Strategies in aminoglycoside use and impact upon resistance.

Assessment of amikacin resistance over a 10-year period at our institution revealed that the number of resistant strains remained stable. Qualitatively, amikacin-resistant Enterobacteriaceae and Pseudomonas were fairly stable. There was a slight increase in amikacin-resistant Acinetobacter and staphylococci. Different factors influencing the emergence and spread of resistant hospital bacteria have been studied at different periods and compared with similar data on gentamicin-resistant strains. Transmissible plasmids, multiple mechanisms of resistance, and high levels of resistance were more frequent in gentamicin-resistant strains. In the amikacin-resistant strains, the level of resistance was 16 to 32 mg/liter with few autotransferable plasmids. A synergistic or additive effect with cephalosporins, which may be a factor in decreasing the risk of selection of the resistant strains since there is no plasmid-mediated resistance to cephalosporins, was demonstrated in Enterobacteriaceae. To control the development of aminoglycoside resistance in hospitals, it may be necessary to restrict the use of more than the one drug to which resistance is developing; to use the antibiotic at the right dosage and, when necessary, in a combination that may prevent the emergence of resistant organisms and plasmids; and to develop measures to control bacterial and R factor transmission.