Polymyxin B3 sulfate is an individual fraction found in the antibiotic mixture polymyxin B sulfate. Polymyxin B3 sulfate is differentiated from its counterpart fractions by the presence of an octanoic fatty acid moiety. Results from in vitro studies have shown marginal differences in MIC data when comparing the fractions. Kassamali, et al. used polymyxin B1, polymyxin B2, polymyxin B3, and polymyxin B1-I to test for synergistic and antagonistic effects against various Gram-negative organisms.Read more here: "Microbiological Assessment of Polymyxin B Components Tested Alone and In Combination" Lim et al. used polymyxin B1, B2, B3, and B1-I from TOKU-E to study the stability of each compound in saline, dextrose, and saline/dextrose infusion solutions. "Physicochemical stability study of polymyxin B in various infusion solutions for administration to critically Ill patients."