Population pharmacokinetics of intravenous cefotaxime indicates that higher doses are required for critically ill children.

BACKGROUND: Cefotaxime is frequently used in critically ill children, however pharmacokinetic (PK) studies to support adequate dosing in this patient population are limited. OBJECTIVES: To characterize cefotaxime PK in critically ill children and evaluate exposures achieved by current and alternative dosing regimens. METHODS: Children (0-18 years) admitted to the paediatric ICU, receiving intravenous cefotaxime (100-150 mg/kg/day, interval 6-8 h) were included (Clinicaltrials.gov NCT03248349). Total plasma cefotaxime concentrations were measured on multiple study days. Population-PK analysis was performed using nonlinear mixed effects modelling (NONMEM™). Dose evaluations were performed using typical patients across the paediatric age range and target attainment was determined for MICs of 0.5, 2 and 4 mg/L. RESULTS: 479 cefotaxime plasma concentrations from 52 children (median age 1.6, range 0.03-17.7 years) were used to describe cefotaxime PK. We describe a two-compartment structural model with interindividual variability, including bodyweight as covariate for volume of distribution and clearance. Model predicted exposure for 150 mg/kg/day (current dose) showed trough concentrations <0.5 mg/L in patients >4 years of age. The maximum cefotaxime doses (200 mg/kg/day, interval 6 h) proved adequate for MICs ≤0.5 mg/L across the whole age range. Similar daily doses with increased frequency (interval 4 h) covered MICs up to 2 mg/L, while a loading dose followed by continuous infusion regimens are needed to adequately treat MICs of 4 mg/L. CONCLUSIONS: Higher cefotaxime doses are required for adequate exposure for most pathogens in critically ill children. A higher dose frequency or continuous infusion is advisable to improve target attainment for intermediately susceptible pathogens.

Midazolam Infusion and Disease Severity Affect the Level of Sedation in Children: A Parametric Time-to-Event Analysis.

AIM: In critically ill mechanically ventilated children, midazolam is used first line for sedation, however its exact sedative effects have been difficult to quantify. In this analysis, we use parametric time-to-event (PTTE) analysis to quantify the effects of midazolam in critically ill children. METHODS: In the PTTE analysis, data was analyzed from a published study in mechanically ventilated children in which blinded midazolam or placebo infusions were administered during a sedation interruption phase until, based on COMFORT-B and NISS scores, patients became undersedated and unblinded midazolam was restarted. Using NONMEM® v.7.4.3., restart of unblinded midazolam was analysed as event. Patients in the trial were divided into internal and external validation cohorts prior to analysis. RESULTS: Data contained 138 events from 79 individuals (37 blinded midazolam; 42 blinded placebo). In the PTTE model, the baseline hazard was best described by a constant function. Midazolam reduced the hazard for restart of unblinded midazolam due to undersedation by 51%. In the blinded midazolam group, time to midazolam restart was 26 h versus 58 h in patients with low versus high disease severity upon admission (PRISM II < 10 versus > 21), respectively. For blinded placebo, these times were 14 h and 33 h, respectively. The model performed well in an external validation with 42 individuals. CONCLUSION: The PTTE analysis effectively quantified the effect of midazolam in prolonging sedation and also the influence of disease severity on sedation in mechanically ventilated critically ill children, and provides a valuable tool to quantify the effect of sedatives. Clinical trial number and registry URL: Netherlands Trial Register, Trial NL1913 (NTR2030), date registered 28 September 2009 https://www.trialregister.nl/trial/1913 .

An HPLC-UV method for determining plasma dimethylacetamide concentrations in patients receiving intravenous busulfan.

Dimethylacetamide (DMA) is a solvent used in the preparation of intravenous busulfan, an alkylating agent used in blood or marrow transplantation. DMA may contribute to hepatic toxicity, so it is important to monitor its clearance. The aim of this study was to develop an HPLC-UV assay for measurement of DMA in human plasma. After precipitation of plasma proteins with acetonitrile followed by dilution (1:4) with water, the extract was injected onto the HPLC and detected at 195 nm. Separation was performed using a Cogent-HPS 5 µm C18 column (250 × 4.6 mm) preceded by a Brownlee 7 µm RP18 , pre-column (1.5 cm × 3.2 mm). The mobile phase was 25 mm sodium phosphate buffer (pH 3), containing 2.5% (v/v) acetonitrile and 0.0005% (v/v) sodium-octyl-sulfonate. Using a flow rate of 1 mL/min, the retention times of DMA and the internal standard (IS), 2-chloroacetamide, were 9.5 and 3.5 min, respectively. Peak area ratio (DMA:IS) was a linear function of concentration from 1 to 1000 µg/mL. There was excellent intraday precision (<5% for 5-700 µg/mL DMA), accuracy (<3% deviation from the true concentration) and recovery (74-98%). The limits of detection and quantification were 1 and 5 µg/mL, respectively. In eight children who received intravenous busulfan, DMA concentrations ranged from 110 to 438 µg/mL.

Identification of high-dimensional omics-derived predictors for tumor growth dynamics using machine learning and pharmacometric modeling.

