Development of a liquid chromatographic method for ear drops containing neomycin sulphate, polymyxin B sulphate and dexamethasone sodium phosphate.

Two liquid chromatographic methods were developed to analyse ear drops containing neomycin sulphate, polymyxin B sulphate and dexamethasone sodium phosphate. This formulation will be described in the Belgian National Formulary. Since neomycin, an aminoglycoside antibiotic, has no UV chromophore and pre or post column derivatization is complicated, pulsed electrochemical detection on a gold electrode was chosen to determine neomycin. Polymyxin B sulphate and dexamethasone sodium phosphate do have a UV chromophore. So, a single LC method with UV detection was developed for the determination of polymyxin B sulphate and dexamethasone sodium phosphate. The sample pretreatment is simply done by diluting the formulation with water. For each method, the influence of the different chromatographic parameters on the separation, the interference of other active compounds and excipients, the repeatability and the linearity were investigated. Finally, the content of the actives in the formulation was studied at 0, 2, 4, 6, and 8 weeks.