The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

ALBUTEROL EMITTED FROM A METERED DOSE INHALER: EFFECT OF PRIMING AND TAIL-OFF.

Susan Lagambina, RRT; Dean R. Hess, PhD, RRT, FAARC. Massachusetts General Hospital and Harvard Medical School, Boston MA.

Background:Albuterol is a rescue medication commonly used by patients with reactive airways disease. This may result in infrequent use. We conducted this study to determine the effect of priming and tail-off on the delivered dose from a pressurized metered dose inhaler (pMDI).

Hypothesis:
The albuterol dose delivered from a pMDI is affected by priming and tail-off.

Methods:
An Anderson Cascade Impactor was used to measure the aerosol emitted from the pMDI. Per manufacturer's instructions, the cascade impactor was operated a flow of 28.3 L/min. The pMDI was held in a vertical position and actuated into the throat of the impactor. Each stage of the impactor was washed with 0.1 N NaOH and assessed for albuterol by spectrophotometry at 243 nm. Albuterol concentration was determined from a standard curve. The total emitted dose was determined by adding the amounts of albuterol deposited on each stage. The fine particle mass was defined as the amount with a mass <4.7 microns. From the priming experiment, 3 new albuterol pMDI (Warrick Pharmaceuticals, Reno NV; nominal dose 90 mcg, 200 actuations) were evaluated. Each was shaken before actuation and several minutes were allowed between actuations. They were assessed new, after 24 hrs of no use, and after 1 wk of no use. For 1 pMDI, tail-off of the dose when it was nearing empty was also assessed.

Results: A summary of the results are shown in the figures. There was a significant difference between actuations for the dose emitted from the pMDI (P<0.001) and the fine particle mass (P<0.001). There was no significant difference between the new pMDI, after 24 hrs of no use, and after 7 days of no use for total dose emitted (P=0.46) and for fine particle mass (P=0.21). When the pMDI neared the end of the labeled number of 200 actuations, there was a rapid tail-off in delivered dose - even though the pMDI delivered a total of 217 actuations.



Conclusions: These data show the importance of priming an albuterol pMDI before use. Two actuations need to be wasted for adequate priming. This occurs within as little as 1 day of no use. In addition, there is a rapid tail-off in dose when the number of labeled actuations is reached.

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