Polymyxin E1 Sulfate

Colistin (polymyxin E) is a cyclic polypeptide with a potent bactericidal action against most gramnegative bacilli. When used parenterally, polymyxins should be given with great care as they have a very small safety range, and easily induce neurotoxicity and nephrotoxicity. A dose of 39.5mg/kg body weight colistin sulphate injected subcutaneously induced rapid (within 1 to 3 h) mortality in young ostriches. Clinical signs of apathy, lethargy and hypotonia indicative of neurotoxicity of the compound were observed. At postmortem, vascular congestion of brain vessels was seen while, on histology, severe acute oedema was present in the epicardium and the intestinal serosa. Congestion of villi, swelling and vacuolization of the plexus ofAuerbach, as well as intermuscular and perivascular oedema of the heart, were also observed. In view of our observations in ostriches and in other species studied, a dose of >5mg/kg body weight polymyxin E is not considered safe for parenteral administration in ostriches.

A method of micellar electrokinetic chromatography capillary (MECC) has been established for separating polymyxins E1 and E2 in polymyxin E sulfate and determining the contents of E1 and E2. Several factors including the running voltage, the type of surfactant, concentrations of Brij-35 (polyoxyethylene glycol dodecyl ether), NaCl solution and acetonitrile, pH of phosphate were investigated. Under the optimum conditions (10 kV running voltage, phosphate buffer solution (0.01 mol/L, pH 4.1) containing 30 mmol/L Brij-35, 5% (v/v) acetonitrile, 0.167 mol/L NaCl), E1 and E2 were separated with the resolution of 1.94. The contents of E1 and E2 in polymyxin E sulfate were 67% and 32%, respectively. As an example, the relative standard deviations of the intra-assay and inter-assay of polymyxin E1 on the plate number and peak area were less than 5%. The method is simple, rapid, accurate, and reproducible.

A methodology following International Cooperation on Harmonization for Veterinary Products (VICH) guidelines for the stability evaluation of colistin sulfate in a nonaqueous suspension pharmaceutical dosage form for veterinary use (via their drinking water) is described. This method monitors the percentage of colistin sulfate during the stability study of the preparation in drinking water and establishes the shelf life of the final product by a new high-performance liquid chromatography method which was developed and validated for the simultaneous determination of colistin sulfate [colistin A (Polymixin E1) and colistin B (Polymixin E2)] and methylparaben (Nipagin) using a diode array detector (DAD). The method uses a Kromasil C18 column and isocratic elution. The mobile phase consisted of an acetonitrile-sodium sulfate anhydrous solution (25 + 75) pumped at a flow rate of 1.5 mL/min. The DAD was set at 215 nm. The validation study was carried out according to the VICH guidelines in order to prove that the new analytical method meets the reliability characteristics, which include the fundamental criteria for validation: selectivity, linearity, precision, accuracy, and sensitivity. The method was applied during the quality control or stability studies of the suspension dosage form in order to quantify the drug (colistin) and preservative, and proved to be suitable for rapid and reliable quality control.