Foster^sup ^: A High-Efficiency Combination Metered Dose Inhaler with Consistent Particle Size Distribution at Alternative Flow Rates

This publication adds perspective to a recent publication by Johal et al. that presented the performance of combination inhalation therapies at a flow rate differing from that recommended by the regulatory authorities for metered dose inhaler (MDI) performance testing. Altering the flow rate through an impactor can create potential pitfalls which can result in performance misrepresentation. In-house data for Foster^sup ^ (Chiesi, Parma, Italy) and Flutiform^sup ^ (Bard Pharmaceuticals Limited, Cambridge, UK) have been collected using standard pharmacopaeial conditions and also at the unconventional 60 L/min flow rate utilized by Johal et al. A marked reduction in mass median aerodynamic diameters (MMADs) of both the inhaled corticosteroids (ICS) and long-acting beta agonists in Foster MDI from approximately 1.2-0.5 [mu]m with increase in flow rate (Johal et al.) is not observed. Use of the Andersen cascade impactor at flow rates above 28.3 L/min is not common practice. The industry generally utilizes data from the next generation impactor (NGI), an impactor specifically designed and developed for this purpose. Data for the ICS component of Foster have been generated using an NGI operated at 30 and 60 L/min, yielding an MMAD (±SD) of 1.1 ± 0.1 [mu]m at both flow rates. Johal et al. suggest that submicron particles are prone to be exhaled by the patient, and therefore imply that they may be non-effective. However, therapeutic significance of submicron particles is supported by a scintigraphic lung deposition study carried out using the Foster MDI. The in vivo data highlight that just 2-3% of the nominal dose was exhaled, with 31-34% deposited in the lungs. Consistent particle size distribution of both active drug components delivered from Foster MDI at flow rates of 28-30 and 60 L/min is observed.