The adsorption of clinically used quantities of insulin to infusion systems was studied. Isotonic saline solutions containing tracer quantities of beef insulin-I-131, with or without varying amounts of nonradioiodinated (carrier) regular beef insulin, were added to bottles of 500 ml. infusion sets. The solutions were then allowed to flow out into collection beakers. Adsorption was assessed by measuring the decrease of radioactivity in the solutions and/or recovery from the bottles by 30 per cent potassium hydroxide (KOH). The influence of human serum albumin (HSA) on adsorption was evaluated by repeating the experiments after HSA was added to the infusion fluid.

Adsorption of insulin-I-131 to both bottles and tubing was considerable, especially at low concentrations of carrier insulin. HSA effectively reduced the adsorption to clinically insignificant amounts.

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