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With bated breath

The large size and fragility of therapeutic proteins mandate that most must be given via injection. While acceptable for acute indications, this route of administration is certainly not convenient for chronic diseases. Innovations have prolonged the activity of therapeutic proteins and reduced the frequency of injections, but as yet there is no delivery alternative.

Pulmonary delivery would fit the bill. With a surface area of more than 1,000 square feet, the alveolar epithelium of the lung provides an attractive target for systemic delivery, providing a large area for drug deposition and absorption. However, the difficulty of delivering liquid or powder through the upper airways, and the inefficiencies of compound transport, still can be a formidable challenge. In addition, the quick rate of absorption though the lung may preclude the use of the inhaled platform for drugs that need to be released slowly.

Finally, because the main benefit of treatment is convenience, the regulatory authorities are focused on safety, making the regulatory path longer, if perhaps not more difficult, than that of conventional treatment.

Pulmonary portents

Pulmonary drug delivery has long been used to deliver small molecules to patients suffering from maladies of the lung and has more recently been used to deliver Pulmozyme recombinant DNase I, marketed by Genentech Inc. (DNA, South San Francisco, Calif.) to treat cystic fibrosis. But no company has yet succeeded in gaining regulatory approval to systemically deliver a protein therapeutic through an inhaled mechanism.

However, there are at least eight products in the clinic covering five different proteins.And a look at the number of proteins that are marketed for chronic indications suggests there is ample room for growth in this field (see "Inhaled Protein Pipeline," A2 & "Chronic Biologics," A3).

To be successful, companies pursuing the inhaled route must be able to show that it is as effective as its injected counterpart. Early returns from clinical trials of inhaled insulin, which is furthest along in clinical development, show promise.

Exubera, an inhaled insulin from partners Inhale Therapeutic Systems Inc., Pfizer Inc.

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