Background and Importance Therapeutic drug monitoring (TDM) of ertapenem is recommended in critically ill patients (CIP) to address their variability in exposure because of its time-dependent, highly protein bound and hydrophilic characteristics.

Aim and Objectives To describe efficacy and safety in a CIP after optimising the posology of ertapenem.

Material and Methods A case report in a CIP treated with ertapenem is described. Data were collected from electronic medical records and ertapenem concentrations were measured by high-performance liquid chromatography.

Results A 35-year-old men with a body mass index (BMI) of 32.6kg/m² with a surgical wound culture positive for AmpC-producing Klebsiella pneumoniae was started ertapenem 1g q24h (minimum inhibitory concentration (MIC) of 0.38 for Klebsiella). Three days after initiation, ertapenem plasma concentrations were determined. In that moment, his creatinine value was 0.21mg/dL with a glomerular filtration rate (GFR) of 700ml/min by the Cockroft-Gault formula, and his albumin value was 2.9mg/dL. Ertapenem serum concentrations were 1.65mcg/ml (total drug); 0.16mcg/ml of unbound fraction (fu), considering a protein binding of 90%. Fu should be above the MIC, ideally 4 times the MIC (≥1,52 mcg/ml), and fever persisted, so in agreement with the medical team the dosage was optimise to 0.5g q12h considering its time-dependent pharmacokinetics. Two days after posology optimisation, the patient became afebrile, and 6 days after being with the new regimen, blood concentrations were remeasured resulting in 6.97mcg/mL, and a fu of 0.69 mcg/mL, which is 1.8 times the MIC. Despite not having reached fu of 4 times the MIC, given that the patient remained afebrile after dose optimisation and as a precaution for not reaching toxic concentrations due to an increase in the total daily dose, the 0.5g q12h dosage was maintained for another week, when the infection was solved and the antibiotic discontinued.

No adverse effects related to ertapenem were reported.

Conclusion and Relevance The optimisation of ertapenem posology, changing the frequency without increasing the total daily dose, allowed increasing ertapenem concentrations and improved the clinical outcome of a CIP with augmented renal clearance, low albumin and high BMI, characteristics that may lower ertapenem concentrations, without decreasing the safety of the drug.

Conflict of Interest No conflict of interest