November 2002 / Volume 47 / Number 11 / Page 1290
Assessing Nebulizer Performance
IntroductionThe quality of the aerosol generated by a nebulizer system is a function of its design, operating parameters, and the drug formulation to be aerosolized. The aerosolized drug dose inhaled from a nebulizer is determined by the patient's breathing pattern. The site of deposition of the aerosol in the lung is primarily influenced by the inspiratory flow rate and additionally by the nature of the lung disease. Thus, tests of performance that incorporate these different variables will provide data that give a better understanding of overall nebulizer performance. As discussed in this paper, a number of in vitro and in vivo laboratory tests can be undertaken to measure the characteristics of the delivery system as well as the quality and quantity of the aerosolized drug provided. With this information one can estimate the dose of drug that will be inhaled and deposited below the larynx. The accuracy of these predictions can additionally be improved with the use of breath simulators and standard breath patterns. Breath monitors that capture and feed actual patient breathing patterns into the simulator to mimic nebulizer operation during actual patient use further increase the accuracy of dose estimation. With the vast number of nebulizers available and also in development, a comparison of information obtained from different nebulizers is key in making an informed decision when selecting an aerosol delivery system that can provide an efficacious dose of a particular drug to a specific patient population.
In Vitro Tests
Testing for Variability in Manufacturing Between Units
Temperature Change in the Reservoir Solution During Nebulization
Particle Size of the Nebulized Aerosol
Measuring Drug Output Under Simulated or Actual Breathing Conditions
In Vivo Testing
The efficiency of delivery of aerosolized medications varies among nebulizer systems. Differences in the amount of drug aerosolized and the respirable dose provided depend on a number of factors and can be considerable. This may result in different clinical effects, particularly if the aerosol delivery efficiency is poor in comparison to other drug delivery methods or other nebulizers. Similarly, the performance characteristics of a nebulizer used with one type of drug may be different when used with other categories of drugs and potentially with generic formulations of a particular drug. Thus, it would be prudent to measure the output characteristics of a drug from a number of nebulizer delivery systems prior to recommending the use of a specific system or systems for the drug.