RESUMEN
Gram-negative bacterial isolates from patients in the intensive care units and their antibiotic susceptibilities together with the consumption of antibiotics in these units were studied. 10,494 grams of antibiotics were consumed in these units, equivalent to 605 days of treatment per 100 hospital discharges. Ampicillin, ceftriaxone, ceftazidime and gentamicin were among the most commonly used drugs. The most frequent isolates were P. aeruginosa, followed by Klebsiella spp., E. coli, Serratia spp., Acinetobacter spp., and Enterobacter cloacae. The most effective antibiotics were ciprofloxacin and imipenem, inhibiting 94% and 92% of the strains, respectively. Only 36% of the strains were susceptible to ceftriaxone, 40% to cefotaxime and 78% to ceftazidime. Resistance to cephalosporins was mostly encountered with Klebsiella spp., E.cloacae and Acinetobacter spp. Piperacillin and piperacillin/tazobactam inhibited 73% and 82% of strains, respectively. Aminoglycosides' activity was similar to that of piperacillin/tazobactam. Some E. cloacae, Serratia spp. and Acinetobacter spp. were multi-resistant to cephalosporins, aztreonam and piperacillin/tazobactam. 41% of Klebsiella spp. were resistant to cephalosporins and aztreonam, probably due to ESBLs. Imipenem resistance occurred with Pseudomonas spp., Acinetobacter spp. and S. multophilia. Overuse of antibiotics, particularly cephalosporins could be behind this high rate of drug resistance. Rational prescribing of antibiotics should be encouraged through educational programmes, surveillance and audit