CHEMICAL-STABILITY OF POLYMYXIN-B IN AQUEOUS-SOLUTION

Chromatographic separations of the components of polymyxin B sulphate are reported and it is shown that the separations are such that two of the three major components detected are specific for the intact drug in the presence of chemical decomposition products. The specificity of the separations with respect to other antibacterials, propamidine, di bromopropamidine and trimethoprim is also reported. Validation of the stability indicating assay based on this separation is described. Rate constants for the decomposition of polymyxin at various temperatures between 32 and 52 degrees C and in solutions of different pH values fr om 2.0 to 10.3 are determined and the t(90) value at pH 7 and 4 degree s C is estimated.