Hypoglycemic effect of oral insulin in diabetic rabbits using pH-dependent coated capsules containing sodium salicylate without and with sodium cholate

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The hypoglycemic effect of oral insulin (20 U and 40 U) capsules coated with a pH-dependent soluble polymer (Eudragit S100) and containing sodium salicylate (50 mg) without and with sodium cholate (50 mg) was studied in alloxan-hyperglycemic rabbits and compared with that of s.c. insulin injection (20 U). The capsules containing 20 U insulin + sodium salicylate (50 mg) produced a significant reduction in plasma glucose level to 82 and 73% of initial values at 2 and 3 hr after administration, respectively. The blood glucose level slowly returned to normal values at 5 hr. The AUC(0-5 hr) was 73.7 ± 43.5 mg · hr/dl compared to 242 ± 70.5 mg · hr/dl for insulin (20 U, s.c.) with a relative hypoglycemia of 30.4%. A higher dose of oral insulin (40 U) ± sodium salicylate (50 mg) was more effective in reducing plasma glucose level which steadily decreased and reached 56% of the initial value by 5 hr (AUC(0-5 hr) = 132 ± 41.5 mg · hr/dl and relative hypoglycemia = 27.3%). Sodium cholate (50 mg), however, slightly improved sodium salicylate effect producing an AUC(0-5 hr) of 139 ± 37.3 mg · hr/dl with relative hypoglycemia of 28.7%. The relative hypoglycemia of pH-dependent coated capsules reached in the present experiment is the highest found so far.

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