A suspension comprising of the three antibiotic substances amphotericin B, colistin sulfate andtobramycin sulfate is often used in clinical practice for the selective decontamination of the digestivetract of patients in intensive care. Since no detailed procedures, specifications or stability data are avail-able for manufacturing this suspension, there may be discrepancies regarding formulation and stabilityof suspensions prepared in different pharmacies. The aim of this work is to develop a standardized for-mulation and to determine its stability under defined storage conditions. This would help guarantee thatall patients receive the same preparation, therefore ensuring similar efficacy and improved safety. Thefirst step in this process is to develop the required analytical tools to measure the content and purity ofthe drug substances in this complex mixture. In this paper, the development and validation of these toolsas well as the development of the drug suspension formulation is described. The formulation comprisesof Ampho-Moronal®-Suspension (Dermapharm) and a buffered, preservated aqueous solution of colistinsulfate and tobramycin sulfate. Two simple, well established high-performance liquid chromatography(HPLC) methods in the European Pharmacopoeia (EP) for impurity profiling of the two active ingredientsamphotericin B and colistin sulfate were combined with a newly developed sample extraction proce-dure for the suspension. Sufficient selectivity and stability-indicating power have been demonstrated.Additionally, a new robust routine method was developed to determine possible degradation productsof tobramycin sulfate in the investigated suspension. The specificity, precision, accuracy and linearity ofthe analytical procedures were demonstrated. The recovery rate was in the range of 90–110%. The pre-cision results for the calculated impurities showed variation coefficients of