Aims To investigate the population pharmacokinetics of daunorubicin in children after administration of liposomal daunorubicin (Daunoxome®). Methods Plasma samples from 19 children with relapsed acute myeloic leukaemia and five children with other malignancies were collected. Daunoxome® was administered as a 1- to 2.5 h infusion with doses ranging from 30 to 60 mg m−2. Overall, 214 samples were analysed for daunorubicin using capillary electrophoresis, and population pharmacokinetic modelling was performed using NONMEM. Results The data were best described by a one compartment model. Inclusion of interoccasion variability in the model (16.7% for clearance) improved strongly the precision of the estimates. The inclusion of body surface area or height as a covariate decreased interindividual variability. However, the best fit was obtained using the absolute dose, and when weight was included as a covariate for clearance (CL) and volume of distribution (V ). The final parameter estimates were: CL 6.41 ml h−1 kg−1± 0.5 51% and V 65.4 ml kg−1 ± 0.5 27% (population mean ± 0.5 interindividual variability). The area under the curve at a dose of 60 mg m−2 was 231 mg l −1h. Conclusions In comparison with free daunorubicin, Daunoxome® shows a low volume of distribution, a lower clearance and a lower interindividual variability in these parameters. This might be advantageous in reducing the variability in exposure to the drug.

Abdominal surgery may affect intestinal absorption and the resulting levels of posaconazole in the blood. We measured plasma posaconazole levels in surgical intensive care unit (SICU) patients and tried to develop a predictive population pharmacokinetics model. A total of 270 samples from 15 patients receiving posaconazole via nasogastric tube were measured by high-performance liquid chromatography (HPLC). SICU patients showed lower plasma drug concentrations, a higher apparent clearance, and a higher volume of distribution than those in hematology patients, possibly due to poor absorption.

Liposomal daunorubicin (DaunoXome) is a formulation of the anticancer drug daunorubicin encapsulated into vesicles of about 45 nm diameter. To understand the pharmacodynamic relationships associated with the toxicity and efficacy of liposome-encapsulated daunorubicin in vivo and in vitro, it is essential to have a rapid method of separating the free and liposomal forms of the drug. We have developed and validated a method to quantify drug concentrations of liposomal daunorubicin, free daunorubicin and its main metabolite daunorubicinol that requires only 50 microl of plasma to conduct studies in children. The method involves the use of solid-phase extraction followed by capillary electrophoresis with laser-induced fluorescence (LIF) detection. With LIF detection a limit of quantification of 1 microg/l is obtained for the free form and the metabolite. Precision and accuracy are in accordance with the generally accepted criteria for bioanalytical methods. The method is rapid and allows for multiple samples to be processed simultaneously.

This study investigates the impact of dose escalation and of doxorubicin and cyclophosphamide coadministration on the pharmacokinetics of etoposide (ETO). Pharmacokinetics of ETO were analyzed in seven patients with breast cancer receiving 3-4 cycles of conventional-dose (CD) and one final course of high-dose (HD) chemotherapy including ETO (450 mg/m(2) and 2100 mg/m(2), respectively, fractionated over 3 consecutive days). ETO was given as monoinfusion apart from day 1 of CD, where cyclophosphamide and doxorubicin were coadministered. Plasma samples obtained on day 1 and day 2 of CD- and HD-therapy, respectively, were analyzed for ETO by HPLC. Data from a total of 25 cycles of CD- and 7 cycles of HD-therapy are given as means +/- SD for CD-day 1, CD-day 2, HD-day 1 and HD-day 2, respectively. Following administration of 210+/-29, 278+/-41, 1143+/-79 and 1143+/-79 mg ETO, the AUC (0-24 h, normalized to 150 mg/m(2)) was 123+/-23, 113+/-22, 92+/-11 and 100+/-22 microgxh/ml. The AUC and CL of single-agent ETO were not significantly different between CD (day 2) and both days of HD ETO. However, we observed a modest but significant difference for AUC and CL between day 1 of CD (coadministration of doxorubicin and cyclophosphamide) and day 2 of CD (ETO monoinfusion), the AUC and CL being 9% higher (see above) and 10% lower (21.1 vs. 23.3 ml/minxm(2)) ( P

