Toward Model-Based Informed Precision Dosing of Vancomycin in Hematologic Cancer Patients: A First Step.

BACKGROUND AND OBJECTIVE: There is no consensus on the optimal vancomycin dose to achieve pharmacokinetic/pharmacodynamic (PK/PD) target in patients with hematologic cancer or in hematopoietic stem cell transplant (HSCT) recipients. A 24-h area under the concentration-time curve (AUC) >400 mg*h/L must be achieved early for successful treatment of severe methicillin-resistant Staphylococcus aureus (MRSA) infections. Current nomograms derived from general population data are not sufficiently accurate to allow AUC-based model-informed precision dosing. The objective of this study was to characterize vancomycin PK in patients with hematologic cancer or in HSCT recipients and to develop a model-informed dosing tool based on PK/PD target requirements. METHODS: Pooled retrospective and prospective vancomycin serum concentrations were analyzed using NONMEM® to evaluate the performance of previously published population PK (popPK) models built from hematologic cancer datasets and to develop a novel Bayesian PK model. Patients' characteristics and clinical data were tested as potential covariates. The popPK model was validated internally and externally. Predictions of vancomycin concentrations for different dosing regimens were made using Monte-Carlo simulations, and a nomogram strategy was proposed according to selected probability of target attainment (PTA). RESULTS: The predictive performance of the published popPK models was found to be suboptimal for our population. A novel popPK model was developed using 240 vancomycin concentrations (60 patients). A two-compartment structural model with an additive error model best described the data. Ideal body weight and estimated glomerular filtration rate (eGFR) [Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)] were selected as covariates for volume of distribution (V) and clearance (CL). Bootstrapping confirmed the stability and precision of the popPK parameters. The volume of distribution was V1 = 46.8 L and V2 = 56.1 L, while CL = 5.63 L/h. External validation using 107 vancomycin concentrations (24 patients) demonstrated the predictivity of the model. A nomogram was developed to reach minimally PTA >50% for 400 < AUC < 600 mg*h/L. CONCLUSION: To our knowledge, this study provides the first model-informed AUC-based strategy in North American hematologic cancer patients with or without HSCT. The resulting nomogram generated provides a simplified approach to improving the accuracy of initial vancomycin dosing in this population.

A randomized double-blind feasibility study comparing cetirizine and diphenhydramine in the prevention of paclitaxel-associated infusion-related reactions: the PREMED-F1 study.

PURPOSE: Cetirizine is a less sedative alternative to diphenhydramine for the prevention of infusion-related reactions (IRR) to paclitaxel. However, its use remains controversial. In this study, we assessed feasibility for a future definitive non-inferiority trial comparing cetirizine to diphenhydramine as premedication to prevent paclitaxel-related IRR. METHODS: This was a single-center randomized prospective feasibility study. Participants were paclitaxel-naive cancer patients scheduled to start paclitaxel chemotherapy. They were randomly assigned to receive either intravenous diphenhydramine 50 mg + oral placebo (control) or intravenous placebo + oral cetirizine 10 mg (intervention) for their first two paclitaxel treatments. The percentage of eligible patients completing a first paclitaxel treatment and the recruitment rate were assessed (feasibility outcomes). Drowsiness was measured at baseline and at selected time points using the Stanford Sleepiness Scale (SSS) (safety outcome). IRR events were also documented (efficacy outcome). RESULTS: Among 37 eligible patients, 27 were recruited and randomized (control 13; intervention 14) and 25 completed the study. The recruitment rate was 4.8 participants/month, meeting the primary feasibility target. Drowsiness was the main adverse effect associated with the premedication. The increase in drowsiness compared to baseline (ΔSSS) was greater in the diphenhydramine group compared to the cetirizine group (median ΔSSS 2 (IQR 3.25) vs median ΔSSS 0 (IQR 1), p < 0.01) when measured one hour after the premedication administration. One participant had an IRR and no unexpected serious adverse event occurred. CONCLUSION: The trial methods were feasible in terms of recruitment, retention, and safety. Cetirizine was significantly less sedating than diphenhydramine. IRR were infrequent and a larger trial is warranted to confirm non-inferiority for IRR prevention. TRIAL REGISTRATION: ClinicalTrials.gov, NCT04237090 (22.01.2020).

