111 Respiratory Drug Delivery Asia 2016 – Wei and Byron Clinically Relevant In Vitro Performance Tests for Powder Inhalers Xiangyin Wei and Peter R. Byron School of Pharmacy, Virginia Commonwealth University, Richmond, VA, USA KEYWORDS: mouth-throat (MT), inhalation profile (IP), in vitro–in vivo correlation (IVIVC), total lung dose in vitro (TLD in vitro ), aerodynamic particle size distribution of TLD in vitro (APSD TLDin vitro ), quality by design (QbD) SUMMARY Predicting drug dose in the lung and its relevant aerosol characteristics for dry powder inhalers (DPIs) is possible by conducting realistic in vitro tests using human mouth-throat (MT) models and inhalation profiles (IPs) that mimic inhaler use in the clinic. Improved in vitro–in vivo corre- lations (IVIVCs) of lung deposition can help drug developers better estimate a DPI’s performance under realistic clinical conditions and identify possible product- or human-related factors that may influence inhaler quality. Budelin® Novolizer® is used to illustrate how realistic in vitro tests can be used to estimate clinical performance of a DPI. Two studies were designed to character- ize the (a) total lung dose in vitro (TLD in vitro ) and (b) aerodynamic particle size distribution of TLD in vitro (APSD TLDin vitro ). When the medium (and extremes) MT and IP were incorporated in inhaler testing, variations of TLD in vivo (ranging from 9.4% to 41.0%) could be predicted from in vitro (TLD in vitro ranging from 9.3% to 44.5%). Results for APSD TLDin vitro also indicated that the inhaler’s clinical performance could be sensitive to subject’s IPs. While the selection of MTs and IPs are yet to be standardized, product development scientists wishing to perform real- istic in vitro tests may need to study possible variations in MT model and IP to fully explore the extent of variability in clinical lung deposition and the associated particle size distributions for their chosen DPI.