Aims: To evaluate the completeness of insulin resuspension by users of neutral Hagedorn (NPH) insulin pens and premixed insulin pens and to relate this to how patients mix insulin before injecting.
Methods: Patients (n = 180) administering a medium duration or premixed insulin in cartridges in disposable pens were asked questions about mixing insulin, injection technique and storing insulin. They were also asked to demonstrate how they mixed their insulin and to send in a half-used pen. The cloudy component equates to the complexed insulin, while the clear component is the diluting fluid or soluble insulin, depending on the type of insulin used. The optical density, a simple way of measuring cloudiness, was measured in each cartridge or disposable pen and was compared with the range obtained from a series of unused control pens. The results for 146 pens containing the most commonly used insulin were included. The 21 patients whose residual pen insulins showed optical densities > 5 SD from the mean were re-interviewed and their medical records were examined in detail. Insulin in the pens was also measured by immunoassay to confirm the utility of optical density measurements.
Results: Only one patient mixed the insulin as the manufacturers recommended. In 58 out of 146 pens or cartridges (40%) the opacity of the insulin varied significantly from the expected value.
Conclusions: Most patients in Kirkcaldy do not mix insulin adequately. This may result in their giving different incorrect doses of insulin during the use of each pen. More emphasis should be given to teaching patients to mix correctly.