Are valved holding chambers (VHCs) interchangeable? An in vitro evaluation of VHC equivalence

The European Medicines Agency (EMA) requires that a specific valved holding chamber (VHC) is designated for use with a given pressurised metered dose inhaler (pMDI). No other regulatory authorities impose similar requirements, implying that VHCs are interchangeable. This in vitro study, employing EMA assessment criteria, assessed the equivalence of four anti-static VHCs (aVHCs) versus the non-conducting VHC most widely referenced in pMDI monographs, the AeroChamber Plus™ (AC+) VHC.

The "reference" AC + VHC was prepared by soaking in detergent solution. The four test aVHCs (AeroChamber Plus™ Flow-Vu™ [AC + FV]; Compact Space Chamber Plus [CSC+]; InspiraChamber [IC]; OptiChamber Diamond™ [OCD]) were tested "out-of-packet". Twenty devices of each type were evaluated. A salbutamol pMDI was actuated into each VHC with a 2-s delay between actuation and Andersen Cascade Impactor (ACI) sampling. Drug deposition in four ACI particle size groups was assessed: Group 1, >5.8-10 μm; Group 2, >3.3-5.8 μm; Group 3, >1.1-3.3 μm; Group 4, ≤1.1 μm. Equivalence versus the reference VHC was demonstrated where the 90% confidence interval for the test/reference mass ratio was within 85-118%.

The mass retained within the VHC was similar for the AC + VHC and AC + FV aVHC, but was approximately twice as great for the other aVHCs. Salbutamol deposition in all ACI groups with the AC + FV aVHC was equivalent to the reference AC + VHC. By contrast, deposition in ACI groups 1 to 3 with the CSC+, IC and OCD aVHCs was inequivalent to (approximately half that of) the reference VHC. Inter-device variability for each VHC type was greatest for the IC and least for the AC + VHC and AC + FV aVHC.

The performance of VHCs that superficially resemble one another may differ markedly. Thus, as implied by EMA guidelines, VHCs should not automatically be considered to be interchangeable.