Pharmacokinetics of Tobramycin Administered at the Beginning of Intermittent Hemodialysis Session (ESRD Study).

BACKGROUND AND OBJECTIVES: There is a renewed interest in the successful use of aminoglycosides due to increasing resistance in gram-negative infections. Few studies to date have examined the pharmacokinetics (PK) of intradialytic infusions of tobramycin. This study sought to characterize the pharmacokinetic profile of intradialytically administered tobramycin in infected patients receiving chronic intermittent hemodialysis and to determine whether it is possible to achieve favorable PK targets. DESIGN SETTING PARTICIPANTS AND MEASUREMENTS: In this prospective pharmacokinetic study, a single dose (5 mg/kg) of tobramycin was administered intradialytically to 11 noncritically ill patients undergoing chronic intermittent hemodialysis. Blood samples were collected at selected time to determine tobramycin serum concentrations. The PK analysis was performed using Phoenix™ NLME. The efficacy exposure outcome for nonsevere gram-negative infections sensitive to tobramycin with a minimum inhibitory concentration ≤1 were maximum concentration (Cmax ≥ 10 mg/L) and area under the curve (AUC24 h > 30 mg⋅h/L). For toxicity, the goal was to identify plasma trough concentrations <2 mg/L. RESULTS: Tobramycin disposition was best described by a one-compartment model using a total clearance composed of the systemic clearance and a transitory hemodialysis clearance. Tobramycin mean (SD) Cmax, trough levels, and AUC24h were 13.1 (1.3) mg/L, 1.32 (0.47) mg/L, and 61 (23) mg⋅h/L, respectively. Monte Carlo simulation run with 1000 virtual patients showed that a 5 mg/kg dose of tobramycin administered intradialytically can outperformed the usual low-dose postdialysis dosing (80% meeting all targets versus <1%, respectively). CONCLUSIONS: A single high dose of tobramycin can achieve favorable PK outcome when administered using intradialytic infusions in hemodialysis patients. This practical dosing regimen may represent an effective and safer alternative to the usual dosing in the treatment of nonsevere gram-negative infections.

CONTEXTE ET OBJECTIFS: La résistance croissante des infections à Gram négatif suscite un regain d'intérêt pour l'utilisation efficace des aminoglycosides. À ce jour, peu d'études ont examiné la pharmacocinétique (PK) des infusions intradialytiques de tobramycine. La présente étude a tenté de caractériser le profil pharmacocinétique de la tobramycine administrée par infusion intradialytique chez des patients malades recevant des traitements intermittents d'hémodialyse de façon chronique. L'étude visait également à déterminer s'il est possible d'atteindre des objectifs de pharmacocinétique favorables. MÉTHODOLOGIE: Pour cette étude de pharmacocinétique prospective, une dose unique (5 mg/kg) de tobramycine a été administrée par infusion intradialytique à onze patients suivant des traitements d'hémodialyse intermittente de façon chronique ne nécessitant pas une admission aux soins intensifs. Des échantillons de sang ont été prélevés à des moments précis afin de mesurer les concentrations sériques de tobramycine. L'analyse de la PK a été effectuée à l'aide du PhoenixMC NLME. Les issues d'exposition d'efficacité avec une concentration minimale inhibitrice inférieure ou égale à 1 pour les infections à Gram négatifs non graves sensibles à la tobramycine étaient la concentration maximum (Cmax: ≥10 mg/L) et la surface sous la courbe (SSC24h: >30 mg⋅h/L). Quant à la toxicité, l'objectif était l'observation de concentrations plasmatiques inférieures à 2 mg/L. RÉSULTATS: La disponibilité de la tobramycine a été mieux décrite par un modèle à un compartiment utilisant une clairance totale composée de la clairance systémique et de la clairance transitoire de l'hémodialyse. La Cmax moyenne, la concentration minimale et la SSC24h de la tobramycine (écart-type) s'établissaient respectivement à 13,1 (1,3) mg/L, à 1,32 (0,47) mg/L et à 61 (23) mg⋅h/L. Une simulation de Monte Carlo réalisée avec 1 000 patients virtuels a montré qu'une dose unique de 5 mg/kg de tobramycine administrée par infusion intradialytique surpasse la faible dose normalement administrée après la dialyse (80 % des objectifs atteints pour la dose unique contre moins de 1 %, respectivement). CONCLUSIONS: Une dose unique élevée de tobramycine permet d'atteindre des paramètres pharmacocinétiques favorables si elle est administrée par infusion intradialytique chez les patients hémodialysés. Ce schéma posologique peut représenter une solution de remplacement efficace et plus sûre au dosage normalement administré pour le traitement des infections à Gram négatifs non graves.

