A rapid LC-MS/MS method for the simultaneous quantification of ivacaftor, lumacaftor, elexacaftor, tezacaftor, hexyl-methyl ivacaftor and ivacaftor carboxylate in human plasma.

Cystic fibrosis is one of the most common genetic diseases among caucasian population. This disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding for the CFTR protein. Lumacaftor, elexacaftor, tezacaftor, and ivacaftor were currently used as the treatment to Cystic fibrosis. In this study, we describe a new method for the simultaneous quantification of four molecules: lumacaftor, elexacaftor, tezacaftor, and ivacaftor, alongside two metabolites of ivacaftor, specifically hexyl-methyl ivacaftor and ivacaftor carboxylate by liquid chromatography-tandem mass spectrometry. This method holds significant utility for therapeutic drug monitoring and the optimization of treatments related to CFTR modulators. Molecules were extracted from 100 µL of plasma by a simple method of protein precipitation using acetonitrile. Following extraction, chromatographic separation was carried out by reverse chromatography on a C18 analytical column, using a gradient elution of water (0.05 % formic acid, V/V) and acetonitrile (0.05 % formic acid, V/V). The run time was 7 minutes at a flow rate of 0.5 mL/min. After separation, molecules were detected by electrospray ionization on a Xevo TQD triple-quadrupole-mass-spectrometer (Waters®, Milford, USA). The calibration range were: 0.053-20.000 mg/L for elexacaftor, tezacaftor and lumacaftor, 0.075-14.000 mg/L for ivacaftor, and 0.024-6.500 mg/L for hexyl-methyl ivacaftor and ivacaftor carboxylate. The proposed method underwent throughout validation demonstrating satisfactory precision (inter- and intra-day coefficients of variation less than 14.3 %) and a good accuracy (inter- and intra-day bias ranging between -13.7 % and 14.7 %) for all the analytes. The presented method for the simultaneous quantification of CFTR modulators and their metabolites in human plasma has undergone rigorous validation process yielding good results including strong precision and accuracy for all analytes. This method has been effectively used in routine analytical analysis and clinical investigations within our laboratory.

Optimization of vigabatrin dosage in children with epileptic spasms: A population pharmacokinetic approach.

AIMS: Vigabatrin is an antiepileptic drug used to treat some forms of severe epilepsy in children. The main adverse effect is ocular toxicity, which is related to the cumulative dose. The aim of the study is to identify an acceptable exposure range, both through the development of a population pharmacokinetic model of vigabatrin in children enabling us to calculate patient exposure and through the study of therapeutic response. METHODS: We performed a retrospective study including children with epilepsy followed at Necker-Enfants Malades hospital who had a vigabatrin assay between January 2019 and January 2022. The population pharmacokinetic study was performed on Monolix2021 using a nonlinear mixed-effects modelling approach. Children treated for epileptic spasms were classified into responder and nonresponder groups according to whether the spasms resolved, in order to identify an effective plasma exposure range. RESULTS: We included 79 patients and analysed 159 samples. The median age was 4.2 years (range 0.3-18). A 2-compartment model with allometry and creatinine clearance on clearance best fit our data. Exposure analysis was performed on 61 patients with epileptic spasms. Of the 22 patients who responded (36%), 95% had an AUC0-24 between 264 and 549 mg.h.L-1. CONCLUSIONS: The population pharmacokinetic model allowed us to identify bodyweight and creatinine clearance as the 2 main factors explaining the observed interindividual variability of vigabatrin. An acceptable exposure range was defined in this study. A target concentration intervention approach using this pharmacokinetic model could be used to avoid overexposure in responder patients.

Lumacaftor/Ivacaftor Population Pharmacokinetics in Pediatric Patients with Cystic Fibrosis: A First Step Toward Personalized Therapy.

