Assessing the Temperature of Thermally Generated Inhalation Aerosols

Abstract Background: Condensation aerosols are produced when a drug is vaporized and then cools in the inhalation air. Because energy is applied to vaporize the drug, there is a potential concern that the air temperature might not be well tolerated. A literature review indicates that the proper metric for this is the wet-bulb temperature (Twb) of the inhaled air. Twb measures the total energy of the air, including moisture content, and reflects the potential impact on safety and tolerability. Methods: The Staccato® system (Alexza Pharmaceuticals, Mountain View, CA) uses thermal vaporization for aerosol generation and was used in a series of studies to characterize the peak transient value (peak Twb) of the air coming out of the device. These studies evaluated peak Twb over a range of air flow rates (15–45 L/min), ambient conditions [15–30°C and 15 to 90% relative humidity (RH)] and vaporization temperatures. Results: Under nominal conditions (30 L/min air flow, 25°C and 50% RH), peak Twb was 28.8 ± 0.6°C ...