Abstract / Summary
Background Polymyxins are used to treat nosocomial infections. Given their polycationic structure, polymyxins could lower the anion gap (AG). Purpose This study assessed the effect of polymyxins on AG in critically ill patients. Materials and Methods In this retrospective study, patients treated with polymyxins (B, E) formed the study arm. The control arm was a subset that had received meropenem prior to upgrading antibiotics to polymyxins. The AG was corrected for potassium, calcium, lactate and albumin. The change in AG before and after the first dose of antibiotics was compared using a paired t -test. Pre–post difference in AG between the antibiotics was compared using a related-samples Wilcoxon signed-rank test. Results Of the 192 patients screened, 100 patients (63 male), aged (mean, SD) 50.4 (16.5) years, who received polymyxins and 63 who received meropenem fulfilled the inclusion criteria. The mean (SD) corrected AG before and after the first dose of polymyxin was 12.7 (6.4) and 11.3 (5.3), respectively, and was significantly different (mean difference, MD, −1.37, 95% CI −2.13, −0.61). Polymyxin administration resulted in a clinically meaningful reduction of AG of >2.5 mmol/L in 38% of patients. On the other hand, the corrected AG before and after the first dose of meropenem was 12.3 (6.3) and 11.9 (5.8), respectively and similar (MD −0.43, 95% CI −1.55, 0.69). The median (IQR) difference in the pre–post AG for polymyxins (−1.46, −4.2, 1.1) and pre–post AG for meropenem (0.04, −2.8, 2.2) was significantly different ( p = .02). Conclusion Polymyxin administration is associated with a statistically significant reduction in AG after a single dose, an effect not observed with meropenem. This provides clinical evidence for a pharmacological effect that has been recognised but unquantified. Further studies are needed to quantify the change in AG with cumulative doses of polymyxin and in the setting of renal dysfunction.