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Importance of Appropriate Resuspension of NPH Before Subcutaneous Injection

Lack of resuspension alters PK/PD and result in poor glycemic controls.

NPH insulin is a two-phase solution and has to be resuspended by tipping the insulin vial or pen several times until a homogenous suspension is obtained. It has been suspected that the variability in pharmacokinetics/pharmacodynamics (PK/PD) of NPH insulin has been due to inappropriate resuspension. The authors seek out to find the differences in PK/PD of a therapeutic dose of NPH insulin (0.35 units/kg) in subjects with type 1 diabetes (T1DM) injected after appropriate resuspension compared to without resuspension.

The study was a randomized, open-label, crossover design. Subjects in the study were randomly assigned to the treatments using a Latin square, four-way, crossover design. 11 subjects were included in the study. The four different treatment groups composed of how the NPH insulin pen appears immediately before injection. In the R+ group, the NPH insulin was appropriately resuspended. However, in the R-horizontal, R-up (pen pointing up), and R-down (pen pointing down) groups, NPH insulin was injected without prior resuspension.

The primary endpoint of the study was the duration of action of the NPH regarding the different treatments. The onset of action was defined as “the time at which infusion of glucose was initiated in response to a decrease in plasma glucose concentration of 5 mg/dL below baseline.” The end of action was defined as “the time at which plasma glucose concentration consistently exceeded 118 mg/dL in the absence of glucose infusion.” The duration of action was calculated as “the difference between end and onset of action.” Additionally, the secondary endpoints were plasma insulin concentration and glucose infusion rate (GIR) (AUC0-end of study).

Results showed that duration of NPH insulin action was shorter in the R-up group (9.4 ± 1.7h) compared to the R-down group (15.4 ± 2.3h) and the R+ group (11.8 ± 2.6h) (p < 0.05). Compared to the R+ group, the R-down group has the highest AUC0-end of study than the R-up and R-horizontal group (p = 0.001). Within-subject variability among the subjects in the study was as high as 23% for PK and 62% for PD.

The authors found that when compared to appropriately resuspended NPH insulin, non-resuspended NPH insulin may result in either potentiated or reduced insulin PK/PD, depending on the position of the pen prior to injection. The R-down group, which has the injected NPH insulin being predominantly the cloudy part, rich in insulin crystals, result in greater duration of action, plasma insulin concentration, and insulin effect (GIR). With the R-up and R-horizontal groups, the predominant injected part is the clear part, therefore, very few insulin crystals are present and the PK/PD of the NPH insulin in this case is lower.

The authors concluded that lack of resuspension of NPH insulin profoundly alters PK/PD and may result in day-to-day glycemic variability and poses the patients to a risk of either hyperglycemia or hypoglycemia. More studies are warranted on the within-subject variability of properly resuspended NPH insulin compared to the other long-acting insulin on variability of PK/PD.

Practice Pearls:

  • Non-resuspension of NPH insulin associate with glycemic variability due to differences in PK/PD.
  • Appropriate resuspension of NPH insulin is needed for proper glycemic control.
  • More studies are needed to see if there are less variable in PK/PD in using long-acting insulin than NPH insulin.
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Lucidi P, Porcellati F, Andreoli AM, et al. Pharmacokinetics and Pharmacodynamics of NPH Insulin in Type 1 Diabetes Mellitus: The Importance of Appropriate Resuspension Before Subcutaneous Injection. Diabetes Care, 10 Sep 2015. Web. 21 Sep 2015.