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Metered Dose Inhaler (MDI)

This type of inhaler uses a small canister of medicine inside a plastic holder. The medicine in the canister is under pressure. As you press on the canister, a small burst ("a metered dose") of medicine is sprayed out of the canister. Most people call this a "puff" of medicine.

Your doctor will tell you the number of puffs (inhalations) to use, for example one or two puffs for each dose. If you use two or more puffs, it is important to take them one at a time. Because the medicine is sprayed out in a very fast burst, it can be difficult to use the inhaler correctly to get the medicine into the lungs. Using a spacer will help. Spacers must be used with all MDI’s containing corticosteroids (controller medicine) and are recommended for use with all MDI medication. For small children and infants, spacers that have a soft mask attached can be used so the medicine can be breathed in easily.

Since you can't see how much medicine is left in the canister, you need to know how many puffs a canister holds.

Look on the side of the canister or in the package insert that comes with the inhaler and find the total number of puffs (called doses) the canister contains.
Divide the total number of doses in the canister by the total number of puffs you use each day to know how many days the canister will last.
Count out the days on a calendar and note the date the canister will run out of medicine.

Write this date on the canister or on the calendar so you remember to get a refill one week before.
This only works for regular controller medicines.

For rescue inhalers, try to keep a record of the number of puffs you have used (for example, make a mark on the calendar for each time you use it) so you will have some idea about how soon you will need a refill. Don't wait until the canister is empty before getting a refill.