Assessment of gelling in insulin solutions for infusion pumps

Prolonged, gentle agitation of U100 insulin solutions containing various ingredients has shown that gelling can take place. The extent of gelling was evaluated by low shear rheometry and quantified in terms of the effective molecular weight increase using the method of reduced variables. Maximal viscosities of gelled systems in excess of 100 Pas were achieved. From a knowledge of the hydrodynamics of infusion pump systems, the reduction in insulin delivery rate caused by an increase in viscosity can be calculated. In commercial, syringe-driven pumps, pressure differentials as high as 10(4) Nm-2 and shear rates in excess of 10(4) s-1 can occur, although the flow is invariably laminar.