In vitro comparison of the effect of inhalation delay on the variability of the delivered dose from valved holding chambers
The valved holding chamber (VHC) has been designed to optimize delivery for those using pressurized metered dose inhalers (pMDIs). We tested the effects on delivered dose of increasing delay between pMDI actuation and flow through the VHC, using both anti-static and conventional VHCs. Ten anti-static Diamond (Diamond; Philips Respironics) VHCs, anti-static AeroChamber Plus Z-Stat and conventional AeroChamber Plus (Z-stat and AC Plus; Monaghan Medical Corp.) VHCs were washed and air dried and six HFA albuterol sulfate pMDIs (ProAir HFA, 90 µg albuterol, Teva Specialty Pharmaceuticals LLC) were primed before use. For each run the pMDI was actuated into the VHC, after a delay of 0, 5 or 10 s flow through the VHC and attached filter occurred at an extraction flow rate of 5, 15 or 30 L/min for 10 s. The pMDI was actuated 10 times for each of the 10 VHCs of each brand at each delay/flow rate combination. Drug deposits were analyzed using HPLC. Results are presented as coefficient of variation of the delivered doses. The co-efficient of variation was highest for the conventional VHC for all test conditions. Use of an anti-static VHC can minimize variability (improve reproducibility) in delivered dose under in vitro test conditions.