What is the primary method of drug delivery via a metered-dose inhaler?

The primary method of drug delivery via a metered-dose inhaler is based on the use of compressed gas. Metered-dose inhalers (MDIs) function by utilizing a propellant, which is typically a compressed gas, to aerosolize the medication. When the inhaler is activated, the propellant expels a specific, measured dose of the medication in the form of an aerosol that patients can inhale directly into their lungs.

This method allows medications, particularly bronchodilators and corticosteroids, to act rapidly by targeting the airways directly, providing fast relief from respiratory conditions. The accuracy of dosing with MDIs is achieved through this controlled mechanism that ensures patients receive the exact amount of active ingredient intended for therapeutic effect.

Other methods listed, such as breath-actuated delivery, are designed to enhance usability and efficiency but are generally not the defining characteristic of the standard metered-dose inhaler. Liquid spray would pertain to nebulizers or other forms of nebulization rather than MDIs. The tablet form represents oral administration, which is distinctly different from inhalation therapies.