Is Inhaled Insulin Safe for People With Asthma?

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AIR inhaled insulin versus subcutaneous insulin: pharmacokinetics, glucodynamics, and pulmonary function in asthma, by Michael Wolzt and colleagues. Diabetes Care 31:735-740, 2008

What is the problem and what is known about it so far?

In 2006, the first inhaled insulin was approved for sale in the United States. Since then, the product, called Exubera, has been removed from the market due to poor sales performance. No new inhaled insulins have emerged in the United States, although some remain in development. Inhaled insulin could remove one of the main barriers to effective insulin therapy: the need to deliver insulin beneath the skin, either through injections or via insulin pumps. Studies of inhaled insulin in diabetic patients have shown consistent safety and effectiveness, but information is limited regarding patients who have conditions such as asthma that reduce their lung function.

Why did researchers do this particular study?

The researchers wanted to find out how well one investigational inhaled insulin product, called AIR inhaled insulin, works in people with reduced lung function and those who use salbutamol, a short-acting inhaled medicine for asthma.

Who was studied?

Thirty-nine nonsmoking, nondiabetic adult subjects with or without mild or moderate persistent asthma in Vienna, Austria.

How was the study done?

Healthy, mildly asthmatic, and moderately asthmatic subjects received either AIR insulin equivalent to 12 units, 12 units of injected insulin lispro, or salbuterol plus AIR insulin (moderate asthma group only) and then underwent a glycemia clamp procedure, which allowed researchers to tell how completely the insulin was absorbed and how it acted in their bodies.

What did the researchers find?

Exposure to AIR insulin was reduced 34% in mildly asthmatic subjects and 41% in moderately asthmatic subjects compared to healthy subjects. By comparison, insulin exposure from an injection of lispro was similar in all groups. AIR insulin was rapidly absorbed in all subject groups. The effects of AIR insulin were similar in healthy and mildly asthmatic subjects but reduced in those with moderate asthma. In contrast, the effects of lispro were similar among all groups. In addition, the effects of AIR insulin were more variable in those with moderate asthma than in those with mild or no asthma. For subjects with moderate asthma, using salbuteral before AIR insulin improved both insulin exposure and effects. AIR insulin did not have any effect on lung function. Side effects including cough, headache, and dizziness were mild to moderate and already known to be associated with inhaled insulin or glycemia clamp procedures.

What were the limitations of the study?

The study involved a small number of subjects. The reduced effects of insulin in the moderate-asthma group suggest that people with moderate asthma may have some level of insulin resistance; however, the study was insufficient in design and size to draw conclusions about this possibility. Finally, the study tested how a short-acting asthma medicine might affect insulin therapy, but did not test how a long-acting asthma treatment could alter insulin treatment.

What are the implications of the study?

People who have both asthma and diabetes may be able to use AIR insulin safely, without worsening their lung function. However, the severity of their lung condition and their current treatment regimen for it can influence the effectiveness of AIR insulin in their body. It may be wise to await results of ongoing clinical trials of inhaled insulin in diabetic patients with lung disease before considering this therapeutic option.

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