Clinical and Microbiological Outcomes in Obese Patients Receiving Colistin for Carbapenem-Resistant Gram-Negative Bloodstream Infection

Carbapenem-resistant infections are associated with poor outcomes, and treatment options are limited. Colistin is one of few antibiotics which retain in vitro activity against carbapenem-resistant pathogens. However, despite the availability of international consensus guidelines for the dosing of polymyxins, there are limited data on the effects of dosing on clinical outcomes among obese patients with carbapenem-resistant Gram-negative bacteremia. This retrospective study evaluated whether obesity was associated with day 7 global cure rates among patients with carbapenem-resistant Gram-negative bacteremia who were treated with an ideal body weight (IBW)-based colistin dosing regimen. Secondary outcomes included microbiological cure, clinical cure, length of hospital stay, in-hospital mortality, and day 7 acute kidney injury. After screening to identify 167 patients, 77 (46.1%) and 90 (53.9%) were classified as obese and nonobese, respectively. Patient characteristics were well balanced at baseline, except that obese patients were more often female and received a higher daily dose per IBW (3.7 versus 2.9 mg/kg/day, P = 0.03). Global cure rates were similar between groups (44.2% for obese versus 55.6% for nonobese, P = 0.14). After adjusting for baseline differences, obesity was not a significant predictor of global cure (adjusted odds ratio [AOR], 0.59; 95% confidence interval [CI], 0.31 to 1.11; P = 0.10). Obesity was associated with a lower likelihood of microbiological clearance (72.7% versus 91.1%, P = 0.02). No other secondary outcome differences were observed, though each outcome was numerically worse among obese patients. Obesity was not associated with differences in global cure rates. However, the difference in microbiological clearance warrants further investigation.