Intrapulmonary administration of insulin to healthy volunteers

Objectives. To study the biological effects of nebulized insulin, administered intrapulmonary, to healthy volunteers.
Design. A double-blind, randomized, controlled intervention study.
Setting. The department of Internal Medicine, University Hospital, Linköping, Sweden.
Subjects. Eight healthy, non-smoking volunteers, with a mean age of 28 (range 22 to 56) years.
Interventions. Regular human insulin 100 U mL^-1 (Actrapid®) or 0.9% saline was given randomly as an oral inhalation. Insulin was given in three different doses (40, 80 and 160 U). Aerosol was generated by a new jet nebulizer.
Main outcome measures. Blood glucose, serum insulin, and serum C-peptide.
Results. After the 160 U insulin dose the blood glucose concentration (mean±SE) fell from 4.3±0.2 to 2.8±0.2 mmol L^-1 ( P <0.001), concomitant with an increase in mean serum insulin concentrations, rising from 9.5±1.5 to 26.1±2.5 mU L^-1 ( P <0.001). Serum C-peptide concentrations simultaneously decreased from 0.48±0.03 to 0.12±0.02 mmol L^-1 ( P <0.001). All changes were dose dependent. No adverse reactions were noted and no significant changes in lung function tests.
Conclusions. Intrapulmonary insulin administration to healthy subjects can induce a significant hypoglycaemia and cause a clinically relevant increase in serum insulin concentrations. If similar results can be obtained when administering insulin to diabetic subjects, this insulin administration route can be a future complement to certain groups of patients.