Reduction in fluoroquinolone use following introduction of ertapenem into a hospital formulary is associated with improvement in susceptibility of Pseudomonas aeruginosa to group 2 carbapenems: a 10-year study

Abstract

We examined the effect of the addition of ertapenem to our hospital formulary on the resistance of nosocomial Pseudomonas aeruginosa to group 2 carbapenems (imipenem, meropenem, and doripenem). This was a retrospective, observational study conducted between 1 January 2000 and 31 January 2009 at a large, tertiary-care hospital. Autoregressive integrated moving average (ARIMA) regression models were used to evaluate the effect of ertapenem use on the susceptibility of Pseudomonas aeruginosa to group 2 carbapenems as well as on the use of the group 2 carbapenems, ciprofloxacin, and other antipseudomonal drugs (i.e., tobramycin, cefepime, and piperacillin-tazobactam). Resistance was expressed as a percentage of total isolates as well as the number of carbapenem-resistant bacterial isolates per 10,000 patient days. Pearson correlation was used to assess the relationship between antibiotic use and carbapenem resistance. Following the addition of ertapenem to the formulary, there was a statistically significant decrease in the percentage of Pseudomonas aeruginosa isolates resistant to the group 2 carbapenems (P = 0.003). Group 2 carbapenem use and the number of carbapenem-resistant Pseudomonas aeruginosa isolates per 10,000 patient days did not change significantly over the time period. There was a large decrease in the use of ciprofloxacin (P = 0.0033), and there was a correlation of ciprofloxacin use with the percentage of isolates resistant to the group 2 carbapenems (ρ = 0.47, P = 0.002). We suspect that the improvement in susceptibility of Pseudomonas aeruginosa to group 2 carbapenems was related to a decrease in ciprofloxacin use.

Fig. 1.

Ertapenem, group 2 carbapenem (imipenem, meropenem, and doripenem), and ciprofloxacin use in defined daily doses per 1,000 patient days (DDD/1000 PD) and percentage of Pseudomonas aeruginosa isolates resistant to the group 2 carbapenems over the 10-year time period. Ciprofloxacin use and percent carbapenem-resistant P. aeruginosa isolates were plotted using a 5-quarter moving-average transformation. Time increments are in quarters. Ertapenem was added to the hospital formulary in April 2002.

Fig. 2.

Use of antipseudomonal drugs over the 10-year study period. Usage is defined in daily doses per 1,000 patient days (DDD/1000 PD). Data were plotted using a 5-quarter moving-average transformation.

Fig. 3.

The percentage of carbapenem-resistant Pseudomonas aeruginosa isolates plotted versus the use of ciprofloxacin in defined daily doses per 1,000 patient days. There was a correlation of ciprofloxacin use with the percentage of carbapenem-resistant Pseudomonas aeruginosa isolates (ρ = 0.47; P = 0.0020).