The extensive use of aminoglycosides is associated with selection for resistant bacteria. Therefore, aminoglycoside use and the susceptibility of gram-negative bacteria (GNB) are monitored in our neonatal intensive care unit(NICU). We previously reported on the exclusive use of amikacin (AMK) in our nursery from 11/80 through 12/85 (Ped Inf Dis J. 6:461,1987). From 1/86 - 9/91 AMK continued to be the aminoglycoside of choice (period I). During period I, there were 5,836 admissions and AMK was used for 24,025 of 24,111 total aminoglycoside patient days (99.6%). GNB were isolated from 189 of 14,961 clinical specimens cultured during period I. 1.1% of the gram-negative isolates were amikacin-resistant and 2.7% were gentamicin-resistant.

Based on these data, gentamicin (GENT) was reintroduced as the aminoglycoside of choice in 10/91. From 10/91 - 7/95 (period II) there were 4,355 admissions and GENT was used for 23,673 of 24,363 (97.2%) aminoglycoside patient days. GNB were isolated from 108 of 5,707 clinical specimens (9.3% amikacin-resistant vs. 6.5% gentamicin-resistant).

During period I, there was no increase in resistance to AMK and the number of P. aeruginosa isolates resistant to GENT decreased significantly. To date, the reintroduction of GENT as the aminoglycoside of choice has not resulted in an increase in the number of P. aeruginosa isolates resistant to GENT. While AMK was in exclusive use, 0 of 37 E. coli and 1 of 57 Klebsiella sp. isolates were resistant to GENT. However, during period II, 3 of 40 E. coli isolates and 3 of 39 Klebsiella sp. isolates have been resistant to GENT. Although our numbers are too small to make any statistical conclusions, the extensive use of a single aminoglycoside in NICU settings is likely to result in the selection of resistant GNB. We recommend active surveillance of aminoglycoside use and monthly monitoring of the susceptibility of all gram-negative clinical isolates from the NICU as a simple way to be cognizant of changes in susceptibility to the aminoglycoside in predominant use.