Pharmacometric modeling can capture tumor growth inhibition (TGI) dynamics and variability. These approaches do not usually consider covariates in high-dimensional settings, whereas high-dimensional molecular profiling technologies ("omics") are being increasingly considered for prediction of anticancer drug treatment response. Machine learning (ML) approaches have been applied to identify high-dimensional omics predictors for treatment outcome. Here, we aimed to combine TGI modeling and ML approaches for two distinct aims: omics-based prediction of tumor growth profiles and identification of pathways associated with treatment response and resistance. We propose a two-step approach combining ML using least absolute shrinkage and selection operator (LASSO) regression with pharmacometric modeling. We demonstrate our workflow using a previously published dataset consisting of 4706 tumor growth profiles of patient-derived xenograft (PDX) models treated with a variety of mono- and combination regimens. Pharmacometric TGI models were fit to the tumor growth profiles. The obtained empirical Bayes estimates-derived TGI parameter values were regressed using the LASSO on high-dimensional genomic copy number variation data, which contained over 20,000 variables. The predictive model was able to decrease median prediction error by 4% as compared with a model without any genomic information. A total of 74 pathways were identified as related to treatment response or resistance development by LASSO, of which part was verified by literature. In conclusion, we demonstrate how the combined use of ML and pharmacometric modeling can be used to gain pharmacological understanding in genomic factors driving variation in treatment response.

Current Ceftriaxone Dose Recommendations are Adequate for Most Critically Ill Children: Results of a Population Pharmacokinetic Modeling and Simulation Study.

BACKGROUND AND OBJECTIVE: Ceftriaxone is a cornerstone antibiotic for critically ill children with severe infections. Despite its widespread use, information on the pharmacokinetics of ceftriaxone is lacking in this population. We aimed to determine ceftriaxone pharmacokinetics in critically ill children and to propose ceftriaxone dosing guidelines resulting in adequate target attainment using population pharmacokinetic modeling and simulation. METHODS: Critically ill children (aged 0-18 years) treated with intravenous ceftriaxone (100 mg/kg once daily, infused in 30 minutes) and a central or arterial line in place were eligible. Opportunistic blood sampling for total and unbound ceftriaxone concentrations was used. Population pharmacokinetic analysis was performed using non-linear mixed-effects modeling on NONMEM™ Version 7.4.3. Simulations were performed to select optimal doses using probability of target attainment for two pharmacokinetic targets of the minimum inhibitory concentration (MIC) reflecting the susceptibility of pathogens (f T > MIC 100% and fT > 4 × MIC 100%). RESULTS: Two hundred and five samples for total and 43 time-matched samples for unbound plasma ceftriaxone concentrations were collected from 45 patients, median age 2.5 (range 0.1-16.7) years. A two-compartment model with bodyweight as the co-variate for volume of distribution and clearance, and creatinine-based estimated glomerular filtration rate as an additional covariate for clearance, best described ceftriaxone pharmacokinetics. For a typical patient (2.5 years, 14 kg) with an estimated glomerular filtration rate of 80 mL/min/1.73 m2, the current 100-mg/kg once-daily dose results in a probability of target attainment of 96.8% and 60.8% for a MIC of 0.5 mg/L and 4 × MIC (2 mg/L), respectively, when using fT > MIC 100% as a target. For a 50-mg/kg twice-daily regimen, the probability of target attainment was 99.9% and 93.4%, respectively. CONCLUSIONS: The current dosing regimen of ceftriaxone provides adequate exposure for susceptible pathogens in most critically ill children. In patients with an estimated glomerular filtration rate of > 80 mL/min/1.73 m2 or in areas with a high prevalence of less-susceptible pathogens (MIC ≥ 0.5 mg/L), a twice-daily dosing regimen of 50 mg/kg can be considered to improve target attainment. CLINICAL TRIAL REGISTRATION: POPSICLE study (ClinicalTrials.gov, NCT03248349, registered 14 August, 2017), PERFORM study (ClinicalTrials.gov, NCT03502993, registered 19 April, 2018).

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the (Modern) Treatment of Melanoma.

Targeted therapies, based on identification of common oncogenic mutations such as BRAF V600E/K and monoclonal antibody immunotherapies, have transformed the treatment of melanoma. Dual mitogen-activated protein kinase (MAPK) pathway inhibition of BRAF V600E/K and MEK 1/2 kinases with BRAF-MEK inhibitors using dabrafenib-trametinib, vemurafenib-cobimetinib and encorafenib-binimetinib is now the standard of care for BRAF V600E/K tumours. Monoclonal antibodies, such as pembrolizumab and nivolumab, against programmed cell death protein (PD-1) on T cells, as well as ipilimumab against cytotoxic T lymphocyte antigen-4 (CTLA-4), enable restoration of suppressed T-cell antitumour response, and have also shown improved clinical benefit compared with traditional chemotherapy. Exploration of different combination therapies, sequence of treatment, and dosing strategies is ongoing, and the understanding of the pharmacokinetics (PK) and pharmacodynamics (PD) of these new agents is fundamental in devising the optimal regimen. Preclinical and clinical studies, as well as population PK modelling, provide essential data in terms of PK parameters, metabolism, interpatient variability, drug interactions and PD effects at the target. This review gathers the current evidence and understanding of the clinical PK and PD of drugs used in the modern treatment of melanoma, and the factors determining drug disposition, exposure and clinical response, and also highlighting areas of further research.