BACKGROUND: A major breakthrough in cystic fibrosis (CF) therapy was achievedAQ1 with CFTR modulators. The lumacaftor/ivacaftor combination is indicated for the treatment of CF in pediatric patients above 6 years old. Pharmacokinetic (PK) studies of lumacaftor/ivacaftor in these vulnerable pediatric populations are AQ2crucial to optimize treatment protocols. OBJECTIVES AND METHODS: The objectives of this study were to describe the population PK (PPK) of lumacaftor and ivacaftor in children with CF, and to identify factors associated with interindividual variability. The association between drug exposure and clinical response was also investigated. RESULTS: A total of 75 children were included in this PPK study, with 191 concentrations available for each compound and known metabolites (lumacaftor, ivacaftor, ivacaftor-M1, and ivacaftor-M6). PPK analysis was performed using Monolix software. A large interindividual variability was observed. The main sources of interpatient variability identified were patient bodyweight and hepatic function (aspartate aminotransferase). Forced expiratory volume in the first second (FEV1) was statistically associated with the level of exposure to ivacaftor after 48 weeks of treatment. CONCLUSIONS: This study is the first analysis of lumacaftor/ivacaftor PPK in children with CF. These data suggest that dose adjustment is required after identifying variability factors to optimize efficacy. The use of therapeutic drug monitoring as a basis for dose adjustment in children with CF may be useful.

Pharmacokinetic of ceftazidime-avibactam in a critically ill patient under high-volume continuous venovenous haemodiafiltration: A first paediatric case report.

Ceftazidime-avibactam is a novel cephalosporin/B-lactamase inhibitor developed in the context of increasing resistance. This case reports the pharmacokinetics of ceftazidime-avibactam in a critically ill child under continuous renal replacement (CRRT) therapy for fluid overload. The patient was a 6-month-old female with sepsis due to bloodstream infection to Stenotrophomonas maltophilia following stem cell transplantation for severe combined immunodeficiency. CRRT was started on Day 2. Concentrations have been monitored using liquid chromatography-tandem mass spectrometry. Treatment was given every 8 h with a 2 h infusion of 30-7,5 mg/kg and did not reach pharmacokinetic/pharmacodynamic targets. Total clearance was respectively 1.7 and 3.02 L/h, with CRRT clearance respectively 28.8%-60% for ceftazidime and 14%-33% for avibactam. Those clearances are higher than reported in adult literature leading to a risk of treatment failure and emerging resistance. This supports the benefit of monitoring antimicrobial therapy under CRRT and the necessity to assess higher dosing or continuous infusion of ceftazidime-avibactam.

Piperacillin Population Pharmacokinetics and Dosing Regimen Optimization in Critically Ill Children Receiving Continuous Renal Replacement Therapy.

We aimed to develop a piperacillin population pharmacokinetic (PK) model in critically ill children receiving continuous renal replacement therapy (CRRT) and to optimize dosing regimens. The piperacillin plasma concentration was quantified by high-performance liquid chromatography. Piperacillin PK was investigated using a nonlinear mixed-effect modeling approach. Monte Carlo simulations were performed to compute the optimal scheme of administration according to the target of 100% interdose interval time in which concentration is one to four times above the MIC (100% fT > 1 to 4× MIC). A total of 32 children with a median (interquartile range [IQR]) postnatal age of 2 years (0 to 11), body weight (BW) of 15 kg (6 to 38), and receiving CRRT were included. Concentration-time courses were best described by a one-compartment model with first-order elimination. BW and residual diuresis (Qu) explained some between-subject variabilities on volume of distribution (V), where [Formula: see text], and clearance (CL), where [Formula: see text], where CLpop and Vpop are 6.78 L/h and 55.0 L, respectively, normalized to a 70-kg subject and median residual diuresis of 0.06 mL/kg/h. Simulations with intermittent and continuous administrations for 4 typical patients with different rates of residual diuresis (0, 0.1, 0.25, and 0.5 mL/kg/h) showed that continuous infusions were appropriate to attain the PK target for patients with residual diuresis higher than 0.1 mL/kg/h according to BW and MIC, while for anuric patients, less frequent intermittent doses were mandatory to avoid accumulation. Optimal exposure to piperacillin in critically ill children on CRRT should be achieved by using continuous infusions with escalating doses for high-MIC bacteria, except for anuric patients who require less frequent intermittent doses.

