Colistin associated with higher rate of AKI than polymyxin B in critically ill

Critically ill patients who were given intravenous colistin had a greater incidence of acute kidney injury (AKI) than those given polymyxin B, a study found.

In a retrospective cohort study, researchers examined data on 67 adult patients who received intravenous polymyxin B (PB) between January 2008 and June 2009 and 106 patients who received colistin from January 2009 through June 2010, both for at least 72 hours. Patients with normal renal function had PB dosed at 15,000 to 25,000 units/kg per day as a continuous infusion over 24 hours. Colistin was dosed at 5 mg/kg of ideal body weight per day or actual body weight or as a fixed dose of 150 mg every 12 hours. RIFLE (risk, injury, failure, loss and end-stage kidney disease) criteria were used to define nephrotoxicity and to evaluate the severity of acute renal failure. Both agents were mostly used to treat multidrug-resistant Pseudomonas aeruginosa andAcinetobacter baumannii infections, and most patients were in the ICU.

The mean treatment duration was 11.7 days for colistin and 12.5 days for PB (P=0.66). Nephrotoxicity developed in 60.4% of colistin patients and 41.8% of PB patients (P=0.02). Among those who developed it, the difference in time to peak serum creatinine wasn't significantly different between groups. Most patients who developed acute renal failure fell into the reversible kidney injury category. Only one patient progressed to end-stage renal disease (from the colistin group). Results were published online July 9 in Clinical Infectious Diseases.

The study is limited by its retrospective nature and small sample size and by the fact that the drugs were studied in two different time periods, so potential variations in practice could have affected results. Also, dose adjustments or drug discontinuations due to acute renal failure weren't captured. Overall, the study adds more strength to previous results showing a temporal relationship between using these agents and development of nephrotoxicity, the authors wrote, and patients who take them should be closely monitored.