Are extra-fine particles from dry powder inhalers likely to improve lung deposition?

Rationale: Differences between CFC- and HFA-MDIs include the particle size distribution of the aerosol and the discharge velocity of the aerosol. Because deposition of aerosol particles decreases rapidly in all lung sections with decreasing particle diameter below 1.5 μm, it is questionable whether there is any real advantage from administration of extra-fine particles without the benefit of a low delivery velocity. And although recent reviews have led to the conclusion that there is no convincing evidence yet for increased benefit from the use of extra-fine particles in asthmatic patients, a dry powder inhaler (DPI: Foster NEXThaler) with an extra-fine aerosol output has also now become available. Methods: Fine particle doses (FPDs) from Foster NEXThaler (F-N) measured with the Next Generation Impactor at 2, 4 and 6 kPa were compared with those from Symbicort Turbuhaler (S-TBH), Seretide Diskus (S-D) and Rolenium Elpenhaler (R-E) and evaluated in relation to the corresponding flow rates. Results: Flow rates corresponding with 4 kPa and delivered FPDs as percent of label claim at 4 kPa are summarised in the table. (Figure Presented) Conclusion: The FPD% <1 μm from NEXThaler is much higher than that from the other DPIs. Because this is at about the same flow rate, it is arguable whether this will result in significantly higher lung deposition, as FPD% 1-5 μm from NEXThaler takes an intermediate position between the other DPIs.