Meropenem Population Pharmacokinetics and Dosing Regimen Optimization in Critically Ill Children Receiving Continuous Renal Replacement Therapy.

BACKGROUND AND OBJECTIVE: We aimed to develop a meropenem population pharmacokinetic model in critically ill children receiving continuous renal replacement therapy and simulate dosing regimens to optimize patient exposure. METHODS: Meropenem plasma concentration was quantified by high-performance liquid chromatography. Meropenem pharmacokinetics was investigated using a non-linear mixed-effect modeling approach. Monte Carlo simulations were performed to compute the optimal scheme of administration, according to the target of a 100% inter-dose interval time in which concentration is one to four times above the minimum inhibitory concentration (100% fT>1-4×MIC). RESULTS: A total of 27 patients with a median age of 4 [interquartile range 0-11] years, a median body weight of 16 [range 7-35] kg receiving continuous renal replacement therapy were included. Concentration-time courses were best described by a one-compartment model with first-order elimination. Body weight (BW) produced significant effects on volume of distribution (V) and BW and continuous renal replacement therapy effluent flow rate (Qeff) produced significant effects on clearance (CL): [Formula: see text] and [Formula: see text], where Vpop and CLpop estimates were 32.5 L and 5.88 L/h, respectively, normalized to a 70-kg BW and median Qeff at 1200 mL/h. Using this final model and Monte Carlo simulations, for patients with Qeff over 1200 mL/h, meropenem continuous infusion was adequate in most cases to attain 100% fT>1-4xMIC. For bacterial infections with a low minimum inhibitory concentration (≤2 mg/L), meropenem intermitent administration was appropriate for patients weighing more than 20 kg with Qeff <500 mL/h and for patients weighing more than 10 kg with Qeff <100 mL/h. CONCLUSIONS: Meropenem exposure in critically ill children receiving continuous renal replacement therapy needs dosing adjustments to the minimum inhibitory concentration that take into account body weight and the continuous renal replacement therapy effluent flow rate.

Cefepime population pharmacokinetics and dosing regimen optimization in critically ill children with different renal function.

OBJECTIVE: Cefepime is commonly used in pediatric intensive care units, where unpredictable variations in the patients' pharmacokinetic (PK) variables may require drug dose adjustments. The objectives of the present study were to build a population PK model for cefepime in critically ill children and to optimize individual initial dosing regimens. METHODS: Children (aged from 1 month to 18 years; body weight >3 kg) receiving cefepime were included. Cefepime total plasma concentrations were measured using high performance liquid chromatography. Data were modelled using nonlinear, mixed-effect modeling software, and Monte Carlo simulations were performed with a PK target of 100% fT > MIC. RESULTS: Fifty-nine patients (median (range) age: 13.5 months (1.1 months to 17.6 years)) and 129 cefepime concentration measurements were included. The cefepime concentration data were best fitted by a one-compartment model. The selected covariates were body weight with allometric scaling and estimated glomerular filtration rate on clearance. Mean population values for clearance and volume were 1.21 L/h and 4.8 L, respectively. According to the simulations, a regimen of 100 mg/kg/d q12 h over 30 min or 100 mg/kg/d as a continuous infusion was more likely to achieve the PK target in patients with renal failure and in patients with normal or augmented renal clearance, respectively. DISCUSSION: Appropriate cefepime dosing regimens should take renal function into account. Continuous infusions are required in critically ill children with normal or augmented renal clearance, while intermittent infusions are adequate for children with acute renal failure. Close therapeutic drug monitoring is mandatory, given cefepime's narrow therapeutic window.

