Insulin wastage using a fixed mix of insulin with a pen The practice of patients in one clinic

People with diabetes who administer a premixed insulin with a pen may require a largedose. Pens contain 150 or 300 units of insulin which is unlikely to be an exact multiple of the dose. Patients were asked what they did when the reservoir approached exhaustion. Twenty seven out of 110 patients were regularly giving two injections of insulin to avoid waste, although none had been instructed to do so. Seven other patients were taking action to avoid waste including five who were giving the wrong dose. The wastage of insulin is much less when using a 3 ml disposable pen than when using a 1.5 ml cartridge. If patients are instructed to use pens containing 300 units and advised to use the insulin left at the end of a pen for the smaller injection, the amount of insulin wasted is 3.6% compared with 13.6% wasted when using 1.5 ml cartridges. The total cost of insulin when using a dis‐posable pen is approximately one and a half times more than when using a cartridge, twice as much as when using a vial of the same human insulin, and two and half times more than when using pork insulin.