Comparison of Outpatient Nebulized vs Metered Dose Inhaler Terbutaline in Chronic Airflow Obstruction: Discussion

Comparison of Outpatient Nebulized vs Metered Dose Inhaler Terbutaline in Chronic Airflow Obstruction: DiscussionTwo recently published studies by Jenkins et al and Gunarwardena et al have demonstrated no clear advantage of nebulizers over metered-do$e inhalers. Jenkins et al studied patients with severe, poorly reversible airflow obstruction comparing equivalent doses of nebulized salbutamol and salbutamol administered by metered dose inhaler. There was no significant difference between the two delivery methods, but it is notable that this study was not strictly blinded in that the placebo nebulizing solution was saline rather than “dummy” salbutamol. The study by Gu-narwardena et al produced similar findings, but used only standard dose regimens of ipratropium bromide.

This study is the first to compare terbutaline administered by nebulizer and metered dose inhaler in a strictly double-blind crossover design with similar testing and smelling dummy terbutaline rather than normal saline solution as the placebo. The doses of MDI and NEB terbutaline chosen produced equivalent degrees of bronchodilatation in a group of eight asthmatic subjects with severe airflow obstruction. The nebulizer dose was twice the MDI dose. Previously published acute response studies have quoted dose equivalent factors for MDI: NEB of 1:1 — 1: 12.5. This wide range presumably reflects the variability in dose delivered to the lungs by different nebulizing systems, that is, differing amounts of bron-chodilator solution remain in the nebulizer, are lost to the environment, or are deposited in the pharynx and large airways. The major factors responsible for these differences in distribution of nebulized solution within airways include the flow rate used to achieve nebuli-zation, the breathing pattern, and the degree of airflow obstruction. It should be emphasized that the dose equivalence of MDI and NEB in our study may not be comparable for other nebulizers because of variations in the delivery of dose to the lungs.