Tigecycline is a glycylcycline often used in critically ill patients as the antibiotic of last resort. The pharmacokinetics (PK) of tigecycline in intensive care unit (ICU) patients can be affected by severe pathophysiological changes so that standard dosing might not be adequate. The aim of this study was to describe population PK of high-dose tigecycline in patients with sepsis or septic shock and evaluate the relationship between individual PK parameters and patient covariates. The study population consisted of 37 adult ICU patients receiving a 200-mg loading dose of tigecycline followed by multiple doses of 100 mg every 12 h. Blood samples were collected at 0.5, 2, 4, 8, and 12 h after dose administration. A two-compartment model with interindividual (IIV) and interoccasion (IOV) variability in PK parameters was used to describe the concentration-time course of tigecycline. The estimated values of mean population PK parameters were 22.1 liters/h and 69.4 liters/h for elimination and intercompartmental clearance, respectively, and 162 liters and 87.9 liters for volume of the central and peripheral compartment, respectively. The IIV and IOV in clearance were less than 20%. The estimated values of distribution volumes were different from previously published values, which might be due to pathophysiological changes in ICU patients. No systematic relationship between individual PK parameters and patient covariates was found. The developed model does not show evidence that individual tigecycline dosing adjustment based on patient covariates is necessary to obtain the same target concentration in patients with sepsis or septic shock. Dosing adjustments should be based on the pathogens, their susceptibility, and PK targets.

No abstract

Standard dosing of caspofungin in critically ill patients has been reported to result in lower drug exposure, which can lead to subtherapeutic AUC0–24/MIC ratios. The aim of the study was to investigate the population pharmacokinetics of caspofungin in a cohort of 30 ICU patients with a suspected invasive fungal infection, with a large proportion of patients requiring extracorporeal therapies including ECMO and CRRT. Caspofungin was administered as empirical antifungal therapy 70 mg i.v. on the first day and 50 mg i.v. on the consecutive days once daily and the concentrations were measured after 3 subsequent doses. Population pharmacokinetic data were analysed by nonlinear mixed-effects modeling. The pharmacokinetics of caspofungin was described by 2-compartment model. A particular drift of individual CL and V1 values with time was discovered and described by including three separate typical values of CL and V1 in the final model. The typical CL values at day one, two and three were 0.563 L/h (6.7 %RSE), 0.737 L/h (6.1 %RSE) and 1.01 L/h (9.1 %RSE), respectively. The change in parameters with time was not explained by any of the recorded covariates. Increasing clearance with subsequent doses was associated with a clinically relevant decrease in caspofungin exposure (>20%). The use of ECMO, CRRT, albumin concentration, and other covariates did not significantly affect caspofungin pharmacokinetics. Additional pharmacokinetic studies are urgently required to assess the possible lack of acquiring steady-state and suboptimal concentrations of the drug in critically ill patients.

The ionization pattern of tocochromanols in the APCI source is problematic and should be further investigated. Modelling methodology for response improvement presented in this study can be applied in similar studies.

The purpose of this work was i) to develop a population pharmacokinetic (PK) and pharmacodynamic (PD) model of dexmedetomidine (DEX) in New Zealand White rabbits, ii) to investigate the influence of the age and weight of the animals on the model parameters, and iii) to assess the linearity of DEX PKs in the examined dose range. This was a prospective, crossover study, using a total of 18 New Zealand White rabbits. DEX was administered as a single intravenous bolus injection in the doses from 25 to 300 μg kg−1. Each New Zealand White rabbit was given the same dose of drug in its three developmental stages. To determine the DEX PK, seven blood samples were taken from each animal. The pedal withdrawal reflex was the PD response used to assess the degree of sedation. Nonlinear mixed effects modelling was used for the population PK/PD analysis. The typical value of elimination clearance was 0.061 L min−1 and was 35% higher in younger New Zealand White rabbits compared with older animals. The PK of DEX was linear in the examined concentration range. Age‐related changes in sensitivity to DEX were not detected. The results suggest that due to the pharmacokinetics, younger animals will have lower DEX concentrations and a shorter duration of sedation than older animals given the same doses of DEX per kg of body weight.