Surface Active Drugs Significantly Alter the Drug Output Rate from Medical Nebulizers

Background: Surface tension of aqueous solutions has a great impact on the resulting size of the produced aerosol droplets. Nevertheless, little attention has been drawn so far to the drug output of surface active substances during nebulization.

Methods: Six nebulizers with three different nebulization mechanisms were operated on the breath simulator and the dependence between the type of aerolisation mechanism, concentration of surface active substance and output rate was investigated.

Results: The results of this study confirm that surface active substances significantly affect nebulization. During ultrasonic nebulization of surface active substances a decrease of the residual drug concentration occurs. Simultaneously, higher amounts of aerosolized substance were observed in in vitro studies. These findings were dependent on the saturation of the liquid-air interface with molecules of a surface active substance. During jet nebulization, nevertheless, the process of an incorporation of substance molecules into aerosol droplets is associated with a strong solvent evaporation from the reservoir. In this case the resulting residual concentration and the aerosolized substance amount are dependent on the outbalancing of either an up-concentration of the surface active substance in the reservoir or rate of solvent evaporation. Vibrating membrane mechanism to nebulize solutions were observed to have minimal effects on the aerosolized substance quantity and residual concentration during nebulization.

Conclusions: Following conclusions for an efficient nebulization delivery of drugs with surface activity with respect to optimal delivery device can be made. Generally, ultrasonic devices produce higher drug output rates within shorter periods of time as compared to jet and vibrating membrane nebulizers. Accordingly, prescription instructions have to be adjusted to these findings. The study also emphasizes that aqueous nebulizer solutions should preferably be prescribed in conjunction with a specific nebulizer which has been tested in vitro and been used in in vivo studies, rather than to let patients choose their delivery device themselves.