Influence of absorption promoters on pulmonary insulin bioactivity

The purpose of this research was to enhance the bioactivity of insulin by the pulmonary route using a combination of absorption promoters. Aliquots (100 microL) containing 1.0 IU/kg to 7.0 IU/kg doses of porcine insulin solutions with different classes of absorption promoters and combinations of these at 3 concentration levels were instilled intratracheally to the anesthetized rats. Blood concentrations of glucose were measured at specific time points. Out of 3 concentration levels of each of the absorption promoters used, the formulations having the least concentration with the maximum percentage of blood glucose reduction were selected for combining absorption promoters, and their pharmacodynamic parameters related to insulin absorption were determined. The pharmacodynamics of porcine insulin following subcutaneous administration of increasing doses were also determined. The relative pulmonary bioactivity of insulin in phosphate buffer pH 7.4 and citrate buffer pH 3.5 was 11.36% +/- 1.27% and 43.20% +/- 2.48%, respectively, compared to subcutaneous administration. Relative pulmonary bioactivity of 155.60% +/- 5.19% was obtained when oleic acid sodium salt, sodium tauroglycocholate, bestatin, and chymostatin were coadministered in citrate buffer pH 3.5 solution. However, only 61.91% +/- 3.21, 67.09% +/- 3.23%, 67.24% +/- 2.11%, and 69.84% +/- 3.02% were obtained, respectively, upon incorporation of these absorption promoters individually. Absorption promoters in combination have significant potential for increasing the pulmonary bioactivity of insulin. These studies support the argument that pulmonary administration of insulin is a viable alternative to subcutaneous administration for diabetic patients.