--- title: "Metered-Dose Inhaler | Intro to Pharmacology" description: "Metered-dose inhaler (MDI) is a device that delivers a measured aerosol dose of lung medicine, used in Intro to Pharmacology for asthma and COPD treatment." canonical: "https://fiveable.me/introduction-to-pharmacology/key-terms/metered-dose-inhaler" type: "key-term" subject: "Intro to Pharmacology" unit: "Unit 8" --- # Metered-Dose Inhaler | Intro to Pharmacology ## Definition A metered-dose inhaler (MDI) is a handheld device that delivers a measured dose of medicine as an aerosol to the lungs. In Intro to Pharmacology, it is a common way to give bronchodilators and corticosteroids for asthma and COPD. ## What It Is A metered-dose inhaler, or MDI, is a drug delivery device that gives a set amount of medicine straight into the airways as a fine spray. In Intro to Pharmacology, you usually see it when the course covers inhaled drugs for asthma and COPD, especially bronchodilators and inhaled corticosteroids. The big idea is local delivery. Instead of putting the medicine into the whole bloodstream right away, the MDI sends it into the lungs where it can act faster and use a smaller dose. That is one reason inhaled drugs are so useful for respiratory disease: the target organ is right there in the chest, and the medication can start working before a pill or injection would. An MDI has a canister, a mouthpiece, and a propellant that pushes the medication out as a mist. The device is designed to release a specific amount with each puff, but that only works well if the person uses it correctly. If you inhale too early, breathe in too fast, or do not coordinate the puff with your breath, much of the medication hits the mouth or throat instead of reaching the lungs. That is why technique matters so much. A common sequence is to shake the inhaler, breathe out fully, place the mouthpiece in the mouth, press the canister, and inhale slowly and deeply. After inhaling, holding the breath for a few seconds gives the particles time to settle in the lower airways. If a student sees a case question about poor symptom control, bad inhaler technique is one of the first things to check. Many patients use a spacer with an MDI because it makes coordination easier and improves drug delivery. This is especially helpful for children, older adults, or anyone who has trouble syncing the puff with the inhale. In pharmacology, MDIs are often paired with rescue medicines for quick relief or maintenance medicines for long-term control, so the device shows up in both acute and chronic treatment plans. ## Why It Matters Metered-dose inhalers matter because they connect drug form to drug action, which is a major theme in Intro to Pharmacology. The same medicine can behave differently depending on whether it is inhaled, swallowed, or injected, and the MDI is a clear example of how route of administration changes onset, dose, and side effects. This term also helps you make sense of asthma and COPD treatment plans. A bronchodilator in an MDI can relieve airway narrowing quickly during a flare, while an inhaled corticosteroid may be used more regularly to reduce inflammation over time. When you know the device, you can better explain why one medication is used as a rescue option and another as maintenance therapy. MDIs also show up in questions about patient teaching and medication safety. Poor technique can make a prescribed dose less effective, so you may be asked to spot the reason a patient is not improving even though they are “using” the inhaler. That kind of reasoning is very pharmacology-centered: the drug is only useful if it reaches the target site in the right amount. Finally, MDIs give you a practical way to connect dosage, delivery, and adherence. A device that is compact and portable is easy to carry, but it still requires correct use, cleaning, and sometimes a spacer. Those details often come up when comparing inhalers, interpreting a case, or explaining why a treatment plan is chosen for a specific respiratory patient. ## Connections ### Bronchodilator Many bronchodilators are delivered with an MDI, especially when a patient needs quick relief from bronchoconstriction. The device gets the drug to the lungs fast, which matches the goal of opening the airways. In respiratory case questions, the inhaler is often the delivery method and the bronchodilator is the drug inside it. ### Spacer A spacer attaches to an MDI and makes inhalation easier by holding the aerosol cloud for a moment. That means less medication is lost in the mouth and more reaches the lungs. If a patient has trouble coordinating a puff with breathing, the spacer can improve how well the inhaler works. ### Corticosteroids Inhaled corticosteroids are often given through an MDI for long-term airway inflammation control. This is different from rescue medicines, because the goal is prevention, not immediate relief. In pharmacology, that distinction helps you tell maintenance therapy from acute symptom treatment. ### [Combination Therapies](/introduction-to-pharmacology/key-terms/combination-therapies) Some inhalers combine more than one medication in a single device, so an MDI can be part of a combination therapy plan. That setup is common when one drug handles airway opening and another reduces inflammation. It also reduces the number of devices a patient has to manage each day. ## On the AP Exam A quiz question might show an inhaler image and ask you to identify why the patient is not getting the full dose, or which step in the technique is missing. You may also be asked to match an MDI with the correct respiratory drug class, such as a bronchodilator or corticosteroid. In case-based questions, the skill is recognizing that symptoms staying bad after "using the inhaler" could point to poor technique, no spacer, or the wrong medication type. If the question compares treatment choices, the MDI is usually part of the route-of-administration reasoning, not just the drug name. ## metered-dose inhaler vs Spacer An MDI is the inhaler that holds and releases the medication, while a spacer is an add-on chamber that helps the patient inhale it more effectively. They work together, but they are not the same device. If you see a question about the medicine being delivered, think MDI. If you see a question about improving coordination or reducing loss in the mouth, think spacer. ## Key Takeaways - A metered-dose inhaler delivers a measured aerosol dose of medicine directly to the lungs. - In Intro to Pharmacology, MDIs are most often used for asthma and COPD medications like bronchodilators and corticosteroids. - Correct technique matters because poor timing or breathing can keep the drug from reaching the lower airways. - A spacer can improve delivery, especially for children or anyone who has trouble coordinating the puff and the inhale. - MDIs are useful for both rescue treatment and long-term control, depending on the medication inside them. ## FAQs ### What is a metered-dose inhaler in Intro to Pharmacology? A metered-dose inhaler is a handheld device that releases a fixed amount of medication as a fine spray into the lungs. In pharmacology, it is a common route for inhaled respiratory drugs because it delivers medicine right where asthma and COPD symptoms happen. ### How does a metered-dose inhaler work? The canister holds medicine mixed with a propellant, and pressing it releases a measured puff of aerosol. When the patient inhales at the right moment, the particles move down into the airways and can act locally in the lungs. ### What is the difference between an MDI and a spacer? The MDI is the inhaler that contains and sprays the medication. A spacer is a separate attachment that holds the aerosol briefly so the patient can breathe it in more easily and get more medicine into the lungs. ### Why does inhaler technique matter so much? The dose only works well if it reaches the lungs. If the patient does not shake, exhale, press, inhale, or hold the breath correctly, more medication ends up in the mouth or throat and less reaches the airway. ## Related Study Guides - [8.1 Drugs used in the treatment of asthma and COPD](/introduction-to-pharmacology/unit-8/drugs-treatment-asthma-copd/study-guide/uL6eVk89lhRTJ8i0) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/introduction-to-pharmacology/key-terms/metered-dose-inhaler#resource","name":"Metered-Dose Inhaler | Intro to Pharmacology","url":"https://fiveable.me/introduction-to-pharmacology/key-terms/metered-dose-inhaler","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/introduction-to-pharmacology/key-terms/metered-dose-inhaler#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:23:32.792Z","isPartOf":{"@type":"Collection","name":"Intro to Pharmacology Key Terms","url":"https://fiveable.me/introduction-to-pharmacology/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/introduction-to-pharmacology/key-terms/metered-dose-inhaler#term","name":"metered-dose inhaler","description":"A metered-dose inhaler (MDI) is a handheld device that delivers a measured dose of medicine as an aerosol to the lungs. 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