An evaluation of the susceptibility patterns of gram-negative organisms isolated in cancer centres with aminoglycoside usage.

This study in 12 cancer treatment centres across the United States was designed to evaluate the potential for increased resistance to amikacin with unrestricted use. An initial 3-month baseline period during which the use of amikacin was restricted and that of tobramycin and gentamicin unrestricted was followed by a period of at least 12 months when amikacin was the primary aminoglycoside. Resistance of Gram-negative bacilli to these aminoglycosides from hospitalized patients was monitored and compared for the two periods. Amikacin usage increased from a mean of 20.1% to a mean of 83.9% of aminoglycoside patient-days. A reduction in the use of tobramycin and gentamicin were observed with means of 66.1 and 10%, and 13.9 and 6.1%, respectively for the two periods. Resistance to amikacin was 0.85% at baseline and 1.3% at end-point which was not clinically significant (P = 0.614). Baseline resistance was 6.5 and 7.6%, while final resistance was 2.6 and 4.8%, respectively for tobramycin (P = 0.001) and gentamicin (P = 0.052).