Nasal spray advances
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Only around 10–20% of asthma medications are delivered to the lungs because of the barrier-nature of the respiratory tract
and medication loss in the inhaler during the inhalation process. Thus, optimizing inhaler design would go some way to reducing
waste and improving the reproducibility of drug delivery to the lungs. Through our research,1 using the mouthpiece as an example, we have developed a methodology that allows inhaler design to be optimized. I believe
this approach could provide significant advantages compared with traditional inhaler design methods.
Getting the design right
We used a computational and experimental approach to design an optimized mouthpiece for a new prototype inhaler that minimizes
the amount of medication lost on the mouthpiece. The analysis process uses in vitro experimental studies of aerosol performance in an initial prototype mouthpiece to validate developed computational fluid
dynamic (CFD) methods for the aerosol inhaler. We then use the CFD model to quantitatively analyse the relationship between
mouthpiece drug deposition with resulting aerosol transport conditions to identify critical design attributes.
During the design phase, these relationships are used to modify in silico the mouthpiece design to target the desired critical design attributes. The modified design is tested experimentally to verify
agreement with the CFD model predicted deposition, and the CFD and in vitro guided design process repeats as needed to achieve the required mouthpiece performance criteria. Performance of the final
optimized mouthpiece design should then be verified using in vitro experiments. By minimizing the drug deposition within the mouthpiece we can increase the amount of drug available to the
patient for inhalation and increase deposition within the airways.
With our research, we were not looking to develop a generic mouthpiece design; rather we wanted to illustrate a rational design
methodology that would be beneficial during any inhaler design process using this combined computation and experimental analysis
and design approach.
The future?
An optimized inhaler design could reduce the velocity at which the spray is delivered from the inhaler, thereby reducing impaction
deposition on the mouthpiece and the patients' throat. This will improve both drug delivery efficiency and reproducibility.
The next generation of pharmaceuticals to be delivered to and via the respiratory tract may not have the large therapeutic window that is generally seen with today's inhaled drugs. Next generation
inhaler designs that improve drug deposition efficiency and reproducibility may, therefore, be required for the next generation
systemic drugs delivered via the lungs.
Reference
1. M. Hindle and P.W. Longest, "A quantitative analysis and design (QAD) approach to produce an optimized aerosol spray inhaler
mouthpiece," 2009 American Association of Pharmaceutical Scientists (AAPS) Annual Meeting and Exposition (Los Angeles, CA,
USA, 8–12 November 2009).
Professor Hindle's research was presented at the 2009 American Association of Pharmaceutical Scientists (AAPS) Annual Meeting
and Exposition, 8–12 November 2009, Los Angeles, CA, USA.
