Objective: To assess the reliability of dosing through two budesonide multidose dry powder inhalers (DPI) as derived from the in-vitro variability of the fine particle dose (FPD) and the in-vivo variability of the lung deposition at different flow rates.
Methods: The same two DPIs [device N (Novolizer) and device T (Turbuhaler)] were compared in both studies. In the in-vitro study, the variability of the FPD, measured at flow rates of 30-100 L/min, was determined for equal flow rates and at comparable maximal inspiratory pressures (MIP). In the in-vivo study in healthy subjects (scintigraphic, randomised, crossover design) the variability of the lung deposition was determined at targeted flow rates of 45, 60 and 90 L/min for device N, and at 60 L/min for device T.
Results: The variability of the FPD was lower with device N than with device T by 34%-86%. The differences were statistically significant for flow rates of 60, 70, 90 and 100 L/min (not significant for 40, 50 and 80 L/min) in the in-vitro study. Results for comparable MIPs showed analogous differences (79%, p = 0.004, at the clinically relevant MIP of 4.5 kPa). The variability of the lung deposition was clearly lower with the device N than with the device T. The difference was statistically significant (p = 0.029) at a comparable targeted flow rate of 60 L/min.
Conclusions: Thus, this study showed that device N is likely to improve the reliability of inhalation therapy by reducing both the variability of the delivered drug and that of the lung deposition. The reliability of inhalation therapy and consequently the quality of long-term control of asthma and the patient's compliance might improve when choosing the DPI with the better characteristics.