Comparison between the immunoassay and high performance liquid chromatography for therapeutic monitoring of carbamazepine and phenytoine

Objective: To investigate the correlation of the immunoassay and chromatography method for quantitative measurement of two antiepileptic drugs (AED), carbamazepine (CBZ) and phenytoin (PHT) and determination of relation between the CBZ and it\u27s metabolite carbamazepine 10,11-epoxide (CBZ-E). Additionally we investigated whether there is a difference in the determination of serum concentration of CBZ and PHT when measured in two different labs by high performance liquid chromatography (HPLC). Materials and methods: This study was carried out on 102 blood samples (72 CBZ and 30 PHT) collected from epileptic outpatients. Plasma concentrations of CBZ and PHT were determined by validated HPLC (Shimadzu and Agilent) and the CEDIA-immunoassay method. Results: The correlations of serum concentrations of CBZ between CEDIA and HPLC1 and between CEDIA and HPLC2 were good (R = 0.97 for both techniques). Even better correlation was found between concentrations of CBZ measured by the two HPLC systems (R = 0.99). Similar, for PHT, we found good correlation between CEDIA and the two systems of HPLC (HPLC1 and HPLC2, R = 0.98) and between the two systems of HPLC of R =0.98. The moderate correlation coefficient was found between serum concentrations of CBZ and its metabolite CBZ-E, measured in two labs by different HPLC (R = 0.49 and 0.43, respectively; P < 0.001). Conclusion: We observed good correlation for estimation of CBZ and PHT concentration obtained by means the immunoassay and two different HPLC. The possibility of measurement of CBZ-E could be advantage of chromatography in comparison with immunoassay

Microdialysis of Drug and Drug Metabolite: a Comprehensive In Vitro Analysis for Voriconazole and Voriconazole N-oxide

Purpose Voriconazole is a therapeutically challenging antifungal drug associated with high interindividual pharmacokinetic variability. As a prerequisite to performing clinical trials using the minimally-invasive sampling technique microdialysis, a comprehensive in vitro microdialysis characterization of voriconazole (VRC) and its potentially toxic N-oxide metabolite (NO) was performed. Methods The feasibility of simultaneous microdialysis of VRC and NO was explored in vitro by investigating the relative recovery (RR) of both compounds in the absence and presence of the other. The dependency of RR on compound combination, concentration, microdialysis catheter and study day was evaluated and quantified by linear mixed-effects modeling. Results Median RR of VRC and NO during individual microdialysis were high (87.6% and 91.1%). During simultaneous microdialysis of VRC and NO, median RR did not change (87.9% and 91.1%). The linear mixed-effects model confirmed the absence of significant differences between RR of VRC and NO during individual and simultaneous microdialysis as well as between the two compounds (p > 0.05). No concentration dependency of RR was found (p = 0.284). The study day was the main source of variability (46.3%) while the microdialysis catheter only had a minor effect (4.33%). VRC retrodialysis proved feasible as catheter calibration for both compounds. Conclusion These in vitro microdialysis results encourage the application of microdialysis in clinical trials to assess target-site concentrations of VRC and NO. This can support the generation of a coherent understanding of VRC pharmacokinetics and its sources of variability. Ultimately, a better understanding of human VRC pharmacokinetics might contribute to the development of personalized dosing strategies

Microdialysis of Voriconazole and its N-Oxide Metabolite: Amalgamating Knowledge of Distribution and Metabolism Processes in Humans

Purpose Voriconazole is an essential antifungal drug whose complex pharmacokinetics with high interindividual variability impedes effective and safe therapy. By application of the minimally-invasive sampling technique microdialysis, interstitial space fluid (ISF) concentrations of VRC and its potentially toxic N-oxide metabolite (NO) were assessed to evaluate target-site exposure for further elucidating VRC pharmacokinetics. Methods Plasma and ISF samples of a clinical trial with an approved VRC dosing regimen were analyzed for VRC and NO concentrations. Concentration-time profiles, exposure assessed as area-under-the-curve (AUC) and metabolic ratios of four healthy adults in plasma and ISF were evaluated regarding the impact of multiple dosing and CYP2C19 genotype. Results VRC and NO revealed distribution into ISF with AUC values being ≤2.82- and 17.7-fold lower compared to plasma, respectively. Intraindividual variability of metabolic ratios was largest after the first VRC dose administration while interindividual variability increased with multiple dosing. The CYP2C19 genotype influenced interindividual differences with a maximum 6- and 24-fold larger AUCNO/AUCVRC ratio between the intermediate and rapid metabolizer in plasma and ISF, respectively. VRC metabolism was saturated/auto-inhibited indicated by substantially decreasing metabolic concentration ratios with increasing VRC concentrations and after multiple dosing. Conclusion The feasibility of the simultaneous microdialysis of VRC and NO in vivo was demonstrated and provided new quantitative insights by leveraging distribution and metabolism processes of VRC in humans. The exploratory analysis suggested substantial dissimilarities of VRC and NO pharmacokinetics in plasma and ISF. Ultimately, a thorough understanding of target-site pharmacokinetics might contribute to the optimization of personalized VRC dosing regimens

Comparison between the immunoassay and high performance liquid chromatography for therapeutic monitoring of carbamazepine and phenytoine

