Learning Objectives: Currently rates of carbapenem resistance at our institution is about 50% requiring the use of polymyxin B in many cases. Despite its efficacy the use of this agent is limited due to toxicities, including nephrotoxicity. Therefore, we sought to retrospectively evaluate the incidence of acute kidney injury (AKI) in patients treated with 24 hour continuous infusion of polymyxin B therapy.

Methods: Adult patients treated with polymyxin B therapy by continuous infusion for at least 48 hours from January 2014 to December 2015 were evaluated. Patients with a baseline CrCl < 10mL/min or on dialysis were excluded. Only the first course of polymyxin B was considered. The incidence of AKI was determined based on the RIFLE criteria.

Results: A total of 31 patients were included in this cohort, of which 12 patients (38.7%) were admitted to an intensive care unit (ICU). ICU patients had a mean age of 71, 58% were female, and the mean APACHE II score was 22.5. The mean hospital length of stay was 41.2 ± 22.7 days and the baseline serum creatinine was 1.04mg/dL ± 0.9. The use of nephrotoxins and vasopressors was high among ICU patients (58% and 42%). ICU culture results (94%) were positive for XDR Acinetobacter baumannii (50%) and Klebsiella pneumoniae (50%), with 58% of the isolates resistant to polymyxin B. The duration of therapy in ICU patients was 14.3 ± 9.9 days and the average daily dose was similar in both ICU and non-ICU patients (15,499 units/kg vs. 14,053 units/kg; p=0.36). The overall incidence of AKI in this cohort was 35.5%, 50% in ICU patients and 26.3% in non-ICU patients (p=0.18). The mean time to onset of AKI was 4 days earlier in ICU patients (p=0.26). Overall hospital mortality was 38.7%, 66.7% in ICU patients and 21% in non-ICU patients (p=0.02).

Conclusions: The incidence of AKI with continuous infusion of polymyxin B therapy appears to be elevated in this cohort of critically ill patients. Further studies comparing the incidence of AKI with different methods of administration, including intermittent dosing, may help guide an effective and safer method of providing polymyxin B.