A Simple HPLC Method for the Separation of Colistimethate Sodium and Colistin Sulphate

Colistin, also known as polymyxin E, a polymyxin antibiotic, comprised of colistin E1 and colistin E2, has good inhibitory effect for pathogen infection [1,2]. The characteristic lariat structure of colistin E1 was proven necessary for antimicrobial activity [3]. Since the sulfate polymyxin compounds were separated from different types of bacillus polymyxa in 1947, they have been tested by vitro experiments. In P.aeruginosa, it has been proven that high-level resistance can arise from adaptation in the presence of colistin E2 in vitro [4,5]. There is cross-resistance between colistin E1 and colistin E2 [6]. However its application has not been popularized because of its toxicity and other side effects. But the toxicity and side effects of colistimethate sodium (CMS) will be depressed without drug action diminishing. Colistimethate sodium is synthesized by treating the primary amine groups of the α, γ-diaminobutyric acid residues in colistin with formaldehyde followed by sodium bisul-fite [7]. There are two main compositions in the product which are colistimethate sodium E1 (CMS E1) and colistimethate sodium E2 (CMS E2). The structures of colistin sulphate and CMS are shown in Figure 1.