Several pharmaceutical companies have developed inhaled insulin, and exubera from Sanofi aventis and Pfizer has been approved in several countries.
The lungs with their large surface area and the thin alveolar epithelium allow rapid absorption of inhaled insulin . The bioavailability has a range of 15-25% . The exubera insulin is a fine powder insulin in doses of 1 or 3 mg, corresponding to approximately 3 and 9 units of human insulin. The clinical trials have shown that the insulin antibody levels increase with the use of inhaled insulin, but this has not been linked to any changes in glycemic control and episodes of hypoglycaemia or allergic reactions . The pharmacokinetic profile of exubera is quite similar to that of rapid-acting insulin analogues, but with a duration of action between that of rapid-acting analogues and fast-acting human insulin .
The development of inhaled insulin must be seen in the light of a substantial resistance to insulin therapy in patients with type 2 diabetes and physicians who care for the patients. The reasons for this resistance include anticipated pain, inconvenience, fear of hypoglycaemia and weight gain [55,56].
Several clinical controlled trials have evaluated treatment with inhaled insulin. In 779 type 2 patients with an HbA1c >8% the availability of inhaled insulin as a treatment option significantly increased the proportion of patients who would theoretically choose insulin treatment . Thus, patients were three times more likely to choose insulin when inhaled insulin was available compared with conventional insulin treatment .
In the first smaller randomised trial 68 type 2 patients with HbA1c between 8.1 and 11.9% despite treatment with sulfonylurea and/or met-formin were randomised to receive inhaled insulin in addition to pre-study OHA (oral hypoglycaemic agents) or to continue to take OHA alone for 12 weeks . After 12 weeks a mean reduction in HbA1c of 2.3% was found in the first group, compared with 0.1% in the group treated with OHA alone . No long-acting insulin was used in the study.
In another study exubera was used in monother-apy or added to dual oral agent therapy in type 2 patients with an HbA1c between 8% and 11% . The study design was a 12-week open label randomised trial. Exubera was used as a premeal insulin in the two insulin arms with either dual oral agents or as monotherapy. In the third treatment arm patients continued receiving dual oral agents . At week 12 both inhaled insulin groups had a significantly greater reduction in HbA1c of 1.9% and 1.4%, respectively . In the control group the decrease in HbA1c was 0.2%. Hypoglycaemia and cough were more often reported in the two groups treated with inhaled insulin. Pulmonary function tests showed no statistically significant differences between the groups, but increased insulin antibody titers were observed in the inhaled insulin groups .
In a 6-month study type 2 diabetic patients were randomised to treatment with premeal inhaled insulin plus bedtime ultralente or at least two injections of subcutaneous insulin (premix human/NPH insulin) . HbA1c decreased similarly in both groups (0.7% vs. 0.6%), and no difference was found in the number of hypoglycaemic events. Insulin-binding antibodies increased more in the inhaled insulin group .
In the study by DeFronzo and coworkers, inhaled insulin was compared with rosiglitazone in 150 patients with suboptimal control on diet and exercise (HbA1c 9.4%) . The HbA1c reduction was greater in the inhaled insulin group (2.3%) compared with 1.4% in the rosiglitazone group.
Lastly, Barnett et al. in a 24-week study randomised type 2 patients uncontrolled on sulfony-lurea monotherapy to inhaled insulin before meals or metformin and demonstrated in subjects with HbA1c >9.5% at randomisation a greater reduction in HbA1c in the inhaled insulin-treated group (2.2% vs. 1.8%) . In the patients with HbA1c <9.5% at randomisation, the decrease in HbA1c was not different between the two groups. More events of hypoglycaemia were observed in the inhaled insulin group .
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