Inhaled insulin: extending the horizons of inhalation therapy

Targeted glycemic control in patients with type 1 and type 2 diabetes is grossly inadequate, despite data demonstrating reduced microvascular and macrovascular diabetic complications with intensive treatment. A significant proportion of individuals with poorly-controlled type 2 diabetes are resistant to initiating treatment with insulin. Several decades-long search for alternative forms of insulin delivery has finally resulted in the U.S. Food and Drug Administration's approval of the first inhaled insulin delivery system, Exubera. Inhaled insulin provides hope that minimizing barriers to initiating insulin therapy will improve the overall glycemic control in both type 1 and type 2 diabetic patients. Inhaled insulin is a powder formulation that has been approved for pre-meal administration in both type 1 and type 2 diabetic patients. The delivery system for Exubera employs compressed air for producing an aerosol, which is then inhaled by the patient. Insulin is transported across the alveolar-epithelial barrier into the blood and has onset of glucose-lowering activity within 10-20 min of inhalation. The duration of action of inhaled insulin is similar to that of subcutaneous regular insulin. Although there are some limitations to the use of inhaled insulin, the potential to improve adherence and thereby achieve target glycohemoglobin levels (< or = 6.5-7.0%) in poorly controlled diabetic patients outweigh its disadvantages.