Background: The USFDA advocates that manufacturers add Dose Counters or Indicators to pMDIs to provide means for the user to know when to replace their inhaler. Patient handling studies are a key part of the process to confirm the accuracy of such counters/indicators. However, they are challenging to undertake due to compliance issues related to accurate completion of user-diaries, and user/device-induced variability affecting dose delivery gravimetric assessment. This study demonstrates outcomes from simulated use, in which the gravimetric method for assessment of count accuracy was developed to minimize the impact of actuation weight variability, and the effect of varying the offset between the force-to-fire (FTF) of the pMDI and force-to-count (FTC) the indicator was examined.

Materials and Methods:  44 inhaler-dose indicator naïve participants were each allocated 3 pre-weighed placebo pMDIs, each equipped with a dose indicator (AeroCount^® TMAI-200 model, Trudell Medical International, Canada), so that a given user had three pMDIs all having their nominal FTF at 28-N. Each inhaler was mounted with a unique dose indicator that was manufactured to one of three FTC settings (18-N, 22-N and 25-N). During 3-weeks, each participant delivered 6-actuations per inhaler twice daily (12-actuations/device/day).  Canister weight was recorded after every 6-actuations to minimize the effect of user- and device-induced actuation weight variation.

Results: Each pMDI FTF/FTC setting combination was evaluated over at least 7,500 actuations. No undercounting was observed with the 18-N and 22-N FTC settings and an incidence occurrence of only 0.01% was detected with the 25-N setting.  The incidence of overcounting was only 0.3% for both 18-N and 22-N settings and 0.25% with the 25-N setting.

Conclusions: The TMAI-200s evaluated in this investigation were measured to have a total combined discrepancy rate of 0.28% that is well within previously reported figures on other commercially available dose indicators and counters.  The magnitude of the FTC offset within the study limits had minimal effect on performance, demonstrating a robust device design space.