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The field of inhaled pharmaceutical aerosols is growing rapidly. Various indicators suggest this field will only expand more quickly in the future as inhaled medications for treatment of systemic illnesses gain popularity. Indeed, worldwide sales of inhalers for treating respiratory diseases alone are expected to nearly double to $22 billion by 2005 from the estimated 1997 value of $11.6 billion. However, this is only the start of what is likely to be a much larger period of growth that will occur because of the increasingrealization that inhaled aerosols are ideally suited to delivery of drugs to the blood through the lung. Indeed, in the future, inhaled aerosols are expected to be used for vaccinations, pain management and systemic treatment of illnesses that are currently treated by other methods.
With the explosive growth of inhaled pharmaceutical aerosols comes the need for engineers and scientists to perform the research, development and manufacturing of these products. However, this field is interdisciplinary, requiring knowledge in a diverse range of subjects including aerosol mechanics, fluid mechanics, transport phenomena, interfacial science, pharmaceutics, physical chemistry, respiratory physiology and anatomy, as well as pulmonology. As a result, it is difficult for newcomers (and even experienced practitioners) to acquire and maintain the knowledge necessary to this field.
The present text is an attempt to partially address this fact, presenting an in-depth treatment of the diverse aspects of inhaled pharmaceutical aerosols, focusing on the relevant mechanics and physics involved in the hope that this will allow others to more readily improve the treatment of diseases with inhaled aerosols.
Chapter 1 supplies a brief introduction for those unfamiliar with the clinical aspects of this field. Chapter 2 is a short introduction to particle size concepts, which is important and useful to those new to the field, but which is standard in aerosol mechanics. Chapter 3 lays down the basic equations and concepts associated with the motion of aerosol particles through air, including the effects of electrical charge. The complications added by considering particles that may evaporate or condense, as commonly occurs with liquid droplets in nebulizers and metered dose inhalers, are dealt with in detail in Chapter 4.
Chapter 5 introduces some basic aspects of breathing and respiratory tract anatomy, while Chapter 6 introduces the concepts of fluid motion in the respiratory tract. Both chapters are necessary for understanding subsequent chapters, particularly Chapter 7 which delves deep into the details of aerosol particle deposition in the respiratory tract, one of the most important aspects of inhaled pharmaceutical aerosols.
The last three chapters of the book each introduce basic aspects of the mechanics of the three major device types currently on the market: nebulizers, dry powder inhalers, and metered dose inhalers. From a traditional engineering point of view the mechanics of these devices has not been well studied, so that a reasonable part of this material is speculative, drawing on work done in related engineering applications and extrapolating in an attempt to gain some understanding of the mechanics of existing aerosol delivery devices.
Any book will have its shortcomings, and the present one is no exception. In particular, there are several topics that I would have liked to include, but have chosen not to because of time and energy limitations. Some of these neglected topics include nasal administration of aerosols, the mechanics of several new and promising delivery devices (including various novel powder and liquid systems about to be launched on the market), various aspects of formulation, as well as particle sizing methods. My apologies to those who had hoped for coverage of these topics. However, this book has taken far longer to complete than I had planned, and the time has come to send it to the presses.
W. H. F.
Edmonton
September 2000
