In colistin, five of the terminal amino groups of the α-aminobutyric acid fragment may be readily alkylated. In colistimethatesodium, pentasodium colistinmethanesulfonate,sodium colistimethanesulfonate (Coly-Mycin M), the methanesulfonate radical is the attached alkyl group, and asodium salt may be made through each sulfonate. This providesa highly water-soluble compound that is very suitablefor injection. In the injectable form, it is given intramuscularlyand is surprisingly free from toxic reactions comparedwith polymyxin B. Colistimethate sodium does not readilyinduce the development of resistant strains of microorganisms,and there is no evidence of cross-resistance with thecommon broad-spectrum antibiotics. It is used for the sameconditions mentioned for colistin.
