Background Antimicrobial resistance is a growing problem worldwide. Excessive and inappropriate use of antibiotics constitutes an important risk factor in the development of bacterial resistance, so discriminating use of antimicrobial agents remains the key for minimising this problem.

Purpose To analyse the relationship between the evolution of consumption of piperacillin–tazobactam and the variation in susceptibility patterns of gram negative microorganisms and the number of isolates of pathogens with low prevalence, in the intensive care unit of a tertiary hospital.

Material and methods We calculated defined daily doses per 1000 patient days (DDD/1000 PD) of piperacillin–tazobactam for every year between 2011 and 2015, according to ATC/DDD-WHO Nordic Council methodology. Microbial susceptibility to this antibiotic was studied for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Enterobacter spp. We recorded the number isolates of extended spectrum beta lactamase (ESBL) producing both E coli and K pneumoniae, Enterobacter spp and Stenotrophomonas spp. Susceptibility was determined by Microscan automation system (Siemens Health Care Spain). These data were correlated with DDD/1000e of piperacillin–tazobactam through the correlation coefficient r of Pearson (level of bilateral significance=0.05). Analysis of the results was performed using SPSS Statistics IBP-19 version.

Results DDD/1000 PD for piperacillin–tazobactam were 170.1/189.9/208.9/216.3/229.7 in 2011/2012/2013/2014/2015, respectively. Susceptibilities to piperacillin–tazobactam in these years were: 89.6%/82%/73%/81%/87% (for E coli); 75%/74%/83%/85%/77.8% (for K pneumoniae); 88.7%/70%/85%/75%/86% (for P aeruginosa) and 80%/78%/71%/74%/68.3% (for Enterobacter spp). The number of microorganisms of ESBL isolates were 24/52/38/29/20, the number of isolates of Stenotrophomonas spp 5/0/27/36/36 and Enterobacter spp 2/81/45/43/82 between 2011 and 2015. The correlation coefficients of the analysis were: r=−0.307 for E coli (p=0.616), r=0.804 for K pneumoniae (p=0.101), r=−0.043 for P aeruginosa (p=0.946); r=−0.932 for Enterobacter spp (p=0.021); r=−0.272 for ESBL microorganisms (p=0.658), r=0.895 for Stenotrophomonas spp (p=0.040) and r=0.618 for Enterobacter spp (p=0.267).

Conclusion The increased consumption of piperacillin–tazobactam was correlated with decreased susceptibility of Enterobacter spp to it and with a higher number of isolates of Stenotrophomonas spp. No influence on other microorganisms analysed was detected. This could be because of a delay in the impact of consumption on the ecological impact, which could be revised in subsequent studies.

References and/or acknowledgements WHO Collaborating Centre for Drug Statistics Methodology. ATC-Index with DDDs.

No conflict of interest