BACKGROUND: First-line treatment in AML commonly included high cumulative doses of anthracyclines with an increasing risk of cardiotoxicity. Liposomal daunorubicin (L-DNR) is thought to be less cardiotoxic without impairment of efficacy. METHODS: The AML-BFM REZ 97 study included two reinduction blocks with L-DNR (2 x 60 mg/m (2) n = 38, since 2/1999 3 x 60 mg/m (2) n = 31) combined with cytarabine (500 mg/m (2) 4 d). Children who achieved a second blast clearance were allocated to allogeneic stem cell transplantation either from a matched related (MRD) or a matched unrelated donor (MUD). Lack of a donor justified haploidentical SCT in early relapse (1st remission < 1 year) and autologous SCT in late relapse. PATIENTS: Between 1/1997 and 9/2001, 69 children were enrolled in the AML-BFM 97 relapse study. The median duration of first remission was 0.9 years. Forty-one patients had a remission of less than one year, 28 of more than a year. RESULTS: 46 children (67 %) achieved a second remission, defined as clearance of blasts in bone marrow and at least a partial hematological reconstitution. Seventeen of these children are alive (12 of 25 children receiving allogeneic SCT (MFD/MUD); 1 of 8 children after haploidentical SCT; 1 of 4 patients after autologous SCT and 3 of 9 patients treated with chemotherapy only). Further three children without 2nd remission survived after MFD-SCT (n = 2) or chemotherapy (n = 1; follow-up 0.3 to 0.7 years). Duration of first remission remains a significant prognostic factor. The pharmacokinetic investigation showed a high overall AUC of 234.6 mg/l h at a dose of 60 mg/m (2), and a volume of distribution of 1.98 l/m (2), which is much lower in comparison to conventional Daunorubicin. Regarding toxicity, the combination of L-DNR and cytarabine followed by SCT was feasible in experienced centers, however, acute complications like infection or septicemia in aplasia, mucositis and GvHD were common. By contrast, no clinical relevant cardiotoxicity was seen so far, but definitive results in long-term cardiotoxicity await a longer follow-up. In conclusion, L-DNR/cytarabine treatment induced a 2nd remission in most of the children with relapsed or refractory AML. It has to be followed by allogeneic SCT which enables long-term survival.

A physiologically based pharmacokinetic (PBPK) model of the DNA-alkylating agent busulfan was slightly modified and scaled from adults to children in order to predict the systemic busulfan drug exposure in children. Capitalizing on the recent major software release of PK-Sim®, we refined our PBPK model by implementing glutathione S transferase (GST) in 11 organs using the software integrated enzyme expression database. In addition, two irreversible binding processes (i.e., DNA and plasma protein binding) were applied by using Koff and KD values. The model was scaled from adults to children. Simulations were computed and compared to concentration-time data after intravenous (i.v.) busulfan administration to 36 children. Based on the results, an age-dependent enzyme activity and maturation ratio was tailored and evaluated with an external dataset consisting of 23 children. Initial adult to children scaling indicated lower clearance values for children in comparison to adults. Subsequent age-dependent maturation ratio resulted in three different age groups: Activity of busulfan-glutathione conjugate formation was 80%, 61%, and 89% in comparison to adults for children with an age of up to 2 years,2-6 years, and6-18 years, respectively. Patients of the evaluation dataset were simulated with a mean percentage error (MPE) for all patients of 3.9% with 3/23 children demonstrating a MPE of±30%. The PBPK model parameterization sufficiently described the observed concentration-time data of the validation dataset while showing an adequate predictive performance. This PBPK model could be helpful to determine the first dose of busulfan in children.

