What type of inhaler is considered a metered-dose inhaler (MDI)?

A metered-dose inhaler (MDI) is specifically designed to deliver a precise amount of medication in each puff, utilizing a propellant to aerosolize the medication. This allows for consistent dosing and is crucial for patients who rely on the inhaler's accuracy for conditions like asthma or chronic obstructive pulmonary disease (COPD). The mechanism involves the use of compressed gas, which helps to propel the medication out of the inhaler in a fine mist, making it easily inhaled into the lungs.

In contrast, devices using dry powder do not use propellants and rely instead on the patient’s inhalation effort to draw the medication into the lungs. While effective, they do not fall under the category of metered-dose inhalers. Similarly, nebulizers deliver medication in a different form, producing a mist from liquid medication without the specific dose control provided by an MDI. Lastly, oral sprays, designed for delivering medication via the oral cavity, are distinct from inhalers that target the respiratory system. Therefore, the option describing an inhaler that delivers a specific dose via compressed gas accurately defines a metered-dose inhaler.