Effect of canister temperature on performance of metered-dose inhalers

We studied the effects of ambient temperatures between 0 degrees C and 42 degrees C in an anatomically realistic model of the upper airway ventilated with warm, moist air. Metered-dose inhalers of metaproterenol maintained at the experimental temperatures were activated in the mouth of the model at the onset of inspiration. We measured the amount of drug released and that which was able to penetrate the model at each temperature. At low canister temperatures considerably more drug was released than at higher temperatures. However, at higher temperatures much more drug was able to traverse the upper airway, raising lower airway deposition from 17.7% at 4 degrees C to 32.2% at 37 degrees C. Aerosol size became progressively smaller as temperature was raised: mass median diameter (MMD) was 3.65 microns at 0 degrees C and 2.50 microns at 37 degrees C. These findings are most likely due to greater canister vapor pressures at higher temperatures. We conclude that patients should probably be instructed to prewarm metered-dose inhaler canisters prior to use when canister temperatures are low.