A metered-dose inhaler (MDI) is a portable device that delivers specific doses of aerosolized medication directly into the lungs. This self-administered method is widely used for managing various respiratory conditions, including asthma and chronic obstructive pulmonary disease (COPD). MDIs offer a quick and convenient way to deliver medication, ensuring a consistent amount reaches the airways to manage symptoms and improve breathing.
Understanding MDI Inhalers
Each MDI contains a pressurized canister, which holds the medication, and a plastic actuator, or mouthpiece, through which the medication is released. These components work together to ensure a measured dose is dispensed with each activation.
Medications typically found in MDIs fall into several categories. Bronchodilators, such as albuterol, relax airway muscles, making breathing easier. Corticosteroids, like Qvar, reduce airway inflammation, beneficial for long-term control of conditions such as asthma. Some MDIs also contain combination drugs, including both a long-acting bronchodilator and an inhaled corticosteroid, for comprehensive treatment of conditions like asthma and COPD.
How MDI Inhalers Deliver Medication
When the user presses down on the canister, a specific amount of medication is released as a fine mist or spray. This spray is propelled out of the mouthpiece, allowing the user to inhale it directly into their lungs.
Propellants, often over 99% of the delivered dose, are liquefied compressed gases like hydrofluoroalkanes (HFAs). They provide the force to create the aerosol cloud and disperse medication into tiny droplets. The MDI’s effectiveness relies on the user’s ability to synchronize pressing the canister with inhalation, ensuring medication travels deep into the airways rather than settling in the mouth or throat. Even with proper technique, only about 10% to 25% of the medication may reach the lungs, with the rest potentially being swallowed.
Correct Usage and Maintenance
To ensure medication reaches the lungs effectively, begin by removing the cap from the mouthpiece and shaking the inhaler vigorously for 3 to 5 seconds to mix the medication evenly. If new or unused for several days, prime the inhaler by releasing a few puffs into the air as specified in instructions. Next, exhale gently away from the inhaler to empty your lungs.
Position the inhaler upright, placing the mouthpiece in your mouth and sealing your lips tightly around it, taking care not to block the opening with your tongue. As you start to breathe in slowly and steadily, press down on the canister once to release a dose of medication. Continue inhaling slowly and deeply for 3 to 5 seconds, filling your lungs completely. After removing the inhaler from your mouth, hold your breath for approximately 10 seconds, or as long as you comfortably can, to allow the medication to settle in your airways.
A spacer, also known as a valved holding chamber, can improve medication delivery and reduce potential side effects. This tube-like device attaches to the MDI and acts as a reservoir, holding the medication mist for a few seconds after actuation. This allows the user more time to inhale the medication, reducing the need for precise coordination between pressing the inhaler and breathing in, which can be challenging, especially during an asthma attack. Using a spacer can increase the amount of medication reaching the lungs to as much as 25%, while also reducing deposition in the mouth and throat, which can cause side effects like oral thrush or hoarseness from inhaled corticosteroids.
Routine cleaning of the MDI prevents clogging and ensures consistent medication delivery. At least once a week, remove the metal canister from the plastic mouthpiece. Rinse only the plastic mouthpiece and its cap under warm running water for about 30 seconds, then allow them to air-dry completely overnight. Do not get the metal canister wet. If there is any hardened medicine in or around the small hole of the mouthpiece, gently use a toothpick to clear it.
To determine when an MDI is empty, many modern inhalers include a dose counter on the canister, which shows the remaining puffs. If your MDI does not have a counter, you will need to manually track the doses taken. Divide the total puffs listed on the canister by your daily usage to estimate how long the inhaler will last. Even if the inhaler continues to spray after the recommended doses, the amount of medication delivered may no longer be accurate, so replace it once the counter reaches zero or the calculated doses are used up.