The Evaluation of Meropenem Dosing Regimens Against ESBL-Producing Escherichia coli in ICU Patients Using Monte Carlo Simulation.

PURPOSE: To evaluate the optimal dosing regimens of meropenem against extended-spectrum beta-lactamase-producing Escherichia coli (ESBL E. coli) in critically ill patients with varying degrees of renal function using Monte Carlo simulation (MCS). METHODS: The MCS was performed using the minimum inhibitory concentration (MIC) data from Right Laboratory and Health Screen in Naypyitaw, Myanmar, as well as reported meropenem pharmacokinetic parameters in the target population and the pharmacokinetic-pharmacodynamic index. For each dosing regimen, 10,000 virtual patients were generated to assess the probability of target attainment (PTA) and the cumulative fraction of response (CFR). The most effective dosage regimens were determined using PTA and a CFR of 90%. RESULTS: ESBL E. coli made up 93 of the 396 clinical E. coli isolates, and they are all multidrug-resistant, with resistance to at least five antibiotic classes. The MIC50 and MIC90 were determined to be 0.25 µg/mL. The PTA was affected by five factors: creatinine clearance (CLcr), vasopressor usage, MIC, infusion time, and dosage fractionation. In patients who did not receive vasopressors, the current regimens (US-FDA and EMA) were ineffective in all renal function for MIC >0.25µg/mL. In the subset group of CLcr >80 mL/min for MIC 2µg/mL, the maximum total daily dose of 6g/day (2g q 8hr; 3hr infusion) was still ineffective, but 4g/day (1g q 6hr; 3hr infusion) achieved 98.96% PTA. Almost majority of the simulated regimens produced >90% PTA in vasopressor-dependent patients with all levels of renal function, resulting in a decreased total daily dose requirement. CONCLUSION: For high MIC (>1µg/mL) patients who do not use vasopressors and have a CLcr >80 mL/min, a combination of dosage fractionation and the extended infusion was considered as an effective technique to maximize target attainment. Neither prolonged infusion nor dosage fractionation should be explored in patients using vasopressors.

Pharmacokinetics of perioperative FVIII in adult patients with haemophilia A: An external validation and development of an alternative population pharmacokinetic model.

INTRODUCTION: Haemophilia A patients require perioperative clotting factor replacement to limit excessive bleeding. Weight-based dosing of Factor VIII (FVIII) does not account for inter-individual pharmacokinetic (PK) variability, and may lead to suboptimal FVIII exposure. AIM: To perform an external validation of a previously developed population PK (popPK) model of perioperative FVIII in haemophilia A patients. METHODS: A retrospective chart review identified perioperative haemophilia A patients at the University of North Carolina (UNC) between April 2014 and November 2019. Patient data was used to externally validate a previously published popPK model proposed by Hazendonk. Based on these validation results, a modified popPK model was developed to characterize FVIII PK in our patients. Dosing simulations were performed using this model to compare FVIII target attainment between intermittent bolus (IB) and continuous infusion (CI) administration methods. RESULTS: A total of 521 FVIII concentrations, drawn from 34 patients, were analysed. Validation analyses revealed that the Hazendonk model did not fully capture FVIII PK in the UNC cohort. Therefore, a modified one-compartment model, with weight and age as covariates on clearance (CL), was developed. Dosing simulations revealed that CI resulted in improved target attainment by 16%, with reduced overall FVIII usage by 58 IU/kg, compared to IB. CONCLUSION: External validation revealed a previously published popPK model of FVIII did not adequately characterize UNC patients, likely due to differences in patient populations. Future prospective studies are needed to evaluate our model prior to implementation into clinical practice.

After standard dosage of piperacillin plasma concentrations of drug are subtherapeutic in burn patients.

