If you're using a metered-dose inhaler to treat asthma, it's important that you use it correctly. It's easy to make mistakes when using this type of inhaler, even if you've used one before. When used incorrectly, the device may deliver too much or too little medication to your lungs.

To make sure you're taking full advantage of your metered-dose inhaler, follow these steps. Also consider using your inhaler in front of your doctor. He or she can make suggestions on how to improve your technique.

1. Shake the inhaler vigorously five or six times immediately before using it.
2. Remove the cap from the mouthpiece.
3. Check the mouthpiece for dirt and foreign objects, which could be inhaled. If you haven't used the inhaler for several days, discharge one or two sprays into the air before you use it.
4. Consider attaching a spacer tube to the mouthpiece of the inhaler. A spacer is a 4- to 8-inch length of tubing. It helps send more of the medication deep into your lungs instead of depositing it in your mouth, which can lead to harmful side effects. Some inhalers have a spacer built into the unit. For others, you can buy a plastic tube without a prescription at a pharmacy or use a 4- to 8-inch cardboard or paper tube.
5. Hold your head erect and sit up tall or stand. Exhale normally but not forcefully.
6. Close your mouth around the open end of the spacer tube. Make sure your tongue or teeth aren't blocking the opening. If you don't have a spacer tube, place the mouthpiece of the inhaler unit about 2 inches in front of your open mouth.
7. Breathe in very slowly as you squeeze the inhaler once. Don't stop inhaling when you squeeze. Continue to breathe in slowly for several seconds or for as long as it feels comfortable. This process combines the medication with the incoming air and pulls the mix into your lungs very slowly. Remove the spacer tube from your mouth, but don't exhale.
8. Hold your breath for as long as comfortable or up to 10 seconds to help the medication settle in your airways. Exhale slowly.
9. Shake the inhaler before each use.
10. Rinse your mouth with water or brush your teeth after using a corticosteroid inhaler. Spit out the water.

Keep your metered-dose inhaler at room temperature. When in a cold environment, carry the metered-dose inhaler close to your body. Warm the canister by rolling it between your hands before using it. Warming the canister to room temperature produces smaller particles of medication. Smaller particles are better inhaled and distributed throughout your lungs.

If you use your metered-dose inhaler regularly, clean it every day. To clean the device, remove the metal cartridge. Rinse the applicator under running water, paying special attention to the hole — just inside the mouthpiece — where the medication is dispensed. Air-dry the device. Once it's dry, insert the cartridge with a gentle twist. Keep the protective cap on the inhaler when you're not using it.

Because you can't see how many doses of medication are left in your inhaler, plan ahead to replace it before it's empty. To be safe, get the replacement about 7 to 10 days before the old one runs out. As long as you know how many doses of medication a cartridge holds and how many times you use your inhaler per day — or per month, with a quick-relief inhaler — you can predict how long it will last. If you have trouble keeping track, mark your calendar on the date when you start a new inhaler. When you think it might be time for a refill, a glance at the calendar will help you decide.