A stability study of amphotericin B, colistin and tobramycin in a hydrophilic suspension commonly used for selective decontamination of the digestive tract by HPLC and in vitro potency measurements.

OBJECTIVES

A suspension for oral use which consists of three non-absorbable antibiotics (amphotericin B, colistin and tobramycin) is often used in clinical practice for the selective decontamination of the digestive tract (SDD) of patients in intensive care. Such a therapy is a preventive tool to minimise the risk of pneumonia and bacteraemia in intubated patients. The administration and the treatment results are controversially discussed. One limiting factor for a unique SDD treatment in the hospitals is a lack of adequate data regarding batch formula and stability for such a formulation. Since no detailed procedures, specifications or stability data are available for manufacturing this formulation there may be discrepancies regarding formulation and stability of suspensions prepared in different pharmacies. The aim of this research was to collect the physicochemical and microbiological stability data of a developed, stable standard formulation under defined storage conditions. The effectiveness of the SDD suspension should be preferably proven over a long period. This would help guarantee that all patients receive the same preparation, therefore, ensuring similar efficacy and improved safety.

METHODS

An adequate formulation composed of the registered, marketed medicinal product (Dermapharm AG, Germany) and a buffered, preserved aqueous solution of colistin and tobramycin both as sulfates has been developed. A stability study has been performed on two batches of the formulation. During the storage, samples were taken and compatibility was verified by physicochemical and microbiological testing in stability-indicating terms of colour, odour, flavour, pH, chemical and microbiological purity as well as in vitro potency. The test methods were built and tailored to be suitable, reliable and precise for the test needs.

RESULTS

The results show the physicochemical and microbiological stability of the described formulation for defined storage conditions.

CONCLUSIONS

A standardised formulation with a proven stability for at least 6 months under fridge (5°C±3°C) conditions for the SDD of patients in intensive care was established.