Polymyxin B Sulfate is a cyclic polycationic peptide antibiotic that binds to anionic lipids. It is also a selective inhibitor of protein kinase C. Other direct and indirect biological effects of polymyxin B include induction of apoptosis, blocking the effect of endotoxins, modulation of K+-ATP channels, inhibition of the effect of phorbol ester–stimulated superoxide release, inhibition of sarcoplasmic reticulum Ca2+-ATPase, and inhibition of insulin secretion. Polymyxin B is also reported to be a potent inhibitor of calmodulin (C23693), with an IC50 of 80 nM in the presence of 500 µM Ca2+.

USP grade, nonsterile, crystalline