INVITRO EVALUATION OF THE EFFECT OF METERED-DOSE INHALER ADMINISTRATION TECHNIQUE ON AEROSOLIZED DRUG DELIVERY

The administration of aerosolized metered-dose inhalers (MDIs) to mech anically ventilated patients is labor intensive due to the large numbe r of activations required and the currently recommended 30- to 60-seco nd ''wait and shake'' between each puff. No studies have been publishe d that assess the relationship between this delay between puffs and dr ug delivery. To address this issue, we conducted an in vitro, randomiz ed, single-blind study using fenoterol MDI containing technetium-99m p ertechnetate. Four modes of MDI administration were tested in triplica te 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 acti vations; 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 a erosol. In the first system, the MDI was activated into a plastic coll ection container; with the second system, the MDI was administered thr ough an aerosol holding chamber with attached circuit filter positione d on the inspiratory line of the ventilator circuit. Sixty-second inte rvals between each activation were not tested with the second system. Radioactivity was measured before and after each mode of testing. No d ifference was found between the various modes of administration other than a 14% decrease in the amount of radioactivity released with the 6 0-second waiting period between puffs, compared with their rapid succe ssion when using the plastic collection container system. Our results support the hypothesis that the delay after each activation of a MDI m ay not be necessary.