Lung Deposition of Fenoterol and Flunisolide Delivered Using a Novel Device for Inhaled Medicines: Discussion
In contrast to the MDI, where drug particles leave the canister at a very high speed and initially are of relatively large particle size (mass median diameter, 15 to 20 |Jim), the RESPIMAT soft mist inhaler generates a slow, gentle release of particles, a high proportion of which are respirable (<5 jmm), and which patients may find easier to inhale in clinical practice. These features of the device suggest that lung deposition may be improved, which has been confirmed by the results of the present studies. The mean whole lung deposition of fenoterol and flunisolide delivered by the RESPIMAT device was similar (39.2% and 44.6% of the metered dose, respectively) More info order antibiotics online. Such high values of whole lung deposition have only rarely been reported previously with other aerosol delivery devices. Lung deposition >25% of the metered dose has been reported for the Turbuhaler, an MDI containing a propellant-soluble radiolabel and an MDI plus Nebuhaler spacer. The whole lung deposition of fenoterol delivered by MDI (11.0%) was similar to the lung deposition from MDIs obtained in other studies. Moreover, the mean whole lung deposition of flunisolide from the MDI with Inhacort spacer (26.4%) was similar to that obtained in other studies using MDIs with larger-volume spacer devices, where relatively high lung deposition values were recorded. Dolovich et al have also observed lung deposition from MDIs used with or without an Aerochamber averaging about 10% of the dose, with oropharyngeal deposition <10%. Inhalation technique has a critical effect on drug delivery to the lungs, but was carefully controlled in these studies, with inhaled volumes, inhaled flow rates, and breath-holding pauses being similar for all devices tested.
Lung deposition calculated as a percent of total body deposition expresses the “selectivity” of delivery to the intended site from inhalation devices. For devices like the RESPIMAT that can produce a high deposition in the lungs, then the amount of oropharyngeal deposition is automatically limited. As a result, a more selective delivery pattern is generated, with a higher proportion of the dose reaching the required site. Consequently, a smaller dose of drug may be needed to produce the required therapeutic effect when a high lung deposition device such as RESPIMAT is used. The combination of the selective targeting of drug to the lung and the possibility of reduced total doses may lead to improvements in the therapeutic ratio of respiratory medicines.