Polymyxin B1 Sulfate, EvoPure® is one of the polypeptide fractions in Polymyxin B Sulfate. The fatty acid group found in Polymyxin B1 Sulfate is 6-methyloctanoic acid (6-MOA); the same group found in Polymyxin B1-I Sulfate. Polymyxin B1 however, contains a L-leucine residue, rather than the L-isoleucine reside found in Polymyxin B1-I sulfate. Results from in vitro studies have shown marginal differences in MIC data when comparing the fractions.