Therapeutic Drug Monitoring of Antibiotics in Critically Ill Children: An Observational Study in a Pediatric Intensive Care Unit.

BACKGROUND: Septic critically ill children are at a high risk of inadequate antibiotic exposure, requiring them to undergo therapeutic drug monitoring (TDM). The aim of this study was to describe the use of TDM for antibiotics in critically ill children. METHODS: The authors conducted a single-center observational study between June and December 2019, with all children treated with antibiotics in a pediatric intensive care unit located in a French university hospital. Standard clinical and laboratory data were recorded. Blood samples were collected for routine laboratory tests, and plasma antibiotic levels were assayed using validated analytical methods. RESULTS: A total of 209 children received antibiotics. TDM was performed in 58 patients (27.8%) who had a greater mean organ dysfunction (according to the International Pediatric Sepsis Consensus Conference) (3 versus 1 in the non-TDM group; P < 0.05) and were treated with antibiotics for longer. A total of 208 samples were analyzed. The median [interquartile range] assay turnaround time was 3 (1-5) days, and 48 (46.2%) of the 104 initial antibiotic concentration values were below the pharmacokinetic/pharmacodynamic targets. A total of 34 (46%) of the 74 off-target TDM measurements available before the end of the antibiotic treatment prompted dose adjustment. This dose adjustment increased the proportion of on-target TDM measurements (70% versus 20% without adjustment). Subsequent measurements of the minimum inhibitory concentration showed that the use of the European Committee on Antimicrobial Susceptibility Testing's epidemiological cutoff values led to underestimation of pharmacokinetic/pharmacodynamic target attainment in 10 cases (20%). CONCLUSIONS: TDM seems to be an effective means of optimizing antibiotic exposure in critically ill children. This requires timely plasma antibiotic assays and minimum inhibitory concentration measurements. It is important to define which patients should undergo TDM and how this monitoring should be managed.

Oral levofloxacin: population pharmacokinetics model and pharmacodynamics study in bone and joint infections.

OBJECTIVES: This study aimed at characterizing the pharmacokinetics (PK) of oral levofloxacin in adult patients in order to optimize dosing scheme and explore the PK/pharmacodynamics (PD) of levofloxacin in bone and joint infections (BJIs). METHODS: From November 2015 to December 2019, all patients hospitalized in Cochin Hospital, treated with levofloxacin and who had at least one dosage for therapeutic drug monitoring were included. PK was described using non-linear mixed-effect modelling. In a subgroup of patients with BJIs, the association between PK, MIC for the isolated pathogen and clinical outcome was investigated. Monte Carlo simulations investigated dosing regimens to achieve the PK/PD target (AUC/MIC ratio >100). RESULTS: One hundred and two patients were included (199 measurements), including 32 treated for BJI. A one-compartment model with first-order absorption and elimination best described the data. Effects of estimated creatinine clearance (eCLCR) and age were significant on levofloxacin clearance. In BJI patients, no significant association was found between levofloxacin PK/microbiological parameters and either clinical outcome or adverse events. Based on our model, we proposed optimized oral levofloxacin dosing regimens according to renal function, to reach the PK/PD target AUC/MIC ratio >100 for three frequent causative pathogens (Staphylococcus aureus, Enterobacterales and Pseudomonas aeruginosa). CONCLUSIONS: Our results reinforce the need of determining the MIC and using therapeutic drug monitoring in complex infections caused by P. aeruginosa.

Predictive Performance of Population Pharmacokinetic Models of Levetiracetam in Children and Evaluation of Dosing Regimen.

