Copley Scientific CEO Mark Copley discusses the recently published USP Chapter <1602> for testing “Spacers & Valved Holding Chambers Used with Inhalation Aerosols”
Q: What does this new USP Chapter cover?
A: Chapter <1602>, published by the United States Pharmacopeia (USP) in 2017, defines standardized methods for characterizing the in vitro performance of a given metered dose inhaler (MDI) with a particular spacer or valved holding chamber (VHC) and calls for testing facemasks to better reflect clinical practice.
Specifically, the chapter includes test methods for assessing the influence of a spacer or VHC on the emitted dose (ED) of an MDI and for characterizing aerodynamic particle size distribution (APSD) performance of an MDI equipped with a spacer or VHC. These methods use test parameters that reflect the clinical conditions within specific patient groups.
Q: Why was this chapter necessary?
A: Previously, the standard USP MDI testing methods made no allowances for add-on devices, even though experts long recognized that the use of spacers and VHCs, which is common among certain patient groups, directly influences in vivo deposition of inhaled drugs. A Canadian Standard, which was the first to define clinically appropriate test methods for testing spacers and VHCs, was published in 2002. A 2011 revision of that standard formed the basis of Chapter <1602>.
A spacer consists of an open-ended tube with a mouthpiece or a facemask at one end and an orifice for interfacing the inhaler mouthpiece at the other. VHCs incorporate an additional one-way valve at the mouthpiece or facemask end of the chamber that ensures the dose is held in the chamber prior to inhalation and prevents the evacuation of the chamber if the patient unintentionally exhales.
The use of spacers and VHCs, with or without facemasks, allows pediatric, geriatric, and infirm patients who may have difficulty coordinating inhalation with actuation of the MDI, to use tidal breathing to inhale the drug dose. VHCs may be preferred by clinicians in large part because they allow for inhalation that is either coordinated (inhalation at the same time as actuation) or uncoordinated (inhalation a short time after actuation).
