Determinants of insulin availability in parenteral nutrition solutions.

Background: Management of hyperglycemia in patients receiving parenteral nutrition (PN) often includes the addition of regular insulin to the PN solution. A literature review has shown insulin availability in such solutions to range from 10% to 95%. This discrepancy in availability may be due to differences in the composition of the PN solution, the final concentration of insulin, or the assay method used to determine insulin concentrations. The purpose of this study was to evaluate insulin recovery from a standard PN solution used at our medical center.
Methods: Solutions were manually prepared in our pharmacy according to standard practice. Multivitamins and trace elements were added to 1 of 2 L of solution each day. Each of 3 simulated patients received 2 L of solution per day for 3 consecutive days. Samples from each bottle were drawn at baseline, 1 hour after the start of infusion, and 1 hour before the end of infusion and were subsequently analyzed for immunoreactive insulin levels by radioimmunoassay.
Results: Recovery of insulin from solutions containing multivitamins and trace elements was much greater (95%) than from those without (5%).
Conclusions: The presence of multivitamins and trace elements is a major determinant of insulin availability in PN solutions. Additional research is necessary to determine the mechanism mediating this effect and to assess its clinical significance.