Determination of the binding constant between alprostadil and alpha-cyclodextrin by capillary electrophoresis: implications for a freeze-dried formulation.

The binding constant between alprostadil (PGE1) and alpha-cyclodextrin (alpha-CD) was determined at three temperatures by capillary electrophoresis. alpha-CD is an excipient material in Caverject Dual Chamber Syringe (DCS), added to enhance stability. The binding constant was used to calculate the amount of PGE1 free upon reconstitution and injection, the latter of which is critical to product performance.