Data were collected daily in the ICU regarding the presence of mechanical ventilation, all intravascular catheters, and the presence of a urinary catheter. The dates antibiotics were started and stopped were collected. Antibiotics were divided prospectively into three broad groups (first, second, and third line) according to empirical usage in the ICU. First-line antibiotics were defined as amoxicillin, ampicillin, amoxicillin/clavulanic acid, azactam, azithromycin, cefamazine, cefuroxime, ciprofloxacin, clindamycin, cloxacillin, metronidazole, gentamicin, levofloxacin, penicillin, piperacillin, rifampicin, co-trimoxazole, and tobramycin. Second-line antibiotics were defined as amikacin, cefepime, cefotaxime, cefotetan, ceftazidime, ceftriaxone, and piperacillin/tazobactam. Third-line antibiotics were defined as colistin, ertapenem, imipenem, linezolid, meropenem, ampicillin/sulbactam, and vancomycin.