Intra-individual variability of the metabolic effect of inhaled insulin together with an absorption enhancer.

OBJECTIVE: To study the metabolic effect and the variability of the effect elicited by inhalation of 87.2 U insulin powder combined with an absorption enhancer. The metabolic effect was compared with that of 10.2 U regular insulin injected subcutaneously and of 5.5 U regular insulin given intravenously RESEARCH DESIGN AND METHODS: In this single-center open euglycemic glucose clamp study 13 healthy male volunteers received 5 insulin administrations on separate study days: once as an intravenous dose, once as a subcutaneous injection, and 3 times by inhalation, in randomized order. Glucose infusion rates (GIRs) necessary to keep blood glucose concentrations constant at 5.0 mmol/l were determined over an 8-h period after administration. RESULTS: After inhalation of the insulin powder aerosol, the onset of action was substantially more rapid than after subcutaneous insulin injection, and maximal action was reached earlier (86+/-47 vs. 182+/-53 min, P<0.0001). The maximal glucose infusion rate after inhalation of insulin was comparable to that after subcutaneous insulin injection (9.2+/-2.6 vs. 8.8+/-2.8 mg x kg(-1) x min(-1), NS). The metabolic effect in the first 2 h after inhalation was significantly greater than that after subcutaneous insulin injection (amount of glucose infused: 0.88+/-0.25 vs. 0.59+/-0.20 g x kg(-1) x 120 min(-1), P<0.0001). However, the total metabolic effect after inhalation and subcutaneous injection was comparable (2.50+/-0.76 vs. 2.56+/-0.69 g x kg(-1) x 480 min(-1), NS). The relative bioefficacy of inhaled insulin calculated in relation to the data from the subcutaneous insulin application was 12.0+/-3.5% (absolute bioefficacy 10.1+/-3.1%) but was highest in the first 2 h after application (18.5+/-3.7%; absolute bioefficacy 8.2+/-4.1%). The intraindividual variability of the metabolic response induced by insulin inhalation was 14+/-9% for the maximal glucose infusion rate, 15+/-10% for the time-to-maximal effect, and 16+/-12% for the total amount of glucose infused. CONCLUSIONS: This feasibility study shows that inhaled insulin with an absorption enhancer has a pronounced metabolic effect compared with the results of a previous study of inhaled insulin without an enhancer. The intraindividual variability of the metabolic effect was comparable with that of inhaled and subcutaneously injected insulin.