Inappropriate Use of Antimicrobials at an Academic Medical Center

Background: Antimicrobial resistance is increasing and is a well-recognized public health problem. Several studies have shown an association between inappropriate antimicrobial use, emergence of resistance and adverse patient outcomes. However, data regarding comparative rates of inappropriate use of antimicrobials and correlation with outcomes in acute care, inpatient settings are lacking. Objective: To examine appropriateness of use of select antimicrobials based on institutional guidelines and correlate this with measures of patient outcome. Methods: All antimicrobial orders for vancomycin, linezolid, daptomycin, cefepime, piperacillin-tazobactam and imipenem issued at a 689-bed academic medical center between June-July 2007 were evaluated by retrospective chart review. These antimicrobials were not restricted, but institutional guidelines regarding appropriate use were available online. Any deviation from these institutional guidelines was considered inappropriate use. Pertinent patient information was collected from the medical records and analyzed with appropriate statistical tests. Results: A total of 1575 orders for vancomycin (n=698), linezolid (n=139), daptomycin (n=17), piperacillin-tazobactam (n=511), cefepime (n=144) and imipenem (n=66) were evaluated. Based on institutional guidelines for antimicrobial use, the most common appropriate indication for vancomycin was initial empiric treatment (n=397; 56.9%). A total of 53 (7.6%) vancomycin courses were inappropriate. Substantial inappropriate use of linezolid (n=70; 50.4%) and daptomycin (n=11; 64.7%) were observed; of note, appropriate use required failure or intolerance of vancomycin when used for MRSA. The most common appropriate indication for piperacillin-tazobactam (n=175, 34.2%) and cefepime (n = 39; 27.1%) was initial empiric treatment. A total of 29 (5.7%) piperacillin-tazobactam and 8 (5.6%) cefepime courses were inappropriate. Inappropriate use of imipenem was noted in 15.2% courses. The most common appropriate indication for imipenem was use in serious suspected polymicrobial infection in patients intolerant of other agents (n=18; 27.3%). Only inappropriate use of vancomycin was significantly associated with increased mortality (p<0.05) and length of stay (19.6±31.1 days for appropriate vs. 36.2±34.3 days for inappropriate; p<0.05). None of the other antimicrobials showed significant association with adverse patient outcomes.

Conclusions: Inappropriate use of antimicrobials is common without active antimicrobial stewardship intervention, despite institutional guidelines. Inappropriate use of vancomycin is associated with increased mortality and length of stay, and further evaluation is warranted. These results provide support for assertive antimicrobial stewardship efforts versus passive attempts at antimicrobial management.