Influence of concentration on the kinetics of SC-infused insulin. Comparison between square-wave SC infusion and bolus SC injection.

The influence of various concentrations of a constantly SC-infused insulin solution on plasma free insulin (PFI) levels wa studied in eight type 1 diabetic subjects. Soluble insulin at three different concentrations (10, 40, and 100 U/mL) was pumped at two different rates: 1.5 U/h between meals and 15 U/h for 30 minutes just before meals. For each randomly allocated concentration, PFI levels were studied twice in the same day during two six hour postmeal periods. In addition, at the end of the U40 infusion, a comparable amount of insulin was injected as a bolus. The total amount (56 U/d) and distribution of insulin delivered were similar in all patients and with each concentration. The mean maximum PFI levels were 39 +/- 7.2, 28.4 +/- 3.4, 36.2 +/- 6.4, and 29.2 +/- 7.6 mus U/mL, respectively, during the U10, U40, and U100 infusions and the U40 bolus injection; these values were observed, respectively, 60, 120, 90, and 90 minutes after a step up increase of insulin infusion and after the SC bolus injection. PFI levels returned to basal values between three and five hours after the step decrease. There was no significant difference in the kinetics of PFI levels variation, whatever the concentration in the range of 10 to 100 U/mL. For U40 these kinetics did not differ from that observed after a bolus SC injection of soluble insulin.