Drug delivery devices: Metered dose inhalers and spacers

The metered dose inhaler (MDI) is the most common device people use to take asthma medication. An MDI allows you to inhale a specific amount of medicine (a "metered dose"). It consists of a metal canister, which keeps the medication under pressure, and a plastic sleeve, which helps to release the medication. When you press the canister, medicine particles are propelled toward your throat where you can inhale them.

Proper technique is critical when using an MDI. If your technique is wrong, too much of the medicine can end up in your mouth instead of your lungs, and it will not have enough medicinal effect. Make sure your doctor or nurse reviews the proper technique with you at every visit, since it is common for people to get careless with their technique over time. Check out these instructions for using an MDI.

Even with proper technique, as much as 80% of your dose may end up in your mouth and throat. For that reason, many doctors recommend that you rinse your mouth after using an MDI. This will reduce the bad taste and minimize unnecessary side effects.

The main advantages of an MDI are its compact size, the treatment process only takes a couple of minutes or less, and it is generally as effective as a nebulizer.

Spacers (holding chambers)

MDI spacers, sometimes called "holding chambers," are widely encouraged by asthma educators for people of all ages. Spacers work with your MDI to deliver medication more easily and effectively, and can reduce side effects.

When you use an MDI by itself, more of the medicine is left in your mouth and throat, wasting your dose and causing an unpleasant aftertaste. Spacers hold the "puff" of medicine between you and the MDI, so that you can inhale it slowly and more completely. As a result, more of the medicine gets into your airways. A comfortable mask can be added to the spacer for small children or others who have difficulty maintaining a good lip seal on the mouthpiece.

Breath-actuated MDI

This is another type of MDI that is used with beta-agonist drugs. The device is placed directly in your mouth. It is called "breath-actuated" because you do not have to press anything to release the drug; the drug comes out automatically when you inhale. These MDIs therefore do not require a spacer, nor do they require the specific timing and coordination of pressing a canister and breathing in. This is a device which may be particularly helpful for the elderly, but like all of the other methods it is not a perfect solution. The drug must be inhaled slowly to work, which can be a tricky technique in itself. Breath-actuated MDIs are not as common as other drug delivery methods.


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Review Date: 5/16/2007

Reviewed By: Alan Greene, M.D., F.A.A.P., Department of Pediatrics, Packard Children's Hospital, Stanford University School of Medicine; Chief Medical Officer, A.D.A.M., Inc.

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