The misconception of using floating patterns as an accurate means of measuring the contents of metered-dose inhaler devices.

BACKGROUND

Patients and physicians have searched for a reproducible method of determining the amount of medication that a metered-dose inhaler (MDI) contains as well as a reliable method of determining when their MDI is empty. Previously, patients have been instructed to float their canister in water, and depending upon the position attained, have been able to estimate the amount of medication within the canister.

OBJECTIVE

To investigate whether the floating patterns of MDIs are a reliable method of determining the contents contained within an inhaler canister, including that of the newer devices containing the non-chlorofluorocarbon (CFC) propellant.

METHODS

Fifteen albuterol sulfate MDIs (Proventil HFA; Schering, Kenilworth, NJ), 15 triamcinolone acetonide MDIs (Azmacort; Rhĵne-Poulenc Rorer, Collegeville, PA), and 15 fluticasone propionate MDIs (Flovent; GlaxoSmith Kline, Research Triangle Park, NC) were obtained from their respective companies. Each device was floated in a clear container full of water before any actuations. The devices were then actuated into the air at 2-minute intervals and each subsequently floated following 25%, 50%, 75%, and 100% of the prescribed number of actuations and its position within the container observed. The canisters were then actuated until no visual spray was produced from the nozzle and again their floating positions within the container observed.

RESULTS

Each of the three MDIs tested had unique floating patterns both before any actuation as well as throughout the various actuations.

CONCLUSIONS

This study demonstrates that the floating method is not an accurate means by which patients can identify the amount of medication contained within an inhaler device. This includes both conventional MDIs containing CFC propellant, as well as the newer non-CFC MDIs.