Levetiracetam is a broad-spectrum antiepileptic drug that exhibits high interindividual variability in serum concentrations in children. A population pharmacokinetic approach can be used to explain this variability and optimize dosing schemes. The objectives are to identify the best predictive population pharmacokinetic model for children and to evaluate recommended doses using simulations and Bayesian forecasting. A validation cohort included children treated with levetiracetam who had a serum drug concentration assayed during therapeutic drug monitoring. We assessed the predictive performance of all the population pharmacokinetic models published in the literature using mean prediction errors, root mean squared errors, and visual predictive checks. A population model was finally constructed on the data, and dose simulations were performed to evaluate doses. We included 267 levetiracetam concentrations ranging from 2 to 69 mg/L from 194 children in the validation cohort. Six published models were externally evaluated. Most of the models underestimated the variability of our population. A 1-compartment model with first-order absorption and elimination with allometric scaling was finally fitted on our data. In our cohort, 57% of patients had a trough concentration <12 mg/L and 12% <5 mg/L. To reach a trough concentration >5 mg/L, doses ≥30 mg/kg/d for patients ≤50 kg and ≥2000 mg/d for patients >50 kg are required. In our population, a high percentage of children had low trough concentrations. Our population pharmacokinetic model could be used for therapeutic drug monitoring of levetiracetam in children.

Development of a simple and rapid method to determine the unbound fraction of dolutegravir, raltegravir and darunavir in human plasma using ultrafiltration and LC-MS/MS.

Dolutegravir, raltegravir and darunavir are three antiretroviral drugs widely used in combined antiretroviral therapies. These three drugs are highly bound to plasma proteins. Compared to the total concentration, the concentration of unbound drug which is considered as the only pharmacological active form should be more informative to improve therapeutic drug monitoring in patients to avoid virological failure or toxicity. The aim of the present study was to develop an ultrafiltration protocol and a LC-MS/MS method to simultaneously determine the concentrations of the unbound dolutegravir, raltegravir and darunavir in human plasma. Finally, 150 µL of plasma was ultrafiltrated using Centrifree® ultrafiltration devices with ultracel YM-T membrane (cutoff 30 KDa) during 5 min at 37 °C at 1500 g. Then, 20 µL of the ultrafiltrate were injected into the LC-MS/MS system. The chromatographic separation was carried out on a BEH C18 column using a mobile phase containing deionized water and acetonitrile, both with 0.05 % (v/v) of formic acid, with a gradient elution at a flow rate of 0.5 mL/min. The run time was only 4 min. The calibration curve ranged from 0.5-200 ng/mL for dolutegravir, 1 to 400 ng/mL for raltegravir and 10-4000 ng/mL for darunavir. This method was validated with a good precision (inter- and intra-day CV% lower than 14 %) and a good accuracy (inter- and intra-day bias between -5.6-8.8 %) for all the analytes. This method is simple, reliable and suitable for pharmacokinetic studies.

Estimation of piperacillin clearance with different glomerular filtration rate formulas in critically ill children.

AIMS: Glomerular filtration rate (GFR) is difficult to assess in critically ill children using gold standard method and alternatives are needed. This study aimed to determine the most accurate GFR estimation formula for assessing piperacillin clearance in critically ill children, using a published piperacillin pharmacokinetics (PK) population model. METHODS: All children hospitalized in the paediatric intensive care unit of a single institution who were receiving piperacillin were included. PK were described using the nonlinear mixed effect modelling software MONOLIX. In the initial PK model, GFR was estimated according to the Schwartz 1976 formula. We evaluated a set of 12 additional validated formulas, developed using plasma creatinine and/or cystatin C concentrations, in the building model to assess the lowest between-subject variability for piperacillin clearance. RESULTS: We included 20 children with a median (range) postnatal age of 1.9 (0.1-19) years, body weight of 12.5 (3.5-69) kg. Estimated GFR according to the Schwartz 1976 formula was 160.5 (38-315) mL min-1 1.73 m-2 . Piperacillin clearance was best predicted by the Bouvet combined formula. CONCLUSION: The combined Bouvet formula was the most accurate GFR estimation formula for assessing piperacillin clearance in critically ill children.