A comparison of the pharmacokinetics of human protamine sodium insulin with human isophane insulin following subcutaneous injection in normal subjects.

The pharmacokinetics of human protamine sodium insulin 0.6 mg% were compared with those of human isophane zinc insulin using the glucose clamp technique. The insulin preparations were administered subcutaneously at a dose of 0.5 U/kg in 7 normal subjects; a placebo injection served as control. Plasma insulin and C-peptide concentrations were then measured over 24 hours. After correction of the results to allow for endogenous insulin secretion the two insulin preparations gave similar values throughout the study except that protamine sodium insulin achieved an earlier peak in plasma insulin concentration (90 minutes) compared to isophane (120 minutes). When measured by an index of the dextrose infusion rate required to maintain euglycaemia the two insulin preparations gave similar values for the first 16 hours, maximum values being obtained during the fourth hour after administration. Using this index isophane zinc insulin gave higher values during the 17th, 19th and 21st hours following administration suggesting it may have a slightly more prolonged action than protamine sodium insulin.