Objectives The aim of this study was to evaluate the effect of storage conditions on the shelf life of liquid pharmaceuticals with vitamin D₃ in order to determine appropriate storage conditions and shelf life after the product has been opened. Manufacturers rarely specify the shelf life after products have been opened, which leads to a controversial debate among medical professionals regarding the safety of products after opening and optimal storage conditions and considerably different recommendations to the public.

Methods Effect of storage conditions on the shelf life was evaluated by comparing the isothermal stability of vitamin D₃ in three prescription and three non-prescription medicines at different temperatures (4°C, 25°C and 40°C) using stability-indicating high performance liquid chromatography assay.

Results Most of the examined preparations had a higher vitamin D₃ content than the label claim when the products were first opened, presumably to compensate for loss during production and storage. An association was observed between the initial vitamin D₃ content and its stability in the preparations. The vitamin D₃ overage in liquid prescription medicines guaranteed its content >90% of the amount claimed on the label for at least 1 year when stored at 25°C and for 4 months at 40°C. All tested preparations are consumed when used as recommended over this period. Since some manufacturers recommend storage below room temperature, redefining the storage conditions is of practical significance.

Conclusions The shelf life after opening examined prescription medicines containing vitamin D₃ as their main active ingredient is at least 1 year at room temperature.