In vitro release of insulin aspart incorporated into water-in-oil emulsions

Release of therapeutically active proteins in sufficient and controllable amounts is essential in the formulation of new drug delivery systems containing protein. The release of the insulin analogue, insulin aspart, from water-in-oil emulsion is modified by varying the amount of internal aqueous phase and by varying the osmotic gradient. The increase in the osmotic gradient from 135 to 171 mOsm kg(-1) between the internal aqueous phase and the release media increased the amount released from approximately 0.4 to 28% after 24 h, whereas the variation in the internal aqueous phase from 60 to 40 w/w% water in the present experiment did not have any measurable effect on the amount released. The incorporated insulin aspart only exhibits minor secondary structural changes, when incorporated into the emulsion. Thus, the present water-in-oil emulsion may be a possible candidate as a drug delivery system for proteins.