Enhanced vaginal absorption of insulin in sheep using lysophosphatidylcholine and a bioadhesive microsphere delivery system

Abstract Insulin was administered vaginally to sheep as an aqueous solution and as a lyophilised powder with bioadhesive starch microspheres. The effect of lysophosphatidylcholine (LPC) on the vaginal absorption of insulin from both formulations was studied. While the vaginal absorption of insulin from insulin solution was minimal, the addition of LPC resulted in a rapid rise in plasma insulin and a pronounced fall in plasma glucose levels. The absolute bioavailability of the peptide from the latter solution was 13%. The hypoglycaemic response to vaginally administered insulin was also improved using the microsphere delivery system, compared to insulin solution alone, and was further enhanced by LPC. Vaginal absorption of insulin from each formulation appeared to be influenced by the oestrous cycle and was thought to correlate with changes in vaginal histology.