Population pharmacokinetics and probability of target attainment of meropenem in critically ill patients

Purpose: Patients admitted to intensive care unit (ICU) with Klebsiella pneumoniae infections are characterized by high mortality. The aims of the present study were to investigate the population pharmacokinetics parameters and to assess the probability of target attainment of meropenem in critically ill patients to provide information for more effective regimens. Methods: Twenty-seven consecutive patients were included in the study. Meropenem was administered as 3-h intravenous (i.v.) infusions at doses of 1–2 g every 8 or 12 h. Meropenem plasma concentrations were measured by a high-performance liquid chromatography (HPLC) method, and a population pharmacokinetics analysis was performed using NONMEM software. Meropenem plasma disposition was simulated for extended (3 h; 5 h) or continuous i.v. infusions, and the following parameters were calculated: time during which free drug concentrations were above minimum inhibitory concentration (MIC) (fT > MIC), free minimum plasma concentrations above 4× MIC (fCmin > 4× MIC), probability of target attainment (PTA), and cumulative fraction of response (CFR). Results: Gender and severity of sepsis affected meropenem clearance, whose typical population values ranged from 6.22 up to 12.04 L/h (mean ± standard deviation (SD) value, 9.38 ± 4.47 L/h). Mean Cmin value was 7.90 ± 7.91 mg/L, suggesting a high interindividual variability. The simulation confirmed that 88 and 97.5 % of patients achieved effective Cmin > 4× MIC values after 3- and 5-h i.v. infusions of meropenem 2 g × 3/day, respectively. On the contrary, the same total daily doses reached the target Cmin > 4× MIC values in 100 % of patients when administered as continuous i.v. infusions. Conclusions: Several factors may influence meropenem pharmacokinetics in ICU patients. Continuous i.v. infusions of meropenem seem to be more effective than standard regimens to achieve optimal therapeutic targets.