Infections are a major problem in patients with burn diseases. Mortality is high despite antibiotic therapy as studies are controversial concerning drug underdosing. The aims of this prospective, observational study were to monitor plasma concentrations of piperacillin during standard piperacillin/tazobactam treatment in 20 burn patients and 16 controls from the intensive care unit (ICU) and to optimize doses by in silico analyses. Piperacillin/tazobactam (4/0.5 g, tid) was administered over 0.5 h. Blood samples were taken at 1, 4, and 7.5 h after the end of the infusion. Free piperacillin plasma concentrations were determined. Pharmacokinetic parameters and in silico analysis results were calculated using the freeware TDMx. The primary target was defined as percentage of the day (fT>1xMIC; fT>4xMIC) when piperacillin concentrations exceeded 1xMIC/4xMIC (minimum inhibitory concentration), considering a MIC breakpoint of 16 mg/L for Pseudomonas aeruginosa. In an off-label approach, two burn patients were treated with 8/1 g piperacillin/tazobactam, 3 h qid. fT>1xMIC (55 ± 22% vs. 77 ± 24%) and fT>4xMIC (17 ± 11% vs. 30 ± 11%) were lower in burn than in ICU patients after 4/0.5 g, 0.5 h, tid. In silico analyses indicated that fT>1xMIC (93 ± 12% burn, 97 ± 4% ICU) and fT>4xMIC (62 ± 23% burn, 84 ± 19% ICU) values increase by raising the piperacillin dosage to 8/1 g qid and prolonging the infusion time to 3 h. Off-label treatment results were similar to in silico data for burn patients (84%fT>1xMIC and 47%fT>4xMIC). Standard dosage regimens for piperacillin/tazobactam resulted in subtherapeutic piperacillin concentrations in burn and ICU patients. Dose adjustments via in silico analyses can help to optimize antibiotic therapy and to predict respective concentrations in vivo. Trial registration: NCT03335137, registered 07.11.2017, retrospectively.

Population Pharmacokinetic Analysis of Busulfan in Japanese Pediatric and Adult HCT Patients.

Busulfan is the most common chemotherapy agent used in allogeneic hematopoietic cell transplant (HCT) conditioning regimens. As narrow therapeutic index and interpatient variability exists in the effectiveness and toxicity of conditioning regimens, personalizing intravenous busulfan therapy is desirable. Population pharmacokinetic-based approaches have been applied to therapeutic drug monitoring for the purpose of personalizing therapy. A population pharmacokinetic analysis with the objective of personalizing therapy in Japanese patients was conducted by integrating pediatric patient data with adult patient data. McCune's model, a 2-compartment model that includes maturation of clearance and allometric scaling of clearance and volume of distribution, was used for the analysis. McCune's model could precisely describe the Japanese data, and the estimated parameters were similar to McCune's results for non-Japanese, indicating that there are no racial differences in busulfan pharmacokinetics. Using this model, the plasma concentrations for once-daily dosing were simulated to adapt new dosage regimens for the benefit and convenience of both patients and medical staff. The predicted busulfan concentrations were within the therapeutic range.

Population pharmacokinetics of voriconazole and CYP2C19 polymorphisms for optimizing dosing regimens in renal transplant recipients.

AIMS: The aims of the present study were to characterize the pharmacokinetics of voriconazole in renal transplant recipients and to identify factors significantly affecting pharmacokinetic parameters. We also aimed to explore the optimal dosing regimens for patients who developed invasive fungal infections. METHODS: A total of 105 patients (342 concentrations) were included prospectively in a population pharmacokinetic analysis. Nonlinear mixed-effects models were developed using Phoenix NLME software. Dosing simulations were performed based on the final model. RESULTS: A one-compartment model with first-order absorption and elimination was used to characterize voriconazole pharmacokinetics. Population estimates of clearance, volume of distribution and oral bioavailability were 2.88 l·h-1 , 169.3 l and 58%, respectively. The allele frequencies of cytochrome P450 gene (CYP) 2C19*2, *3 and *17 variants were 29.2%, 5.2% and 0.5%, respectively. CYP2C19 genotype had a significant effect on the clearance. Voriconazole trough concentrations in poor metabolizers were significantly higher than in intermediate metabolizers and extensive metabolizers alike. The volume of distribution increased with increased body weight. The oral bioavailability was substantially lower within 1 month after transplantation but increased with postoperative time. Dosing simulations indicated that during the early postoperative period, poor metabolizers could be treated with 150 mg intravenously or 250 mg orally twice daily; intermediate metabolizers with 200 mg intravenously or 350 mg orally twice daily; and extensive metabolizers with 300 mg intravenously twice daily. CONCLUSIONS: Using a combination of CYP2C19 genotype and postoperative time to determine the initial voriconazole dosing regimens followed by therapeutic drug monitoring could help to advance individualized treatment in renal transplantation patients with invasive fungal infections.