Comparison of insulin levels after injection by jet stream and disposable insulin syringe

Intermediate-acting biosynthetic human (NPH) insulin was administered by disposable insulin syringe into the right upper thigh of nine insulin-dependent diabetic youths. Seven days later, the same amount and type of NPH insulin was given in the same anatomic site with a Medi-Jector II, which delivers insulin as a jet stream. Blood was collected before insulin injection and at hourly intervals subsequently for the measurement of glucose and insulin. The total serum insulin measured before the first morning dose with the needle and syringe and the Medi-Jector II was 41.2 +/- 10.7 microU/ml and 46.2 +/- 10.7 microU/ml, respectively. During the next 9 h, the areas under the respective total insulin curves were not different, but the area under the free-insulin curve after jet injection was greater than the free-insulin area after needle injection (P less than .01). The ratio of free/total serum insulin was 0.31 +/- 0.02 after needle injection and 0.40 +/- 0.03 after jet injection (P less than .0025). The peak of total insulin concentration occurred 4.2 h after jet injection of NPH: 1 h earlier than the peak after needle injection. The plasma glucose at time zero was 197 +/- 15 mg/dl before needle injection and 242 +/- 19 mg/dl before jet injection. Although the diet consumed by each subject on the 2nd study day was identical to that of the 1st day, the mean glucose increase was greater after needle-injected insulin than after jet-spray injection. This indicates that the greater amount of free insulin observed after jet-injected insulin had a direct effect in lowering the plasma glucose. Jet injection may reduce insulin requirements by increasing the availability of free insulin.