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.
Critical Care Department, Joan XXIII University Hospital, University Rovira i Virgili/Institut Pere Virgili, Tarragona 43007, Spain. asandiumenge@yahoo.com
Alberto
A
Sandiumenge
Emili
E
Diaz
Alejandro
A
Rodriguez
Loreto
L
Vidaur
Laura
L
Canadell
Montserrat
M
Olona
Montserrat
M
Rue
Jordi
J
Rello
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