Insulin: Intestinal Absorption as Water-in-Oil-in-Water Emulsions

Abstract

PREVIOUS reports have indicated intestinal absorption of insulin in the presence of alcohol¹, saponins², quinine³ or proteolytic inhibitors^4,5. These data are often of questionable significance and are difficult to confirm. It has been generally accepted that insulin does not exhibit hypoglycaemic activity when administered orally⁶. We have investigated the possible use of water-in-oil-in-water (W/O/W) emulsions⁷ as a means of facilitating gastrointestinal absorption of normally non-absorbed water soluble biopolymers. Intraduodenal injection of such an emulsion containing insulin resulted in significant hypoglycaemic activity. These emulsions (also known as “mixed” or “multiple” emulsions) consist of oil droplets suspended in an aqueous phase, which, in turn, contain their own dispersed phase of finer water droplets. This internal aqueous phase presumably contains the therapeutic agent. Emulsions of this type are usually prepared in a stepwise manner beginning with the most finely dispersed phase. An aqueous solution of the therapeutic agent is incorporated into a continuous oil phase (using a suitable emulsifying agent). This results in a water-in-oil (W/O) emulsion which is then dispersed in a second aqueous phase (again with a suitable emulsifying agent) to give a W/O/W emulsion.