Metered-dose inhalers

Metered-dose inhalers (MDIs) are the most common asthma medication delivery systems used. MDIs are relatively easy to use, but children under age five often have difficulty using them effectively.

To use an MDI, the patient first exhales completely, then places the MDI to the lips, forms a seal around the mouthpiece, and presses on the top of the canister to deliver a measured dose of medication while slowly inhaling. After inhaling slowly, the patient holds his or her breath for 5 to 10 seconds. Typically, the patient takes at least two puffs of the medication, and it is recommended they wait 30 seconds between puffs.

An alternative method is to hold the MDI about 2 inches away from the open mouth and perform the same procedure. Although this technique is useful, it has two disadvantages: it is tricky to execute properly, and it deposits more than 80 percent of the medication in the mouth. Medication deposited in the mouth is especially disadvantageous with inhaled corticosteroids: deposition of inhaled corticosteroids in the mouth increases the risk for oral candidiasis (yeast infection). The mouth should be rinsed vigorously with water after administering inhaled corticosteroids.

To reduce amount of medication deposited in the mouth when using an MDI, a spacer device may be used. A spacer device is a chamber that fits on the mouthpiece of the MDI and the patient seals their lips around the opposite end. The patient exhales completely and then "puffs" the MDI, filling the spacer tube or chamber with the medication. The patient slowly inhales, drawing the medication into the lungs. As with the MDI it is important to hold the breath for 5 to 10 seconds afterward. Two advantages to using the spacer device are (1) more medication gets into the lungs and (2) the technique is often easier to master.

Breath-actuated MDIs

Breath-actuated MDIs are a variation on the standard MDI. Instead of projecting the medication into the mouth by pressing on the canister, the patient forms a good seal around the mouthpiece and inhales slowly. The inhalation and breath-hold are the same as with a standard MDI.

The advantage of the breath-actuated MDI system is that it eliminates the need for hand-breath coordination. Getting the right speed of inhalation—some patients find it difficult to inhale slowly—and the fact that not all medications are available for breath-actuated MDIs are disadvantages.

Dry powder inhalers

Dry powder inhalers are used in patients under five years of age. A variety of these are available for specific medications, including beta2 agonists and corticosteroids. They work similarly to breath-actuated MDIs. The patient exhales, then forms a seal with the lips around the inhalation port. Unlike breath-actuated MDIs, however, the patient must inhale rapidly. After inhaling deeply, the patient holds his or her breath for 10 seconds.

Not all medications are available in dry powder inhaler form. Another disadvantage to this system is that medication is lost if one accidentally exhales into the device.


Nebulizers can be used with all classes of inhaled medications but are most commonly used with short-acting beta2 agonists and ipratropium bromide. The medication is placed in a chamber that is connected to an air compressor—powered either by standard electric house current (110 volt) or by a battery. The compressor blows air through the chamber, atomizing the medication so the patient can inhale it through a mouthpiece or facemask.

The main advantage of this system is that it requires essentially no hand-breath coordination on the patient's part. It is best to take slow breaths at normal depth, with occasional deep breaths; but any manner of inhaling that the patient finds comfortable is acceptable. This method of drug delivery has obvious advantages for young children. Unfortunately, the process takes longer than MDI and the equipment is not as portable. It also is more expensive than MDIs or dry powder inhalers.

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 01 Jun 2000

Last Modified: 17 Aug 2015