Stability of warfarin sodium flavoured preservative-free oral liquid formulations

This study was designed to assess the physicochemical stability of warfarin sodium liquid formulations stored at room temperature and under refrigeration.

Formulations of warfarin sodium 1mg/mL were prepared from either powder or tablets dispersed in mixture containing deionised water, glycerin, sodium phosphate and strawberry alcohol-free concentrate flavour and stored in amber glass bottles at 25°C and 4°C. Stability indicating high-performance liquid chromatography assay procedure was used to analyse the concentration of the drug at the time of preparation and on days 7, 14, 21, 30, 45, 60 and 90. Changes in colour, taste and pH, as well as visual evidence of precipitation, were assessed for physicochemical instability.

Between day 0 and day 90, the pH of the powder and tablet formulations stored at 25°C decreased by -1.40 units and -1.16 units, respectively. There were minor changes in pH for both formulations stored at 4°C. The formulation from powder stored at 25°C and 4°C maintained at least 90% of the initial warfarin concentration for 30 days and 45 days, respectively. The formulation from tablets stored at 25°C and 4°C maintained at least 90% of initial warfarin concentration for 21 days and 30 days, respectively.

Warfarin sodium in flavoured preservative-free formulation from powder is recommended and stable in amber glass bottles for at least 30 days stored at 25°C and 45 days stored at 4°C.