BEHAVIOR OF NEBULIZING SOLUTIONS AND SUSPENSIONS

A compressed air source is needed to run a jet nebulizer, its operating pressure affects the aerosol flow through the nebulizer, the quantity of drug and/or solution leaving the nebulizer, and the droplet size. With increasing pressure, the output (gravimetric change during nebulization) will increase and the droplet size decrease. The temperature of the nebulizing solution will decrease by as much as 10-degrees-C due to energy loss from evaporation of droplets. Other important considerations in nebulizer therapy are taste, pH and viscosity of the solution. For those drugs which cannot be dissolved, the nebulizing behavior is different. In nebulizing suspensions, the drug particles must be micronized to a mass median diameter of 1-2mum to give optimal output conditions from jet nebulizers with a droplet size of 3mum mass median diameter. The solid drug particles leave the nebulizer through the medium of the droplets, and when a solid drug particle is larger than the droplet it will become trapped in the nebulizer. This has been illustrated in a separate experiment in which 0.5mg/ml budesonide was nebulized from eight different nebulizers. The droplet size as well as the output - calculated from the quantity of drug remaining in the nebulizer after 10 min nebulization - varied with type of nebulizer. A preferable way of determining drug delivery to a patient is to collect the aerosol on a filter during normal breathing and then analyse the drug content on the filter. Output characteristics can only be used for functional testing of nebulizers and in comparisons of different brands of nebulizers.