Sorption of unoprostone isopropyl to packaging materials.

This study investigated the stability of an ophthalmic solution formulation of unoprostone isopropyl (UI), a prostaglandin like compound, in two types of packaging materials, polypropylene (PP) and low-density polyethylene (LDPE). We determined the concentration of UI and its degradation products as a function of time and found that the rate of disappearance of drug was faster for the formulation stored in LDPE bottles than that stored in PP bottles. Further studies indicated that the inferior stability observed with the LDPE packaging was primarily due to the sorption of UI to the packaging material and to a lesser degree, chemical degradation. The sorption was temperature dependent, lowering the temperature reduced the sorption, thus improving the shelf-life of the product.