Cytochrome p450 inhibitory properties of common efflux transporter inhibitors.

Drug transporter inhibitors are important tools to elucidate the contribution of transporters to drug disposition both in vitro and in vivo. These inhibitors are often unselective and affect several transporters as well as drug metabolizing enzymes, which can make experimental results difficult to interpret with confidence. We therefore tested 14 commonly used P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug-resistance associated protein (MRP) inhibitors as inhibitors of cytochrome P450 (P450) enzyme activities using recombinant enzymes. A subset of P-gp and/or CYP3A inhibitors were selected (cyclosporin A, elacridar, ketoconazole, quinidine, reserpine, and tacrolimus) for a comparison of P450 inhibition in human microsomes and hepatocytes. Most P-gp inhibitors showed CYP3A4 inhibition, with potencies often in a similar range as their P-gp inhibition, as well as less potent CYP2C19 inhibition. Other P450 enzymes were not strongly inhibited except a few cases of CYP2D6 inhibition. MRP and BCRP inhibitors showed limited P450 inhibition. Some inhibitors showed less P450 inhibition in human hepatocytes than human liver microsomes, for example, elacridar, probably due to differences in binding, permeability limitations, or active, P-gp mediated efflux of the inhibitor from the hepatocytes. Quinidine was a potent P450 inhibitor in hepatocytes but only showed weak inhibition in microsomes. Quinidine shows an extensive cellular uptake, which may potentiate intracellular P450 inhibition. Elacridar, described as a potent and selective P-gp inhibitor, displayed modest P450 inhibition in this study and is thus a useful model inhibitor to define the role of P-gp in drug disposition without interference with other processes.

Practical use of the regression offset approach for the prediction of in vivo intrinsic clearance from hepatocytes.

Systematic under-prediction of clearance is frequently associated with in vitro kinetic data when extrapolated using physiological scaling factors, appropriate binding parameters and the well-stirred model. The present study describes a method of removing this systematic bias through application of empirical correction factors derived from regression analyses applied to the in vitro and in vivo data for a defined set of reference compounds. Linear regression lines were established with in vivo intrinsic clearance (CLint), derived from in vivo clearance data and scaled in vitro intrinsic clearance from isolated hepatocyte incubations. The scaled CLint was empirically corrected to a predicted in vivo CLint using the slope and intercept from a uniform weighted linear regression applied to the in vitro to in vivo extrapolation. Cross validation of human data demonstrated that 66% of the reference compounds had a predicted in vivo CLint within two-fold of the observed value. The average absolute fold error (AAFE) for the in vivo CLint predictions was 1.90. For rat, 54% of the compounds had a predicted value within two-fold of the observed and the AAFE was 1.98. Three AstraZeneca projects are used to exemplify how a two-sided prediction interval, applied to the rat regression corrected reference data, can form the basis for assessing the likelihood that, for a given chemical series, the in vitro kinetic data is predictive of in vivo clearance and is therefore appropriate to guide optimisation of compound metabolic stability.

Discovery of P2X3 selective antagonists for the treatment of chronic pain.

Purinergic receptor P2X3 has been linked to analgesia in a number of pre-clinical models of pain, and is expressed in the human pain perception pathway. Only few P2X3-selective antagonists have been reported to date. This Letter describes the SAR and in vivo analgesic profile of a novel scaffold of selective P2X3 antagonists.

Selective downregulation of hepatic cytochrome P450 expression and activity in a rat model of inflammatory pain.

