ObjectiveTo evaluate the long-term effect of a program of rotating antibiotics on the incidence of ventilator-associated pneumonia and the susceptibilities of Gram-negative bacilli responsible for ventilator-associated pneumonia.DesignProspective program for the surveillance of antibiotic susceptibilities of microorganisms responsible for ventilator-associated pneumonia.SettingAcademic, university-based, medical intensive care unit (16 beds).Subjects2,856 mechanically ventilated patients.InterventionsA new program of antibiotic use was introduced at the end of 1996 that involved the rotation of antibiotics in empirical and therapeutic use of the treatment of ventilator-associated pneumonia. The rotation concerned the &bgr;-lactam and aminoglycoside classes, with a rotation interval of 1 month. The use of antibiotics was monitored monthly. No preference was given to any particular antibiotic. In a previous study, the period before the introduction of this protocol (1995–1996) was compared with the period 2 yrs after (1997–1998): The results indicated a decreased incidence of ventilator-associated pneumonia, a lower incidence of potentially resistant Gram-negative bacilli, and increased sensitivities of Gram-negative bacilli, especiallyPseudomonas aeruginosaandBurkholderia cepacia. After 1998, we decided to continue a routine for this rotation. The long-term effect of this program was studied by comparing the incidence of Gram-negative bacilli responsible for ventilator-associated pneumonia and their susceptibilities obtained in a third period: 1999–2001. The long-term effect (5 yrs) of such a strategy—2-yr protocol period (1997–1998) and 3-yr routine period (1999–2001)—could be evaluated.Measurements and Main ResultsDuring the 7-yr study period, 2,856 patients were mechanically ventilated for >48 hrs. The incidence of ventilator-associated pneumonia remained significantly lower in period 3 (1999–2001): 23% (period 1, 1995–1996) vs. 15.7% (period 2, 1997–1998) vs. 16.3% (period 3, 1999–2001;p= .002). Late-onset ventilator-associated pneumonia occurred in 86.6% and 94% of cases, respectively, in periods 1 and 3 (p= .02). The decrease of the incidence of early-onset ventilator-associated pneumonia was statistically significant during the 7-yr study period: 13% vs. 9% vs. 5.9% (p= .02). Combined with a higher incidence of late-onset ventilator-associated pneumonia, the incidence of potentially resistant Gram-negative bacilli increased in period 3: 42.2% vs. 34.5% vs. 41.7% (nonsignificant), except forB. cepacia: 11.7% vs. 7.4% vs. 3.7% (p= .005). Nevertheless, the potential antibiotic-resistant Gram-negative bacilli were more sensitive to most of the &bgr;-lactams, especially piperacillin-tazobactam and cefepime.ConclusionsRotation of antibiotics could help to avoid ventilator-associated pneumonia. It could greatly improve the susceptibilities of the potentially antibiotic-resistant Gram-negative bacilli responsible for late-onset ventilator-associated pneumonia. This program could be applied in routine with good results 5 yrs after its introduction. Further studies, especially multiple-center trials, are necessary to confirm this result and better define the rotation type and intervals.