Basic Concept
Metered dose inhalers are used to deliver doses of certain medications directly to the lungs. These inhalers are typically used to treat lung diseases such as asthma and COPD (chronic obstructive pulmonary disease) by delivering medications directly to the lungs. Metered dose inhalers usually are used to administer fast-acting medications that help reduce inflammation of the lungs; these work best if directly inhaled into the lungs. These inhalers consist of a mouthpiece and a special canister that contains both the medication (typically in powder form) and pressurized air, which is used to propel the medication.
Canister
The canister of a metered dose inhaler contains the medication. This canister is also filled with a type of gas called hydrofluorocarbons, special gases that don't react with the medication. When the canister is activated (usually by pressing on the top of it when it's attached to the mouthpiece), a small amount of this gas is released and takes some of the medication with it. This vapor of air and medication is then channeled through the mouthpiece and delivered to the lungs when the patient inhales. Metered dose inhalers are designed so that each usage delivers a precise amount of medication.
Features
Some metered dose inhalers come with a "spacer," a connecting piece that holds the medication in the mouthpiece for longer. This allows the medicine to be inhaled more slowly, which lets more of the medication get to the lungs. Other metered dose inhalers have the mechanism rigged so that the medication is automatically released from the canister when the patient inhales through the mouthpiece. Some metered dose inhalers are equipped with counters that keep track of how many doses are left. This is critical, because the canisters only have a certain amount of medication and the canisters must be replaced periodically.
