This study describes the pharmacokinetics of three intermediate-acting insulin preparations, NPH porcine insulin, NPH human insulin (recombinant DNA), and “Depot-A” insulin, a mixture of 20% regular and 80% NPH human insulin from Eli Lilly and Company. Metabolic healthy normal weight volunteers were selected for the study. After overnight fasting, each test person received 0.4 U of each insulin per kg body weight injected subcutaneously in the triceps area of the arm. To prevent severe hypoglycemia, the test persons were connected to a “GCIIS Biostator” with blood glucose clamp at the 60 mg/dl level. Peripheral blood was sampled at regular intervals for glucose, insulin, and C-peptide determination. More elevated insulin levels were measured after application of both NPH human insulin and “Depot-A” insulin than after NPH porcine insulin. A more rapid decrease in the blood glucose concentration was observed after injection of both human insulin preparations than after porcine insulin. The dextrose output of the “GCIIS Biostator” was more pronounced in both human insulins than after the porcine preparation. After the injection of NPH human and NPH porcine insulin, significant differences were calculated between the concentrations of these two insulins in the blood, from the 2nd to the 10th hour (P < 0.05-P < 0.005) and between the dextrose output of the “GCIIS Biostator” from the 3rd to the 8.5th hour (P < 0.05). The fall of the C-peptide concentration to the lower detection limit of the assay reflects suppression of the endogenous B-cell secretion and confirms the measure of peripheral insulin concentrations as a result of the exogenously applied insulin. Although all investigations were performed under identical experimental conditions and equal dosages of each insulin were injected, higher insulin concentrations and a stronger biologic effect, shown by larger amount of dextrose delivered, were observed in both human insulins than in porcine insulin. Why this phenomenon occurs is as yet unclear. The clamp technique used with the “GCIIS Biostator” enables establishment of the biologic profile of any insulin, and thus represents a valuable tool in comparative studies.

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