In January 2006 the US Food and Drug Administration approved the first inhalable insulin preparation for treatment of types 1 and 2 diabetes mellitus. This preparation, marketed by Pfizer, is a dry, powdered, human, regular insulin that is made into an aerosol mechanically by a handheld device at the time of inhalation. The powder is prepackaged in 1 mg foil packets that deliver 3 units of insulin and 3 mg packets that deliver 9 units. Because one unit of subcutaneous insulin corresponds to about 30 μg insulin, the activity of inhaled insulin is only about 10% of injected insulin on a weight basis.

This “inefficiency” in comparison to subcutaneous insulin brings up the reproducibility of dosing. Firstly, in clinical trials the overall incidence of hypoglycaemia seems comparable with inhaled and subcutaneous insulin when comparable levels of glycaemic control are obtained. However, severe hypoglycaemia was more common and mild hypoglycaemia less common with the inhaled product in some trials. This will bear watching in longer term follow-up studies. Secondly, pulmonary factors (specifically smoking status and asthma) affect the absorption of inhaled insulin, with increased absorption in smokers and decreased absorption with asthma. Therefore, populations in whom the variability of absorption is greatest …