November 2002 / Volume 47 / Number 11 / Page 1256
Liquid Nebulization: Emerging Technologies
Delivery of aerosolized medications into the lungs is becoming increasingly important for two reasons. First, medications aimed at lung diseases often have a higher therapeutic index when delivered directly into the lung. Although bronchodilators are currently the most common aerosolized medication, many new classes of drugs (eg, antibiotics, antioxidants, and anti-inflammatory agents) are being developed that lend themselves to this mode of delivery. Second, medications aimed at systemic illnesses (eg, insulin, human growth factor, and calcitonin) are also being administered as aerosols and are being shown to have reliable systemic delivery through alveolar-capillary transport.
Current aerosol delivery systems may not be adequate for these new applications. This is because current systems can be very inefficient, and aerosol delivery can be heavily dependent on a variety of sometimes difficult-to-control factors, including breathing pattern, airway geometry, humidity, aerosol particle size/shape/velocity, and device performance characteristics. Under optimal conditions lung deposition may approach 50% with these systems. Unfortunately, however, all too often in clinical practice, lung deposition is considerably less than that, especially in pediatric patients and uncooperative adults. Efficient delivery can be further compromised by the presence of an artificial airway. Though these inefficiencies are clinically manageable for inexpensive drugs such as bronchodilators (just give more drug), they are unacceptable when considering aerosol delivery of potentially very expensive newer medications.
An additional problem in current aerosol delivery is specific location targeting. Many drugs are more effective if they are placed in specific regions within the lung. For example, drugs designed for parenchymal diseases might be most effective if delivered to alveolar regions. Conversely, drugs designed for airway disease might be most effective if delivered to proximal airways. Though some targeting can be accomplished by particle size and velocity manipulations (smaller, slower particles deposit more distally), current technology has limited targeting capabilities.
Some fascinating new approaches to aerosol delivery are on the horizon. These include novel device characteristics, new drug formulations, clever patient interfaces, and approaches that generate the aerosol within specific regions of the lung. The purpose of the 30th RESPIRATORY CARE Journal Conference was to gather recognized experts in nebulization and aerosol delivery and address these developments in several ways. The program was structured in 3 parts: (1) a review of basic nebulization principles and limitations of current systems, (2) discussions about how assessments of future systems should be done and what would be the barriers to implementation, and (3) specific analyses of the concepts underlying new devices and interfaces.
This and the next issue of RESPIRATORY CARE provide the proceedings of the conference on Liquid Nebulization: Emerging Technologies. We hope that these articles will increase understanding of aerosol delivery and provide insight as to how newer design principles can improve upon this very useful form of drug delivery.
Myrna B Dolovich PEng
Departments of Medicine and Nuclear Medicine
Neil R MacIntyre MD FAARC
Respiratory Care Services
Duke University Medical Center
Durham, North Carolina
Gerald C Smaldone MD PhD
Pulmonary/Critical Care Division
Department of Medicine
State University of New York at Stony Brook
Stony Brook, New York