Purpose To overcome cytochrome P450 2D6 (CYP2D6) mediated tamoxifen resistance in postmenopausal early breast cancer, CYP2D6 phenotype-adjusted tamoxifen dosing in patients with impaired CYP2D6 metabolism and/or the application of endoxifen, the most potent tamoxifen metabolite, are alternative treatment options. To elucidate both strategies comprehensively we used a physiologically-based pharmacokinetic (PBPK) modeling approach. Methods Firstly simulation of increasing tamoxifen dosages was performed by a virtual clinical trial including populations of CYP2D6 poor (PM), intermediate (IM) and extensive metabolizers (EM) (N = 8,000). Secondly we performed PBPK-simulations under consideration of tamoxifen use plus concomitant increasing dosages of endoxifen (N = 7,000). Results Our virtual study demonstrates that dose escalation of tamoxifen in IMs resulted in endoxifen steady-state plasma concentrations similar to CYP2D6 EMs whereas PMs did not reach EM endoxifen levels. Steady-state plasma concentrations of tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen were similar in CYP2D6 IMs and PMs versus EMs using once daily dosing of 20 mg tamoxifen and concomitant CYP2D6 phenotype-adjusted endoxifen dosing in IMs and PMs (1 mg/d and 3 mg/d, respectively). Conclusion In conclusion, we suggest that co-administration of endoxifen in tamoxifen treated early breast cancer women with impaired CYP2D6 metabolism is a promising alternative to reach plasma concentrations comparable to CYP2D6 EM patients.

A new pegylated recombinant l-asparaginase (MC0609) was designed to improve pharmacokinetic characteristics and to further reduce immunogenicity in comparison with the currently marketed pegylated Escherichia coli l-asparaginase (pegaspargase, Oncaspar®). Comparative pharmacokinetics (PK), bioavailability, pharmacodynamics and immunogenicity studies were performed in CD® rats and Beagle dogs after intravenous (i.v.) and intramuscular (i.m.) single-dose administration of MC0609 or Oncaspar®. Bioanalytical data on enzymatic activity in serum of animals were used to develop a population pharmacokinetic (PopPK) model to simulate different dosages of MC0609 comparable to the activity time profile of Oncaspar®. In contrast to Oncaspar®, which showed an accelerated elimination over time, a constant serum elimination of enzymatic activity over time was seen for MC0609. Linear PK of MC0609 resulted in a prolonged and dose-dependent duration of enzymatic activity and longer depletion of l-asparagine in peripheral blood. The different PK characteristics of MC0609 and Oncaspar® were confirmed by PopPK analysis and model development. The PK parameters of Oncaspar® in dog scaled to body surface area were in the same range than the parameters determined in paediatric acute lymphoblastic leukaemia patients. Therefore, the dog is considered a clinically relevant model for PK evaluation of Oncaspar®. Distinct differences in immunogenic potential of both preparations were detected after single-dose administration of a therapeutic dose to dogs. An absolute bioavailability of 66 % was calculated for the intramuscular administration of MC0609. The new pegylated recombinant l-asparaginase preparation MC0609 revealed striking differences in PK/PD properties compared with Oncaspar® in rat and dog.

Purpose: The peak plasma concentrations seem to play an important role in the toxicity of the anthracyclines. As there are only limited data in the literature about the distribution of doxorubicin in children, we assessed the peak plasma concentrations of doxorubicin in pediatric patients. Patients and methods: We collected 87 plasma samples at the end of infusion from 27 children with acute lymphoblastic leukemia (ALL) or non-Hodgkin lymphoma (NHL) treated with 30 mg/m2 doxorubicin as a 1- or 2-h infusion once weekly for four weeks in the ALL-BFM 95 or NHL-BFM 95 protocol. Plasma concentrations of doxorubicin were quantified by capillary electrophoresis, and the peak plasma levels for a uniform 2-h infusion were calculated. Results: The geometric mean of all samples was 273 µg/l with a geometric coefficient of variation of 46.0%. This is in accordance with the peak plasma concentrations expected from simulations based on literature data from adults. High inter-individual as well as substantial intra-individual variability was observed. Girls had slightly higher peak plasma levels than boys. Age, weight, and body mass index as well as laboratory parameters had no influence on the peak plasma concentrations. No cumulation of doxorubicin during therapy was observed. Conclusion: The peak plasma concentrations are similar in adults and children for both the absolute values as well as the variability; this indicates that there are no major differences in the distribution of doxorubicin in children and adults.