A review of the technical aspects of drug nebulization

Nebulizers are widely used for the inhalation of drug solutions in a variet y of respiratory diseases. The efficacy of nebulizer therapy is influenced by a great number of factors, including the design of the device and the ch aracteristics of the drug solution. Incorrect cleaning, maintenance and dis infection procedures may change the nebulizer performance in time, whereas patient factors can influence the lung deposition of the generated aerosol. In this review the technical aspects of nebulization of drug solutions wil l be discussed. Two main parameters are generally used to evaluate the perf ormance of nebulizers: the droplet size distribution of the aerosol and the drug output rate. The droplet size distribution and the drug output rate a re basically determined by the design and user conditions of the nebulizer. A higher gas flow of the compressor in a jet nebulizer or a higher vibrati on frequency of the piezo electric crystal in an ultrasonic nebulizer, decr eases the droplet size. The choice of the type of nebulizer for nebulizatio n of a certain drug solution may initially be based on laboratory evaluatio n. The major part of the mass or volume distribution should preferably corr espond with aerodynamic particle diameters in the range of 1 to 5 micromete r. The intended drug output must be realized within a reasonable nebulizati on time (less than 30 min). From the drug output only a minor fraction will be deposited in the lung. The relation between in vitro and in vivo deposi tion is only partly understood and to date it has not been possible to pred ict drug delivery only from in vitro studies on nebulizers. Therefore, stud ies in patients should be performed before a drug solution for nebulization can be recommended for clinical practice. The mechanical properties of nebulizers are likely to change during use. An average utilization time of nebulizers is not available. Therefore, the pe rformance of nebulizers should be checked periodically. Patient compliance in nebulizer therapy is relatively low. This is partly d ue to the fact that, at present, drug solutions for nebulizers cannot be ad ministered efficiently within a short period of time. More efficient system s should be developed. If possible, nebulizers should be substituted to mor e efficient systems, e.g. dry powder inhalers or metered dose inhalers.