Therapeutic drug monitoring of β-lactams in critically ill patients: proof of concept

The extreme pharmacokinetic behaviour of drugs sometimes observed in critically ill patients poses a significant threat to the achievement of optimal antibiotic treatment outcomes. Scant information on β-lactam antibiotic therapeutic drug monitoring (TDM) is available. The objective of this prospective study was to evaluate the practicality and utility of a β-lactam TDM programme in critically ill patients. TDM was performed twice weekly on all eligible patients at a 30-bed tertiary referral critical care unit. Blood concentrations were determined by fast-throughput high-performance liquid chromatography (HPLC) assays and were available within 12 h of sampling. Dose adjustment was instituted if the trough or steady-state blood concentration was below 4–5× the minimum inhibitory concentration (MIC) or above 10× MIC. A total of 236 patients were subject to TDM over an 11-month period. The mean ± standard deviation age was 53.5 ± 18.3 years. Dose adjustment was required in 175 (74.2%) of the patients, with 119 of these patients (50.4%) requiring dose increases after the first TDM. For outcome of therapy, 206 (87.3%) courses resulted in a positive treatment outcome and there were 30 (12.7%) treatment failures observed including 14 deaths and 15 courses requiring escalation to broader-spectrum agents; 1 course was ceased due to an adverse drug reaction. Using binomial logistic regression, only an elevated Acute Physiology and Chronic Health Evaluation (APACHE) II score (P < 0.01) and elevated plasma creatinine concentration (P = 0.05) were found to be predictive of mortality. In conclusion, further research is required to determine definitively whether achievement of optimal β-lactam pharmacodynamic targets improves clinical outcomes.