SIZE ASPECTS OF METERED-DOSE INHALER AEROSOLS

Abstract

The aerodynamic size distribution of several bronchodilator and corticosteroid metered dose inhaler (MDI) aerosols was estimated in both dry and humid (90% RH) air environments with a 6-stage cascade impactor. The distribution of aerosol size that penetrated into a simulated lung model were also measured. The size distributions were approximately log-normal and ranged from 2.4-5.5 .mu.m in mass median aerodynamic diameter (MMAD) with geometric standard deviation (GSD) of 1.7-2.5 in a dry environment. In humid air, MMAD increased from 1-26% above the dry air state, but GSD remained unchanged. The size of aerosol delivered by MDI that penetrated into a simulated lung model fell to 2.4-2.8 .mu.m in MMAD (GSD, 1.9-2.2). In contrast to aerosols produced by MDI, MMAD of an aerosol of cromolyn sodium powder dispersed by a Spinhaler increased rapidly with increasing humidity, 5.6 .+-. 0.3 .mu.m in dry air and 10.1 .+-. 0.8 .mu.m in 90% RH air. The factors influencing size of MDI-delivered aerosols, including formulation, canister pressure, physicochemical properties of propellants and design of the valve and actuator orifices are discussed. Effective delivery of MDI-generated aerosols into the lung is highly dependent on particle dynamics and jet flow, and no single parameter can produce a unique particle size and jet pattern.