Objective: To investigate the correlation of the immunoassay and chromatography method for quantitative measurement of two antiepileptic drugs (AED), carbamazepine (CBZ) and phenytoin (PHT) and determination of relation between the CBZ and it\u27s metabolite carbamazepine 10,11-epoxide (CBZ-E). Additionally we investigated whether there is a difference in the determination of serum concentration of CBZ and PHT when measured in two different labs by high performance liquid chromatography (HPLC). Materials and methods: This study was carried out on 102 blood samples (72 CBZ and 30 PHT) collected from epileptic outpatients. Plasma concentrations of CBZ and PHT were determined by validated HPLC (Shimadzu and Agilent) and the CEDIA-immunoassay method. Results: The correlations of serum concentrations of CBZ between CEDIA and HPLC1 and between CEDIA and HPLC2 were good (R = 0.97 for both techniques). Even better correlation was found between concentrations of CBZ measured by the two HPLC systems (R = 0.99). Similar, for PHT, we found good correlation between CEDIA and the two systems of HPLC (HPLC1 and HPLC2, R = 0.98) and between the two systems of HPLC of R =0.98. The moderate correlation coefficient was found between serum concentrations of CBZ and its metabolite CBZ-E, measured in two labs by different HPLC (R = 0.49 and 0.43, respectively; P < 0.001). Conclusion: We observed good correlation for estimation of CBZ and PHT concentration obtained by means the immunoassay and two different HPLC. The possibility of measurement of CBZ-E could be advantage of chromatography in comparison with immunoassay

Impact of Key Components of Intensified Ceftaroline Dosing on Pharmacokinetic/Pharmacodynamic Target Attainment

Background and Objective Ceftaroline fosamil is a β-lactam antibiotic approved as a 600 mg twice daily dose (≤1 h infusion, ‘standard dosing’) or a 600 mg thrice daily dose (2 h infusion) to treat complicated skin and soft tissue infections caused by Staphylococcus aureus (minimum inhibitory concentration [MIC] 2–4 mg/L). We sought to systematically evaluate the relative impact of the three key components of the intensified dosing regimen (i.e. shortened dosing interval, prolonged infusion duration and increased total daily dose [TDD]) on the pharmacokinetic/pharmacodynamic (PK/PD) target attainment given different grades of bacterial susceptibility. Methods A population PK model was developed using data from 12 healthy volunteers (EudraCT-2012-005134-11) receiving standard or intensified dosing. PK/PD target attainment (ƒT>MIC = 35% and 100%) after 24 h was compared following systematically varied combinations of the (1) dosing interval (every 12 h [q12h]→ every 8 h [q8h]); (2) infusion duration (1 h→2 h); and (3) individual and total daily dose (400→900 mg, i.e. TDD 1200→1800 mg), as well as for varying susceptibility of S. aureus (MIC 0.032–8 mg/L). Results A two-compartment model with linear elimination adequately described ceftaroline concentrations (n = 274). The relevance of the dosing components dosing interval/infusion duration/TDD for ƒT>MIC systematically changed with pathogen susceptibility. For susceptible pathogens with MIC ≤1 mg/L, shortened dosing intervals appeared as the main driver of the improved target attainment associated with the intensified dosing regimen, followed by increased TDD and infusion duration. For less susceptible pathogens, the advantage of q8h dosing and 2 h infusions declined, and increased TDD improved ƒT>MIC the most. Conclusion The analysis calls to mind consideration of dose increases when prolonging the infusion duration in the case of low bacterial susceptibility

Towards Model-Informed Precision Dosing of Voriconazole: Challenging Published Voriconazole Nonlinear Mixed-Effects Models with Real-World Clinical Data

Background and Objectives Model-informed precision dosing (MIPD) frequently uses nonlinear mixed-effects (NLME) models to predict and optimize therapy outcomes based on patient characteristics and therapeutic drug monitoring data. MIPD is indicated for compounds with narrow therapeutic range and complex pharmacokinetics (PK), such as voriconazole, a broad-spectrum antifungal drug for prevention and treatment of invasive fungal infections. To provide guidance and recommendations for evidence-based application of MIPD for voriconazole, this work aimed to (i) externally evaluate and compare the predictive performance of a published so-called ‘hybrid’ model for MIPD (an aggregate model comprising features and prior information from six previously published NLME models) versus two ‘standard’ NLME models of voriconazole, and (ii) investigate strategies and illustrate the clinical impact of Bayesian forecasting for voriconazole. Methods A workflow for external evaluation and application of MIPD for voriconazole was implemented. Published voriconazole NLME models were externally evaluated using a comprehensive in-house clinical database comprising nine voriconazole studies and prediction-/simulation-based diagnostics. The NLME models were applied using different Bayesian forecasting strategies to assess the influence of prior observations on model predictivity. Results The overall best predictive performance was obtained using the aggregate model. However, all NLME models showed only modest predictive performance, suggesting that (i) important PK processes were not sufficiently implemented in the structural submodels, (ii) sources of interindividual variability were not entirely captured, and (iii) interoccasion variability was not adequately accounted for. Predictive performance substantially improved by including the most recent voriconazole observations in MIPD. Conclusion Our results highlight the potential clinical impact of MIPD for voriconazole and indicate the need for a comprehensive (pre-)clinical database as basis for model development and careful external model evaluation for compounds with complex PK before their successful use in MIPD