Improved laboratory test methods for orally inhaled products

Existing pharmacopeial methods for the in vitro testing of orally inhaled products (OIPs) are simplified representations of clinical reality, as their objective is to provide metrics that are discriminating of product quality. Attempts to correlate measures such as fine particle fraction <5 µm aerodynamic diameter with in vivo measures of lung deposition have therefore been notoriously difficult to achieve. Although particle imaging-based techniques may be helpful to link in vitro to in vivo data as surrogates for clinical responses, a reappraisal of the purposes for laboratory-based testing of OIPs is required. This article provides guidance on approaches that may be helpful to develop clinically appropriate methods to assess OIP performance in the laboratory, with the ultimate goal of developing robust in vitro-in vivo relationships for the major inhaled drug classes.