Aminoglycoside resistance in gram-negative bacilli during increased amikacin use. Comparison of experience in 14 United States hospitals with experience in the Minneapolis Veterans Administration Medical Center

Resistance to amikacin, gentamicin, and tobramycin was surveyed prospectively during controlled aminoglycoside usage in 14 hospitals. Following an initial baseline period (minimum, three months) during which gentamicin use predominated, gentamicin and tobramycin were placed on restrictive control, establishing amikacin as the aminoglycoside of general use (86 percent of total aminoglycoside usage). During an average of 35 months' restriction of gentamicin and tobramycin, significant reductions in gram-negative resistance to gentamicin (8.4 to 7.0 percent, p <0.001) and tobramycin (6.0 to 5.3 percent, p <0.01) were observed. The most significant decreases in resistance to gentamicin and tobramycin (p <0.001) were found for Pseudomonas aeruginosa, Klebsiella species, Serratia species, and Proteus species. Amikacin resistance among gram-negative bacilli was observed to increase marginally from 1.4 to 1.7 percent (p <0.05) during the surveillance period, primarily due to a significant increase in resistance among P. aeruginosa (3.0 to 3.9 percent, p = 0.05). These data were compared with data from a similar surveillance program at the 700-bed Minneapolis Veterans Administration Medical Center. Over a period of 54 months, both gentamicin and tobramycin resistance decreased significantly when amikacin was used (p <0.001), then increased with reintroduction of gentamicin (p <0.05), and decreased significantly with reintroduction of amikacin (p <0.001). Despite predominant amikacin use for a total of 38 months, amikacin resistance did not increase and actually decreased significantly (p <0.05) in the last 12 months.