PURPOSE: This study was designed to examine the effect of Freund's complete adjuvant (FCA)-induced inflammation on liver P450 expression and activities in the first 7 days that followed a single FCA injection in the rat hindpaw. METHODS: Rats were humanely sacrificed at regular time points, plasma and liver samples were collected, liver mRNA extracted, and liver microsomes prepared. RESULTS: FCA injection led to the development of an acute inflammatory response evidenced by paw edema and increased alpha-1-acid glycoprotein (AGP) and total-nitrite (NOx) plasma concentrations. Plasma IL-6 levels were significantly higher in FCA-treated rats than in controls at 8 h post-FCA. Within 24 h, these changes were accompanied by a rapid decrease in total P450 contents in FCA-treated rat liver and the selective downregulation of specific CYP isoforms, as illustrated by decreased mRNA levels (CYP2B, CYP2CI1, CYP3A1, and CYP2E1), protein contents (CYP2B, CYP2C11, and CYP2E1) or catalytic activities (CYP2C6, CYP2C11, and CYP2E1). CYP3A1 mRNA levels were severely decreased by FCA administration, whereas CYP3A2 mRNA and protein levels remained unchanged. CONCLUSIONS: These early biochemical and metabolic modifications may have pharmacokinetic and pharmacodynamic consequences when hepatically cleared drugs are administered to FCA-treated rats, especially within the first 24-72 h post-FCA.

In vitro metabolism of chloroquine: identification of CYP2C8, CYP3A4, and CYP2D6 as the main isoforms catalyzing N-desethylchloroquine formation.

In humans, the antimalarial drug chloroquine (CQ) is metabolized into one major metabolite, N-desethylchloroquine (DCQ). Using human liver microsomes (HLM) and recombinant human cytochrome P450 (P450), we performed studies to identify the P450 isoform(s) involved in the N-desethylation of CQ. In HLM incubated with CQ, only DCQ could be detected. Apparent Km and Vmax values (mean +/- S.D.) for metabolite formation were 444 +/- 121 microM and 617 +/- 128 pmol/min/mg protein, respectively. In microsomes from a panel of 16 human livers phenotyped for 10 different P450 isoforms, DCQ formation was highly correlated with testosterone 6beta-hydroxylation (r = 0.80; p < 0.001), a CYP3A-mediated reaction, and CYP2C8-mediated paclitaxel alpha-hydroxylation (r = 0.82; p < 0.001). CQ N-desethylation was diminished when coincubated with quercetin (20-40% inhibition), ketoconazole, or troleandomycin (20-30% inhibition) and was strongly inhibited (80% inhibition) by a combination of ketoconazole and quercetin, which further corroborates the contribution of CYP2C8 and CYP3As. Of 10 cDNA-expressed human P450s examined, only CYP1A1, CYP2D6, CYP3A4, and CYP2C8 produced DCQ. CYP2C8 and CYP3A4 constituted low-affinity/high-capacity systems, whereas CYP2D6 was associated with higher affinity but a significantly lower capacity. This property may explain the ability of CQ to inhibit CYP2D6-mediated metabolism in vitro and in vivo. At therapeutically relevant concentrations ( approximately 100 microM CQ in the liver), CYP2C8, CYP3A4, and, to a much lesser extent, CYP2D6 are expected to account for most of the CQ N-desethylation.

Rapid and simple method to determine morphine and its metabolites in rat plasma by liquid chromatography-mass spectrometry.

A rapid and simple method for the determination of morphine (M), normorphine (NM), morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in plasma by high-performance liquid chromatographic separation with mass spectrometric detection (HPLC-MS) has been developed. Samples (40 microl) were cleaned-up by protein precipitation with two volumes (80 microl) of acetonitrile and reconstituted in formic acid 0.1% in water. Naloxone was used as internal standard. Analytes were separated on a phenyl-hexyl column using a step-gradient (1 ml/min) of acetonitrile and formic acid in water. Acetonitrile was added post-column (0.3 ml/min). Quantification of morphine and its metabolites was achieved with an Agilent 1100 series HPLC-MS system equipped with electrospray interface set to selected ion-monitoring (SIM) mode. Calibration curves covered a wide range of concentrations (2.44-10,000 nM) and were best fitted with a weighed quadratic equation. The limits of quantification achieved with this method were 2.44 nM for M and 4.88 nM for NM, M3G and M6G. The method proved accurate (85-98%), precise (C.V.<10%) and was successfully applied to a wide range of in vitro and in vivo pharmacokinetic studies in rodents.