The size of aerosol particles generated by the jet nebulizer is directly proportional to the compressed air flow and the size of the nozzle, and a much smaller particle size can be generated. In clinical settings, larger particles may not be suitable for deep lung deposition. Studies have reported that the size of the aerosol particles generated by the ultrasonic nebulizer is larger than those from a jet nebulizer ( 8, 9). The jet nebulizer uses compressed air to aerosolize the drug solution, whereas the ultrasonic nebulizer uses energy from high-frequency sound waves ( 2, 5). The mesh nebulizer uses a vibrating mesh or plate with multiple apertures to generate a liquid aerosol ( 7). There are three basic types of nebulizers based on the aerosol generator, the jet, the mesh, and the ultrasonic nebulizer. Conversely, nebulizers may have a broader application for different patient groups and diseases, due to ease of use and high patient compliance despite some drawbacks such as long time to nebulization ( 5, 6). These two types of therapy may not be suitable for young children and elderly ( 2, 4). DPI requires a relatively high inspiratory flow rate to delivery an effective mass fraction of fine particles ( 2).
pMDI is released at high velocity and requires a simultaneous inhalation by the patient. There are three types of formulations used for pulmonary delivery: pressurized metered dose inhalers (pMDI), dry powder inhalers (DPI), and nebulizers ( 1– 3). Its advantages include direct administration to the site of action, rapid onset, avoidance of the first pass effect, and higher efficiency of the delivered drug. Pulmonary delivery is an important means for drug administration. These factors should be controlled in the evaluation of inhaled aerosol drug formulations when these instruments are used individually or in combination. We conclude that the ambient environment and the nebulizer have significant impacts on the performance and consistency between these instruments. A poor correlation between the NGI and LD measurements was observed for PARI LC (2.2 μm) ( R 2 = 0.893) and PARI LC (2.9 μm) ( R 2 = 0.878), while a relatively good correlation ( R 2 = 0.977) was observed for the largest particle size nebulizer (PARI TIA (8.6 μm)). The results of the NGI and LD measurements of aerosol generated from three types of jet nebulizers were compared. The particle population with a diameter less than 1 μm was significant at a temperature of 5☌ or at relative humidity >90% however, the same particle population became undetectable when temperature increased to 39☌ or at relative humidity of 30–45%. There was an increase in particle size with higher temperature or lower humidity. In this study, the effect of temperature and humidity on the assessment of the nebulizer particle size distribution (PSD) by LD was investigated, and the consistency between NGI and LD measurements was evaluated. Laser diffraction (LD) and next generation impactor (NGI) are commonly used for the evaluation of inhaled drug formulations.