Following deposition, inhaled drug particles must dissolve and permeate into the lung tissue to reach their site of action. Dissolution testing elucidates this behaviour and is particularly important for modified release or low solubility compounds, or when establishing parity between a test (generic) and reference (innovator) product. Currently published dissolution methods offer limited flexibility with respect to the particle size ranges analysed, tend to suffer from poor reproducibility and have low discriminating power. Inconsistent sample collection is a common problem.

The new IDDC accommodates a range of inlet components routinely used to measure the aerodynamic particle size distribution (APSD) of OIPs by cascade impaction including the standard USP induction port, the Next Generation Impactor pre-separator, the Fast Screening Impactor housing/insert and the Alberta Idealised Throat. Choice of inlet component determines the particle size range captured for dissolution testing. This can be the Impactor Sized Mass (ISM - the mass that would penetrate the first stage of the impactor), the ex-throat dose or the Fine Particle Dose (FPD); the fraction of the dose defined as respirable on the basis of size. The dose is collected on a detachable insert, positioned inside a removable filter holder, at a test flow rate in the range of 30 to 100 L/min, depending on the MDI or DPI under test. This insert can be directly transferred to a USP apparatus 2 for dissolution testing, similar to the established paddle-over-disc method (USP apparatus 5).