Gentamicin resistance among gram-negative bacillary blood isolates in a hospital with long-term use of gentamicin.

Between 1977 and 1985, gentamicin was the only formulary aminoglycoside at the Buffalo Veterans Administration Medical Center. During this time, there was a significant increase in the amount of gentamicin purchased. Amikacin represented 11% or less of the total aminoglycoside purchased in the same period, but purchases of this agent also significantly increased. Because of this long-term use of gentamicin, a retrospective analysis of gentamicin resistance among gram-negative bacillary blood isolates was performed. The results of this review revealed no significant change in the overall incidence of gram-negative bacteremia; approximately 75% of these bacteremic episodes were hospital acquired. The mean yearly gentamicin-resistance rate of gram-negative blood isolates was 13.2% (range, 6% to 18%) with no significant change in the rate for the period reviewed. However, for certain strains there were fluctuations in the percentage of resistance from year to year, suggesting that clusters of infections due to these organisms had occurred. Bacteremic infection due to resistant organisms was a major contributor to the overall level of gentamicin resistance among blood isolates. Amikacin resistance among gram-negative blood isolates was rare. In conclusion, despite the predominant use of gentamicin there was no change in the gentamicin resistance rate among gram-negative bacillary blood isolates during a nine-year period. The rate of gentamicin resistance among blood isolates appeared to be related to outbreaks/clusters of infections due to resistant strains rather than the frequency of use of gentamicin.