In vitro evaluation of the effect of metered-dose inhaler administration technique on aerosolized drug delivery.

Abstract

The administration of aerosolized metered-dose inhalers (MDIs) to mechanically ventilated patients is labor intensive due to the large number of activations required and the currently recommended 30- to 60-second "wait and shake" between each puff. No studies have been published that assess the relationship between this delay between puffs and drug delivery. To address this issue, we conducted an in vitro, randomized, single-blind study using fenoterol MDI containing technetium-99m pertechnetate. Four modes of MDI administration were tested in triplicate by random sequence. Eight activations of the MDI were performed for each mode according to the following procedures: rapid succession (5 sec apart); 30-second intervals and shaking MDI between two rapid activations; 30-second intervals and shaking between each activation; and 60-second intervals and shaking between each activation. Two closed in vitro systems were designed to collect and measure the radiolabeled aerosol. In the first system, the MDI was activated into a plastic collection container; with the second system, the MDI was administered through an aerosol holding chamber with attached circuit filter positioned on the inspiratory line of the ventilator circuit. Sixty-second intervals between each activation were not tested with the second system. Radioactivity was measured before and after each mode of testing. No difference was found between the various modes of administration other than a 14% decrease in the amount of radioactivity released with the 60-second waiting period between puffs, compared with their rapid succession when using the plastic collection container system. Our results support the hypothesis that the delay after each activation of a MDI may not be necessary.