A metered dose inhaler (MDI) is a device that helps deliver a specific amount of medication to the lungs. It is commonly used to treat asthma, chronic obstructive pulmonary disease (COPD) and other respiratory problems.

Each inhaler consists of a pressurized canister of medication and a mouthpiece. Pressing down on the inhaler releases a mist of medicine which is then breathed into the lungs.

There are five parts to an inhaler: the medication, the propellant, the canister, the metering valve and the mouthpiece. Each time the inhaler is used, a precise measured, or "metered," amount of medicine is released, which is then breathed into the lungs. Inhalers can be used by all asthma patients age 5 and older, according to the American Medical Association.

The medication in a metered dose inhaler is most commonly a bronchodilator or a corticosteroid. Other medications less commonly used but also administered by MDI are mast cell stabilizers (cromoglicate or nedocromil).

Benefits of MDIs

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Through inhalation, it takes only five to 15 minutes for short-acting bronchodilators (quick-relief medicine) to have an effect, compared to oral asthma medicines, which can take one to three hours. With an inhaler, there are also fewer medication side effects because the medicine goes right to the lungs and not to other parts of the body. A holding chamber (or spacer device) attached to the inhaler can help make taking the medication easier, for adults and children.

Spacers

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See main article at: Asthma spacer

Spacers are tubes attached to the inhaler that act as a reservoir or holding chamber. They serve to hold the medication that is sprayed by the inhaler. This makes it easier to use the inhaler and helps ensure that more of the medication gets into the lungs instead of just into the mouth or the air. With proper use, a spacer can make an inhaler 20 percent more effective in delivering medicine.

Spacers can be especially helpful to adults and children who find a regular inhaler hard to use. People who use corticosteroid inhalers should use a spacer to prevent getting the medicine in their mouth, which can cause an oral yeast infection.

When does an inhaler need to be replaced?

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A metered dose inhaler contains enough medication for a certain number of puffs which is printed on the canister. Even though the inhaler may continue to work beyond that number of uses, the amount of medication delivered may not be correct. It is important to keep track of the number of times an inhaler was used, so that it can be refilled after its recommended number of uses.

See also

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• dry powder inhaler

Asthma | Medical equipment