Effects of absorption promoters on insulin absorption through colon-targeted delivery

The aim of this study were to investigate the effect of sodium glycocholate (GC-Na) as an absorption promoter and the effects of the co-administration of GC-Na and various absorption promoters on orally administered insulin absorption utilizing a colon-targeted delivery system. The system containing insulin and GC-Na (CDS) was administered to dogs, and plasma glucose and insulin levels were then measured at 24h after administration. For CDS, the C(max) in plasma glucose level was significantly higher than a reference formulation without GC-Na. The pharmacological availability for CDS was not significantly higher than the reference formulation. In contrast, CDS with poly(ethylene oxide) as a gelling agent (CDSP) showed prolonged hypoglycemia effects. The pharmacological availability was 5.5% and significantly different from the reference formulation. The absolute bioavailability for CDS was 0.25%, and for CDSP it was 0.42%. Consequently, the results of this study demonstrated that colon-specific delivery of insulin with GC-Na was more effective in increasing hypoglycemic effects after oral administration, and the combination of GC-Na and poly(ethylene oxide) tended to prolong the colonic absorption of insulin and might be more effective for improvement of orally administered insulin absorption utilizing the colon-targeted delivery system.