Sterilisation of the solution is not necessary, if the preparation is done properly. However, if necessary, TPGS can be sterilised without loss of effect. But, like any polyethylene glycol, already dissolved TPGS becomes less soluble on heating and might precipitate. On cooling the TPGS goes back into solution, which might take some time. Thus, for oral usage it is recommended to sterilise water and TPGS separately (if required) and to make the solution subsequently under appropriate conditions. It is sufficient, to give boiled water, which is still hot, to the weighed TPGS and to dissolve it at 40-70 °C with occasional stirring (15% solution takes up to max. 3 h). After complete dissolution, add evaporated water. A solution prepared this way (and therefore almost steril) is stable for at least 3 months and should be filled into a dropping bottle (preferably only a weekly dose) in order to keep possible contamination during application low.