Interaction between plastic catheter tubings and regular insulin preparations used for continuous subcutaneous insulin-infusion therapy.

In search of possible interactions between plastic tubings used for insulin-pump treatment and commercial regular insulin preparations, various catheter sets made from polyvinyl chloride (PVC), polyethylene (PE), and nylon plastics were perfused at 30 degrees C in a laboratory setting for up to 72 h. The perfused insulin solutions were analyzed by high-performance liquid chromatography and atomic absorption spectroscopy. Although no plasticizer, e.g., dioctyl phthalate, or nickel or chromium ions were found in the perfusates, substantial interactions between the plastics and the insulin solutions were detected, extraction of bacteriostatic additives from the insulin solutions in particular. The PVC retained up to 88% of the bacteriostatics from the insulin preparations, whereas PE tubings retained only 10-15%. Whether the loss of preservatives during perfusion through PVC catheters predisposes to cutaneous infections during insulin-pump therapy remains to be shown.