Influence of temperature and time on insulin adsorption to plastic bags

The influence of temperature and time on insulin adsorption to plastic peritoneal dialysis bags was evaluated. A dialysis bag (1.5% dextrose, 2 liters) was injected with 25-microCi insulin I 125 and gently mixed. This bag was then attached to another empty bag of the same type. Following a bag-to-bag transfer method, the amount of insulin adsorbed on the plastic bags was measured at 24 degrees C and 37 degrees C, and after a 12-hour warming period at 37 degrees C. Regular insulin was added to the system in 40-unit increments up to 280 units. Radioactivity in all of the samples was measured in a gamma counter. As the amount of regular insulin increased, the percentage of insulin adsorbed decreased at both temperatures. More insulin was bound at 37 degrees C than at 24 degrees C for all levels of insulin. Data calculated according to the Langmuir isotherm equation showed that the maximum possible values of adsorption to the system at 24 degrees C and 37 degrees C were 17.8 and 18.4 units, respectively. The affinity constants at 24 degrees C and 37 degrees C were 0.0039 and 0.0065, respectively. The influence of prolonged warming at 37 degrees C was minimal. At the usual dosage of insulin (below 40 units) prescribed to the majority of dialysis patients, less than 9% (3.5 units) is adsorbed onto the dialysis bags.