JOURNAL OF AEROSOL MEDICINE Volume 15, Number 4, 2002 © Mary Ann Liebert, Inc. Pp. 379–385 In Vitro Effect of a Holding Chamber on the Mouth–Throat Deposition of QVAR ® (Hydrofluoroalkane-Beclomethasone Dipropionate) MUHIB F. RAHMATALLA, Ph.D., 1 PETER C. ZUBERBUHLER, M.D., 2 CARLOS F. LANGE, Ph.D., 1 and WARREN H. FINLAY, Ph.D. 1 ABSTRACT Experimental work has been conducted on the effect of an add-on holding chamber (Aero- chamber ® ) on the characteristics of deposition in a mouth–throat model using 100-mg hydro- fluoroalkane-beclomethazone dipropionate (QVAR ® ) metered dose inhalers at inhalation flow rates of 28.3, 60, and 90 L/min. A filter or cascade impactor downstream of the mouth–throat collected aerosol not depositing. The results emphasize the important well doc- umented effect of a valved holding chamber (VHC), 12 in reducing drug deposition in the mouth–throat. This reduction is largest (24% of nominal dose) at the lowest flow rate tested, becoming insignificant at 60 L/min. Total amount of drug delivered distal to the mouth–throat increases with flow rate both with and without a holding chamber, increasing from 42% to 69% of the nominal dose without a VHC as the inspiratory flow rate increases from 28.3 to 90 L/min. The effect of the holding chamber on post mouth–throat delivery was small, reach- ing significance only at the highest flow rate (90 L/min), where an increase by 8% of the nom- inal dose was observed. No significant effect on MMAD of beclomethasone-dipropionate oc- curred when the holding chamber was used. An argument based on the interaction between induced turbulence and particle inertia is used to shed light on the above observations. Key words: MDI, metered dose inhaler, spacer, aerosol, extrathoracic 379 INTRODUCTION H OLDING CHAMBERS are used with metered dose inhalers (MDIs) to reduce extrathoracic deposition and to alleviate patient coordination issues associated with synchronizing inhalation and actuation of the MDI. Holding chambers achieve their effect by retaining the aerosol sprayed from the MDI in a reservoir. This allows the momentum of the particulate cloud to decay, causes particle size to decrease due to propellant evaporation, and decreases the need for inhala- tion to begin simultaneously with release of aerosol from the MDI. Many studies to evaluate the effect of spacers have been performed in the past. The objectives of previous studies were ei- ther evaluating different drugs and formulations with different spacers 1–5 or to concentrate on other factors, such as the effect of multiple actu- ations and increasing residence times of drug The 1 Aerosol Research Laboratory of Alberta, Department of Mechanical Engineering, and 2 Cystic Fibrosis and Pe- diatric Pulmonary Clinic, University of Alberta, Edmonton, Alberta, Canada.