Metered dose inhalers (MDIs) may look simplistic, but the technology inside that shiny canister is really quite sophisticated. With each puff, a precise amount of pressurized medication leaves the canister, ready to be inhaled deeply into irritated, swollen and inflamed airways. As one dose exits the canister, the next takes its place in the metering chamber.
Although different brands may look alike, MDIs are unique by design. Medications, propellants, valves and other components influence both function and effectiveness. The more you know about caring for your inhaler, the more you’ll be able to rely on consistent and effective treatment.
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Take a look at the Patient’s Instructions for Use that came with your MDI. If you can’t find it, ask your pharmacist for a new one or go online, using the name of your medication as a search word. The first instruction you’re likely to see is “Shake the inhaler well immediately before each use.” This important step mixes the ingredients in the canister so that each dose contains just the right blend of medication, propellant and other ingredients. The second instruction is similar: “Prime the inhaler before use.”
When the MDI is brand new or has not been used for a while, the medication may separate from the other ingredients in the canister and the metering chamber. Shaking the MDI will mix the ingredients in the drug reservoir but may not produce enough turbulence to reblend the ingredients in the metering chamber. Priming, or releasing one or more sprays into the air, ensures your next dose will contain the labeled amount of medication.
Even if you’ve been using an MDI for years, you should always check the instructions for details on priming. Each inhaler has a different set of recommendations.
To understand the importance of cleanliness, pick up a used inhaler. Remove the mouthpiece cap and look inside the actuator. Do you see the tiny exit hole where the medication comes out? Is there white, crusty residue forming around the hole? If so, you are looking at crystalline medication. When dried crystals accumulate around the hole, less medication gets through to the airways. Always clean the actuator exactly as directed in the patient’s instructions.
Most should be cleaned weekly, but a few recommend daily cleanings.
Although cleaning is important for all inhalers, it is particularly so with some of the new HFA inhalers. In some cases, the residue that forms around the exit hole may actually block the spray altogether if the inhaler is not kept clean.
Valved Holding Chambers
Many physicians suggest using a valved holding chamber or spacer with your MDI. There are many different brands and models available for patients of every age, from infant to elderly. Your physician can recommend the one that works best with your inhaler. Both spacers and holding chambers extend the mouthpiece of the inhaler and direct the medication toward the mouth. A valved holding chamber has an extra feature that can be helpful to people who have problems inhaling the medication while spraying the device: a one-way flap that traps and suspends medication long enough for you to inhale over 3-5 seconds. Many use a universal rubber end piece to accommodate the MDI without having to remove the canister from the actuator. Some also have a flow-sensing device that helps you learn to control the speed and depth of your inhalation. It is important to follow manufacturers’ instructions for cleaning your valved holding chamber or spacer. Washing your valved holding chamber before initial use will help reduce static charge. Look for continuing improvement in valved holding chamber technology to correspond to new HFA MDIs.