Establishing standardised methods for comparing aqueous droplet inhalers.

Aerosol inhalers are widely used to deliver drug directly to the respiratory system in patients with respiratory disease. Currently available nebulisers only deliver a proportion of the loaded or charged dose to the patient. The proportion of the charged dose received by the patient can be considered as the inhalable dose and is that part of the dose generated during inhalation and breathed in by the patient. As such, it is important to fully characterise the performance of new nebuliser brands to assess the proportion of the charged dose actually delivered to the patient. Despite the large variety of nebulisers, driver units and formulations currently on the market, often little is known about the performance of new nebulisers in terms of inhalable dose under a variety of breathing patterns and with different drug formulations. The results presented here highlight the variation in performance in terms of inhalable dose and droplet distribution of a breath-enhanced jet nebuliser when tested with a number of formulations and under different breathing patterns. Based on the results presented here we propose that a standard protocol for evaluating the performance of established and developmental nebulisers should include breathing patterns appropriate to the intended use and a variety of test formulations to capture those currently available for nebulisation.