IMPROVED GLYCEROL/INSULIN FORMULATION FOR USE IN IMPLANTABLE PUMPS.

The success of glycerol in preventing occlusion is evident in that the average functional lifetime (elapsed time from date of implantation to date of explanation) of an implanted insulin pump now exceeds 3 years. During clinical trials with glycerol/insulin it soon became clear that although these formulations did not clog the infusion pumps they tended to lose bioactivity, necessitating an interval of 10 to 14 days between refills. Further study indicated that glycerol impurity might be an important factor underlying insulin instability. Thus, the authors replaced United State Pharmacopeia (USP) rendered glycerol with USP spectrographic grade synthetic glycerol. The glycerol was further purified, then glycerol/insulin samples were incubated at a range of pH values to determine the effect of pH on chemical stability. A comparison of characteristics of the previous and current insulin/glycerol formulations is presented. Study methods and results are discussed.