Romain Guilhaumou

Validation of an electrospray ionization LC/MS/MS method for quantitative analysis of vincristine in human plasma samples

Vincristine is a natural vinca alkaloid widely used in paediatric cancer treatment. Vincristine pharmacokinetics has been already studied, but few data are available in paediatric populations. A sensitive and specific liquid chromatography-tandem mass spectrometry (LC/MS/MS) method was developed for the quantification of vincristine in plasma in order to investigate pharmacokinetics in a paediatric population. Two hundred microliters of plasma was added to vinblastine, used as internal standard. Chromatographic separation was achieved on a C8 HPLC column (Phenomenex Luna 50 mm x 2.0 mm, 3.0 microm) with a mobile phase gradient at a flow rate of 0.2 ml/min. Quantification was performed using the transition of 825.4-->765.4 (m/z) for vincristine and 811.4-->751.4 (m/z) for vinblastine. Chromatographic separation was achieved in 8 min. The limit of quantification was 0.25 ng/ml with a precision of 10.2% and an accuracy of 99.6%. The calibration curve was linear up to 50.0 ng/ml. Intra-day precision and accuracy ranged from 6.3% to 10% and from 91.9% to 100.8%, respectively. Inter-assay precision and accuracy ranged from 3.8% to 9.7% and from 93.5% to 100.5%, respectively. No significant matrix effect was observed for vincristine. A rapid, specific and sensitive LC/MS/MS method for quantification of vincristine in human plasma was developed and is now successfully applied for pharmacokinetic studies in paediatric patients.

Population pharmacokinetics and pharmacogenetics of vincristine in paediatric patients treated for solid tumour diseases

PurposeThe interindividual variability of vincristine pharmacokinetics is quite large, but the origins of this variability are not properly understood. The aim of this study was to develop a population pharmacokinetic model of vincristine in a paediatric population treated for solid tumour disease and evaluate the impact of different ABCB1, CYP3A4 and CYP3A5 polymorphisms on the different pharmacokinetic parameters.MethodsWe assessed vincristine pharmacokinetics in 26 children treated for various solid tumour diseases. Genotypes were determined by real-time PCR with a LightCycler™ and ABCB1 haplotypes calculated using the software program Phase 2.1. Vincristine plasma concentrations were determined by LC–MS/MS, and a population approach was performed on 184 samples by the NONMEM computer program. Demographic, therapeutic and genotypic covariables were evaluated on vincristine pharmacokinetic parameters.ResultsThe frequency of CYP3A4*1A/*1A and *1A/*1B genotypes were 87.5 and 12.5%, respectively. CYP3A5*1/*3 and *3/*3 were observed in 20.8 and 79.2% of the patients, respectively. The three major haplotypes were (allelic frequencies) CGC (50%), CGT (14.6%) and TTT (23.2%). Vincristine pharmacokinetics was well described by a two-compartment model. Large interindividual and interoccasion variability were observed. The different polymorphisms studied did not improve the model prediction.ConclusionsCYP3A4, CYP3A5 and ABCB1 polymorphisms did not significantly affect in vivo vincristine pharmacokinetics. Our results demonstrate that vincristine pharmacokinetic variability cannot be explained by these genetic polymorphisms.

Effects of induced hyperthermia on pharmacokinetics of ropivacaine in rats.

Ropivacaine is a local anaesthetic used for epidural anaesthesia and postoperative pain relief. Hyperthermia is a very common sign of infection associated with variations in physiological parameters, which may influence drugs pharmacokinetics. The aim of this study was to determine the effects of induced hyperthermia on ropivacaine pharmacokinetics in rats. Two groups of six rats were given a single subcutaneous ropivacaine injection. Hyperthermia‐induced animals were placed in a water bath to obtain a stable mean core temperature of 39.7 °C. After blood samples collection, ropivacaine serum concentrations and pharmacokinetic parameters were determined. Two other groups of six rats were sacrificed 30 min after ropivacaine injection to determine serum and tissues (brain and heart) concentrations. Our results (median ± inter quartile range) reveal a significant increase of the total apparent clearance (0.0151 ± 0.000800 L/min vs. 0.0134 ± 0.00134 L/min), apparent volume of distribution (Vd) (2.19 ± 0.27 L vs. 1.57 ± 0.73 L) and a significant decrease in exposure (488 ± 50.6 mg.min/L vs. 572 ± 110 mg.min/L) in induced‐hyperthermia group. We observed a significant increase in brain ropivacaine concentration in hyperthermic rats (8.39 ± 8.42 μg/g vs. 3.48 ± 3.26 μg/g) and no significant difference between cardiac concentrations in the two groups (5.38 ± 4.83 μg/g vs. 3.73 ± 2.44 μg/g). Results suggest a higher tissular distribution of ropivacaine and an increase in blood–brain barrier permeability during hyperthermia. The hyperthermia‐induced increase in Vd could be responsible for an increase in cerebral ropivacaine toxicity. These experimental data provide a basis for future clinical investigations in relation to local anaesthetic use in hyperthermic patients.

Pediatric Patients With Solid or Hematological Tumor Disease: Vancomycin Population Pharmacokinetics and Dosage Optimization.

