[Adsorption of insulin directly added to infusion bottles]

A study of insulin adsorption to infusion system was undertaken in the situation of direct addition of insulin alone in the infusion bottles, with use of 125I-labelled insulin and non labelled insulin. The infusion solutions tested were glucose solutions (5, 10, 15 and 30%). There is an important adsorption of insulin (75%) to the infusion system when the insulin concentration in the solution is low. The effluent insulin is not degraded. The glucose content of the solution does not influence the phenomenon. Adsorption of insulin decreases when the insulin concentration in the solution is increased and a plateau is reached starting from an insulin concentration in the solution of about 400 ng/ml; at higher concentrations, 80 to 90% of insulin that has been initially put in the bottle is recovered. Since the insulin concentrations in the solutions used in clinical practice are higher than 400 ng/ml, this adsorption phenomenon can be neglected and therefore can explain the efficiency of this mode of insulin-therapy. Kinetics of effluent insulin is a plateau, stable all along the infusion. Thus, direct addition of insulin alone into infusion bottles is an efficient and controlled mode of insulin-therapy if a minimal insulin concentration in the infused solution has been reached.