Particle Size and Asthma Treatment

Particle Size and Asthma Treatment

Reference: Busse, WW, and Wenzel, SE, May 2000. Large and Small Airway Dysfunction in Asthma: Rationale for Treating the Entire Airway.

Inflammation in the lungs of asthmatics seems most pronounced in small distal airways although central airways also show signs of inflammation. This information was obtained by immunocytochemical, histochemical, and bronchoscopy measurements of respiratory mechanics. The increased inflammation in peripheral airways appears related to hyper responsiveness of these airways. Inflammatory activity in the bronchiolar-alveolar region may also cause airway remodeling, gas trapping, and mucous plugging.

Drs. Busse and Wenzel describe the treatment of smaller airways of asthmatics with MDI's (metered dose inhalers) filled with a new propellant, hydrofluoroalkane (HFA). HFA was developed as an alternative to CFC (chlorofluorocarbon) propellants in an attempt to make a less damaging propellant for the ozone layer. The use of MDI's with beclomethasone diproprionate (BDP) in HFA yields a particle size of approximately ~1.1 um MMAD. In contrast, CFC-BDP yields particles of about 3.5 to 4.0 um MMAD.

The HFA-BDP propellent appears to penetrate the deep lung as a result of less oropharyngeal impaction. Not only does HFA-BDP enhance FEV₁ (forced expiratory volume) more than CFC-BDP in asthmatics but this improved FEV₁ was dose related. The respirable fraction of HFA-BDP is 58% compared to 21-42% for CFC-BDP.

Other treatment modalities such as beta₂agonists and anticholinergic agents appear to have optimal effect with MMAD of <3 um. Thus new advances in the technologies of MDI development may aid in improved long-term treatment and outcome in asthma.

By: Susan G. Shami, ScD