[Absorption of short-acting insulin mixed with different slow-release formulations]

Several authors point to a different action of soluble insulin when mixed with a lente formulation containing either protamine or zinc. We evaluated glucose and insulin profiles in 17 type I diabetics, every one of whom was given what was considered the optimal amount of insulin twenty minutes before a standard evening meal. The patients were studied on two occasions, one week apart. According to a randomized sequence, those who received first the protamine-soluble mixture, took the Zn-soluble combination after one week and vice-versa. At the same time, we determined anti-insulin antibodies in order to rule out any different immunological interference, in the two moments of the study. Our results confirm that protamine-insulin given together with regular shows a serum insulin peak which is earlier and higher than that obtained with the corresponding mixture of Zn-insulin and regular (ANOVA: F = 5, 96; p = 0.02); blood glucose levels were lower with the former regimen, even though the difference did not reach statistical significance. Our conclusion is that Zn-containing insulin partly inactivates regular insulin when administered in the same syringe, and this may have an impact on the long-term treatment of the diabetic patient.