Introduction of Ertapenem into a Hospital Formulary: Effect on Antimicrobial Usage and Improved In Vitro Susceptibility of Pseudomonas aeruginosa

Abstract

After ertapenem was added to the formulary of a 344-bed community teaching hospital, we retrospectively studied its effect on antimicrobial utilization and on the in vitro susceptibility of various antimicrobial agents against Pseudomonas aeruginosa. Three study periods were defined as preintroduction (months 1 to 9), postintroduction but before the autosubstitution of ertapenem for ampicillin-sulbactam (months 10 to 18), and after the policy of autosubstitution (months 19 to 48) was initiated. Ertapenem usage rose slowly from introduction to a range of 36 to 48 defined daily doses/1,000 patient days (DDD) with a resultant decrease in ampicillinsulbactam usage due to autosubstitution. Imipenem usage peaked 6 months after the introduction of ertapenem and started to decline coincidently with the increased use of ertapenem. During the second period, imipenem usage decreased (slope ‫؍‬ ؊1.28; P ‫؍‬ 0.002). Prior to the introduction of ertapenem, the susceptibility of P. aeruginosa to imipenem increased from 61 to 81% at month 7 but then decreased slightly to 67% at month 9. After the introduction of ertapenem, susceptibility continued to increase; the increasing trend was significant (slope ‫؍‬ 1.74; P < 0.001). In the third period, the median susceptibility (interquartile range) was 88% (82 to 95%). This change appeared related to decreased imipenem usage. For every unit decrease in the monthly DDD of imipenem, there was an increase of 0.38% (P ‫؍‬ 0.008) in the susceptibility of P. aeruginosa to imipenem in the same month. Ertapenem was effective in our antimicrobial stewardship program and may have helped improve the P. aeruginosa antimicrobial susceptibility to imipenem by decreasing the unnecessary usage and selective pressure of antipseudomonal agents.

Mathematical Model To Quantify the Effects of Risk Factors on Carbapenem-Resistant Acinetobacter baumannii

“…In contrast to findings of previous studies in Pseudomonas aeruginosa (12,24,25), we found that ertapenem consumption was associated with a rise in CRAB prevalence. Ertapenem is presumed to have a lower potential to induce resistance in P. aeruginosa or A. baumannii, given the intrinsic resistance in both organisms.…”

Impact of an Antimicrobial Stewardship Initiative on Ertapenem Use and Carbapenem Susceptibilities at Four Community Hospitals

“…In a long-term study, despite an increasing use of ertapenem over a 9 year period, no association was found between ertapenem and changes in pseudomonal susceptibility to carbapenems [37]. Other studies have reported an increased susceptibility to imipenem among P. aeruginosa after introduction of ertapenem, presumptively due to decrease in group 2 carbapenems [35,36]. While the present study detected an overall decrease in carbapenem non-susceptible Pseudomonas isolates in the postintervention period, whether this is a direct impact of ertapenem or through indirect changes in other antimicrobials is unknown.…”

“…[35][36][37]. In many instances, these investigations reported improved susceptibilities of Enterobacteriaceae and Pseudomonas spp.…”

Carbapenem stewardship: positive impact on hospital ecology

“…15 Goldstein et al reported that adding ertapenem to the formulary in a 344-bed community hospital was an effective antimicrobial management tool. 7 Apisarnthanarak et al demonstrated that conducting surveillance and implementing prescribing policies resulted in reductions in antibiotic consumption and resistance in a tertiary care hospital in a developing country.…”