What is a Metered-Dose Inhaler and How Does it Work?
Last updated: June 2022
If you take any inhaled respiratory medications, chances are you take them with a metered-dose inhaler, which is also referred to as an MDI. An MDI is a pressurized canister of medicine that has a plastic holder and a mouthpiece.1 When dispersed, it provides a pre-measured, invariable dose of a medication. Pressing down on the canister and inhaling the medication (in the form of a mist) into your lungs helps open the airways and lets you breathe easier.
Using the MDI properly will allow you to get the correct dosage of your medication.
How do you use a metered-dose inhaler?
With a valved holding chamber
You can use an MDI with or without a device called a valved holding chamber. This piece attaches to the mouthpiece of the MDI and can make it easier for the medication to get into your lungs. Before you use an MDI, with or without the chamber, many people “prime” the MDI. Priming is when you spray one or more puffs of the medication into the air before you use it.1 This helps to make sure the inhaler is ready to use. Priming can vary depending on what kind of MDI you have, so read the instructions when you get the MDI.
To use an metered-dose inhaler with a valved holding chamber:1
- Take off the cap from the MDI and shake the MDI well
- Insert the MDI into the open end of the chamber that is opposite the mouthpiece
- Put the mouthpiece in between your teeth and close your lips around it tightly
- Breathe out
- Press the canister of the MDI once
- Breathe in slowly through your mouth; if you hear a sound like a horn, you’re breathing too fast
- Hold your breath for 10 seconds so the medicine can reach your lungs
- Repeat for each puff you’re supposed to take, allowing about a minute between each puff
- Replace the cap
Without a chamber
If you are taking a corticosteroid through your MDI, rinse your mouth with water or a mouthwash. Consult your doctor if you’re not sure what kind of medicine it is.
If you’re using an metered-dose inhaler without the chamber, the process is similar:1
- Take the cap off the MDI and shake well
- Breathe out completely
- Put the mouthpiece of the MDI between your teeth and seal your lips around it
- As you slowly breathe in, push down once on the canister
- Keep breathing in, slowly and deeply
- Hold your breath for 10 seconds so the medication reaches your lungs
- Repeat as prescribed, allowing about a minute between puffs
- Replace the cap
If you are taking a corticosteroid through your metered-dose inhaler, a valve should be used.1
Cleaning your metered-dose inhaler
For MDIs with a removable canister, take out the canister and rinse the plastic case under warm water once a week to make sure no holes get clogged. Shake the canister and let it air dry completely. If the canister cannot be removed, wipe the mouthpiece with a cloth or cotton swab.
If you have a chamber, it should also be cleaned weekly. Take off the soft ring and soak the chamber in a bowl of warm water with some dishwashing liquid. Rinse with warm water and air dry – do not use a towel. If the chamber becomes cracked or broken, get a new one.2
Things to remember
Many metered-dose inhalers will have a counter on the canister of how many puffs of medicine are left. Keep an eye on this to let you know when you will need a new canister. If the canister has enough medication for 200 puffs and you use 4 puffs a day, you have an idea of when you’ll need to think about a new canister.
Make sure you get your prescription refilled several days before your canister is empty, so you don’t run out by accident.
If you only use your MDI as a rescue inhaler, like with an asthma attack, and not every day, your doctor might be able to give you an extra prescription for an MDI.3 Since you won’t use the inhaler on a regular basis, it can be hard to predict when you’ll run out – but if you have a second prescription on hand, you won’t have to worry about that.
Even though it’s not taken like a typical medication, it’s still medication. If you notice any side effects or have any questions about its use, talk with your doctor about your concerns.
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