Clinical and microbiologic consequences of amikacin use during a 42-month period.

In June 1980, 23% of our Pseudomonas aeruginosa isolates and 53% of our Serratia species were resistant to gentamicin and tobramycin. During a 3 1/2-year period of almost exclusive amikacin usage, we noted a fall in overall resistance of gram-negative organisms to tobramycin and gentamicin from 18.8% and 19.3% to 15.2% and 16.2%, respectively. This fall in resistance was most notable for Escherichia coli, Proteus mirabilis, and Serratia species. During this period there was no increase in amikacin resistance. Age, hospitalization, prior antibiotic therapy, and Foley catheter use were predisposing factors in acquiring amikacin-resistant organisms. Amikacin-resistant gram-negative bacilli were usually sensitive to newer penicillins or cephalosporins.