Analysis of a diffusion dryer for the respiratory delivery of poorly watersoluble drugs

Purpose. The purpose of this study was to analyze a diffusion dryer as a me ans to remove organic solvents from aerosol particles of poorly water solub le drugs. Methods. Aerosols of methanol, ethanol, and ethyl acetate were generated wi th an ultrasonic nebulizer, and inflow to outflow concentration ratio of va por in a annular charcoal column was determined as a function of time by ga s chromotography at two to four different airflow rates. In addition. the p article transmission efficiency was determined with an ethanol solution of the test compound, budesonide. The results were analyzed with equations ori ginally developed for assessing the loss of drug from intravenous tubing al ong with independent measures of the adsorption isotherm of the vapors onto charcoal. Results. Aerosol production was relatively constant with time, and the tran smission of solid particles through the column occurred with efficiency nea ring 100%. The inlet to outlet vapor concentration ratio was adequately des cribed by a model of three resistances in series composed of the inner tube . the screen mesh, and the charcoal bed. Conclusions. The diffusion dryer was found to be satisfactory for the remov al of methanol, ethanol, and ethyl acetate and the efficiency may be assess ed from the adsorption isotherms on charcoal and the geometry of the dryer.