It is hard to believe that in ten short years since the publication of Pharmaceutical Inhalation Aerosol Technology the number of chapters would be increased two-thirds in order to bring the second edition up to date. But it is true! For one who had the privilege of experiencing the heady days, nearly a half century ago, during the development of early metered-dose inhalers (MDIs), the accelerated pace of development in inhalation technology during the past decade has been truly astonishing.

In the early days, we didn't have the foggiest idea of how much of the drug discharged from our MDIs actually deposited in the lung: we only knew that those patients were getting relief for their asthma. Today, using recently developed mathematical models that are based on lung morphology and aerosol physics, we can estimate with reasonable certainty the amount of drug delivered from an inhaler that is expected to be deposited in the lung. New methods of imaging appropriately labeled drug discharged from inhalers provide exquisite pictures of the distribution and accurate estimate of the quantity of drug deposited in the lung. Greater understanding of the cell biology of the lung and of the pharmacodynamics and pharmacokinetics of drug in the lung helps us understand what happens, and the rate at which it happens, to drug deposited there.

Methods of aerosol generation—ultrasound, electrohydrodynamics, hydrostatic pressure extrusion of liquid through small orifices—that, just ten years ago, might have been considered laboratory curiosities or perhaps only implemented as laboratory prototype generators, are now in late-stage development as handheld inhalers. In addition, precision dry-powder inhalers are in late-stage development. Chlorofluorocarbon (CFC)-free MDIs, often more efficient than their CFC counterparts, are on the market. The dream of delivering insulin by inhalation to eliminate injection in the treatment of diabetes is coming to fruition. Inhaled insulin, delivered by precision dry-powder inhalers and from metered aqueous-aerosol inhalers, is in late-stage clinical trials with very encouraging results. Ten years ago, gene implantation from inhaled aerosol was only beginning to be talked about. Today it is being explored in clinical trials as treatment for cystic fibrosis. Proteins and peptides comprise a growing number of drugs coming from the biotech industry that are now being developed as aerosol dosage forms.

Keeping pace with this technological development, the science and understanding of formulation factors that govern aerosol generation, of factors governing pulmonary deposition, and of the chemical and biological fate of drug deposited in the respiratory tract are burgeoning. For one experienced in the development of pharmaceutical aerosols, this second addition of Pharmaceutical Inhalation Aerosol Technology provides, in a compact way, a useful overview of new developments in the technology. This volume will be particularly useful for the many people entering this increasingly exciting field—pharmaceutical scientists, engineers, and clinicians. It will provide them with a jump start to bring them up to speed in this rapidly expanding field.

Charles G. Thiel

3M Drug Delivery Systems Division, Retired

Maplewood, Minnesota, U.S.A.

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