Background: In pediatric cancer patients, determination of optimal vancomycin dosage is essential because of high risk of inadequate concentrations and bacterial resistance. The aim of this study was to determine vancomycin pharmacokinetic parameters in this population and propose dosage optimization to achieve optimal concentration. Methods: We retrospectively reviewed the use of vancomycin in pediatric cancer patients with febrile neutropenia (hematological or solid tumor disease). Vancomycin was administered by continuous infusion, and dosages were adapted according to therapeutic drug monitoring results. Blood cultures were performed before the first dose of antibiotic. Vancomycin pharmacokinetic population parameters were determined using NONMEM software, and dosage simulations were performed according to the target concentration (20–25 mg/L). Results: One hundred twenty-one patients were included in this study, representing 301 vancomycin concentrations. Blood cultures were positive in 37.5% of patients, and observed pathogens were mainly Staphylococcus spp. (43.8% methicillin resistant). Volume of distribution (95% confidence interval) was 34.7 L (17.3–48.0), and total apparent clearance (CL) (95% confidence interval) was correlated to body weight, tumor disease, and cyclosporine coadministration: CL = &thgr;CL × (WT/70)0.75 L/h with &thgr;CL = 3.49 (3.02–3.96), 4.66 (3.98–5.31), and 4.97 (4.42–5.41) in patients managed for hematological malignancies with or without cyclosporine coadministration and for solid malignancies, respectively. Based on simulation results, vancomycin dosage (milligram per kilogram) should be adapted to each child on the basis of its body weight and cyclosporine coadministration. Conclusions: Our results highlight the requirement to adapt vancomycin dosage in cancer pediatric population. Simulations have allowed to describe new dosage schedules, and a chart was created for clinicians to adapt vancomycin dosage.

Phenobarbital in intensive care unit pediatric population: predictive performances of population pharmacokinetic model

An external evaluation of phenobarbital population pharmacokinetic model described by Marsot et al. was performed in pediatric intensive care unit. Model evaluation is an important issue for dose adjustment. This external evaluation should allow confirming the proposed dosage adaptation and extending these recommendations to the entire intensive care pediatric population. External evaluation of phenobarbital published population pharmacokinetic model of Marsot et al. was realized in a new retrospective dataset of 35 patients hospitalized in a pediatric intensive care unit. The published population pharmacokinetic model was implemented in nonmem 7.3. Predictive performance was assessed by quantifying bias and inaccuracy of model prediction. Normalized prediction distribution errors (NPDE) and visual predictive check (VPC) were also evaluated. A total of 35 infants were studied with a mean age of 33.5 weeks (range: 12 days–16 years) and a mean weight of 12.6 kg (range: 2.7–70.0 kg). The model predicted the observed phenobarbital concentrations with a reasonable bias and inaccuracy. The median prediction error was 3.03% (95% CI: −8.52 to 58.12%), and the median absolute prediction error was 26.20% (95% CI: 13.07–75.59%). No trends in NPDE and VPC were observed. The model previously proposed by Marsot et al. in neonates hospitalized in intensive care unit was externally validated for IV infusion administration. The model‐based dosing regimen was extended in all pediatric intensive care unit to optimize treatment. Due to inter‐ and intravariability in pharmacokinetic model, this dosing regimen should be combined with therapeutic drug monitoring.

Effects of hyperthermia on pharmacokinetics of ertapenem in rats

The aim of this study was to document the influence of hyperthermia on the pharmacokinetics of ertapenem. Two groups of Wistar rats, normothermic (n = 6) and hyperthermic (n = 8), were injected a single intravenous bolus of ertapenem (15 mg/kg of body weight). Hyperthermia‐induced animals were placed in a water‐bath at 47 °C and control group animals were kept in a water‐bath at 25 °C to obtain a stable mean core temperature of 39.8 and 36.9 °C respectively. Hyperthermia induced significant higher plasma concentrations and exposure, whereas total apparent clearance and volume of distribution were significantly decreased. If confirmed in humans, these results will be of interest to take into account such modifications in hyperthermic clinical situations.

Analytical interference during cefepime therapeutic drug monitoring in intensive care patient: About a case report

β-lactams therapeutic drug monitoring (TDM) appears as an essential tool to ensure the achievement of pharmacokinetic-pharmacodynamic targets and prevent induced toxicity in intensive care unit patients. Indeed, those patients exhibit important pharmacokinetic variabilities that could lead to unpredictable plasma concentrations, potentially associated with poor clinical outcome, development of antibiotic resistance or increased side effects. Here, we report the case of a 48-year-old-patient admitted to intensive care unit and treated by cefepime using TDM. Due to inconsistency between observed cefepime plasma concentrations and patient clinical examination, investigations were started. After analytical tests, we highlighted an underlying analytical interference that overestimated cefepime plasma concentration with our in-house high performance liquid chromatography with ultraviolet detection (HPLC-UV) method. Only the inadequacy between plasmatic concentration and patient situation alerted pharmacologists and clinicians. As we found no previous case in literature, we believe this report must serve as an example of analytical limits that required pharmacologist awareness and expertise in TDM realization.

Concentrations systémiques d’antibiotiques potentiellement toxiques après administration par pansement imprégné chez un patient brûlé : à propos d’un cas clinique☆

Severe burned patients present high risk of skins infections, frequently due to Pseudomonas aeruginosa. Impregnated dressings with amikacin or colistin could be a good alternative to obtain effective concentration directly at the infected site. Therapeutic drug monitoring for these antibiotics is currently recommended after an intravenous administration to obtain effective and non-toxic plasmatic concentrations. However, data are lacking about systemic exposition and risk of toxicity after an administration with impregnated dressings. We report the case of a severe burned patient with cutaneous infection treated with amikacin and colistin impregnated dressings, for which plasmatic pharmacokinetic profiles were performed.