Review: Current status of the development of inhaled insulin

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Abstract
The most promising alternative route of insulin administration seems to be pulmonary delivery by inhalation. For a maximal rate of absorption insulin must be applied deep into the lung, i.e., into the alveoli. A number of inhalers designed to generate an aerosol with an appropriate particle size for pulmonary delivery are currently in clinical development. The pharmacodynamic effects of insulin formulations administered via the lung are comparable to, or are even faster than, those of subcutaneously injected regular insulin or rapid-acting insulin analogues. The relative biopotency of inhaled insulin is approximately 10%, i.e., the dose of inhaled insulin must be 10 times higher than the dose applied subcutaneously in order to induce a comparable metabolic effect. Clinical trials indicate that metabolic control with this pain free route of insulin administration is at least comparable to that of subcutaneous (sc) insulin therapy. Side effects. observed in human trials, gave rise to safety concerns that have delayed development for several years. Nevertheless, recent long-term safety studies indicate that the increased stimulation of insulin antibody formation stopped after some time and that the observed changes in lung function were minor or reversible. Consequently the first application for an approval of pulmonary insulin has been submitted to the authorities. In summary, it seems as if, after several decades of research, for the first time a feasible alternative route for insulin administration is within Reach.