A propensity score-matched analysis of the impact of minimum inhibitory concentration on mortality in patients with Pseudomonas aeruginosa bacteraemia treated with piperacillin/tazobactam.

The Clinical and Laboratory Standards Institute (CLSI) recently re-examined Pseudomonas aeruginosa minimum inhibitory concentration (MIC) susceptibility breakpoints for piperacillin/tazobactam (TZP). The objectives of this study were to analyse the impact of elevated TZP MICs (32-64 mg/L) versus lower respective MICs on P. aeruginosa bacteraemia patient outcomes. Data were gathered from a Veterans Health Administration national clinical database on P. aeruginosa bacteraemia episodes from 2007 to 2013. Patients treated with TZP were identified, comprising 53 elevated MIC episodes and 301 low MIC episodes. Propensity score matching (1:2 ratio) utilising independent variables associated with 30-day all-cause mortality was conducted to compare the outcomes of 53 elevated MIC episodes with 106 matched low MIC episodes. Independent baseline variables associated with 30-day all-cause mortality for all 354 episodes were hyperkalaemia, elevated blood urea nitrogen, elevated temperature, hypoglycaemia, lack of urinary source and thrombocytopenia. Similar 30-day all-cause mortality was found between the two propensity-matched TZP groups (elevated MIC 24.5% vs. low MIC 22.6%; P = 0.79).