Impact of diversity of antibiotic use on the development of antimicrobial resistance.
OBJECTIVE
To evaluate the impact of different antibiotic strategies on acquisition of resistant microorganisms.


METHODS
A prospective study was conducted over a 44 month period in a single ICU. Four empirical antibiotic strategies for ventilator-associated pneumonia (VAP) were sequentially implemented. Over the initial 10 months, patient-specific antibiotic therapy was prescribed; then, 4 month periods of prioritization or restriction rotation cycles of various antimicrobial agents were implemented for a total of 24 months; and, finally, during the last 10 months (mixing period) the first-line antibiotic for VAP was changed following a pre-established schedule to ensure maximum heterogeneity. Antibiotic consumption was closely monitored every month, and antimicrobial resistance patterns were regularly assessed. Antimicrobial heterogeneity was estimated using a modified Peterson index (AHI) measuring the ratios for the five most used antibiotics. Colonization by targeted microorganisms and susceptibility patterns were compared with the patient-specific period.


RESULTS
Higher diversity of antibiotic prescription was obtained during patient-specific therapy (AHI = 0.93) or mixing periods (AHI = 0.95) than during prioritization (AHI = 0.70) or restriction periods (AHI = 0.68). High homogeneity was associated with increases in carbapenem-resistant Acinetobacter baumannii (CR-Ab) [relative risk (RR) 15.5; 95%CI 5.5-42.8], extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae (RR 4.2; 95%CI 1.9-9.3) and Enterococcus faecalis (RR 1.7; 95%CI 1.1-2.9). During the restriction period, incidence of ESBL-producing Enterobacteriaceae and E. faecalis returned to patient-specific rates but CR-Ab remained higher.


CONCLUSIONS
Antibiotic prescription patterns balancing the use of different antimicrobials should be promoted to reduce the selection pressure that aids the development of resistance.
Sandiumenge
Alberto
A
Critical Care Department, Joan XXIII University Hospital, University Rovira i Virgili/Institut Pere Virgili, Tarragona 43007, Spain. asandiumenge@yahoo.com
Diaz
Emili
E
Rodriguez
Alejandro
A
Vidaur
Loreto
L
Canadell
Laura
L
Olona
Montserrat
M
Rue
Montserrat
M
Rello
Jordi
J
D040981:Acinetobacter baumannii / Q000187:drug effects / Q000302:isolation & purification; D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000302:isolation & purification; D013293:Enterococcus faecalis / Q000187:drug effects / Q000302:isolation & purification; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D018410:Pneumonia, Bacterial / Q000517:prevention & control*; D011446:Prospective Studies; D001618:beta-Lactamases / Q000032:analysis
D000900:Anti-Bacterial Agents; D001618:beta-Lactamases