CIMIT Summer Education Series 2009: Frontiers of Inhalation Technologies in Biomedical Sciences and Clinical Medicine

7.7.2009 Inhalation Technology Fundamentals: Design Factors Influencing Aerosol Delivery by Pharmaceutical Inhalers SPEAKER: Anthony J. Hickey, PhD, DSc: University of North Carolina MODERATOR: Jose Venegas, PHD: HMS, MGH

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Forum Summary

The size of an inhaled particle largely determines where in the lungs it will deposit.  Particles more than five microns in diameter almost always experience inertial impaction in the mouth and throat, where the air velocity is high and directional change is significant.  Particles between one and five microns in diameter usually sediment in the trachea and bronchi, where the air velocity is lower and directional change is not so extreme.  Particles less than one micron in diameter usually deposit in the alveoli, where the air velocity is so slow.  Most inhalers and nebulizers are designed to produce particles between one and five microns in diameter.

Aerosol delivery systems can be divided into three major categories.  The metered-dose inhaler consists of a canister containing pressurized propellant, a metering chamber, and a valve.  These inhalers are usually used to deliver less than 5 milligrams of a given drug.  The dry-powder inhaler consists of a dry powder, a metering system, and an aerosolization system.  These inhalers can deliver up to ten milligrams of a given drug.  Finally, the nebulizer consists of a liquid and an air source that aerosolizes the liquid.  Nebulizers can be used to deliver up to one hundred milligrams of a given drug, and they are the only aerosol delivery systems that can be approved separately from the drugs that they deliver.

In the future, many advances in inhalation technology will probably involve the patient interface.  Existing technologies are capable of delivering most drugs well when used correctly, but ensuring that patients use the devices as intended is not always easy.  There is a bright future for drug delivery via the lungs, but more needs to be learned about lung biology.                   

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