Which characteristic describes the use of Meter Dose Inhalers?

The correct answer pertains to the necessary steps before using Meter Dose Inhalers (MDIs). MDIs typically require shaking prior to each use to ensure that the medication is properly mixed and delivered effectively. Shaking helps to distribute the medication evenly within the canister. Additionally, some MDIs need to be "primed," especially if they have not been used for a while or if they are new. Priming involves releasing a few test sprays into the air to ensure the inhaler is working correctly and to deliver an accurate dose when it is actually used.

Other characteristics associated with MDIs, such as requiring extensive preparation, ongoing release of medication, or being used exclusively for emergency treatments, do not accurately represent how they function. Extensive preparation is not typically necessary; MDIs are designed for ease of use. They deliver doses as needed, rather than releasing medication continuously. Furthermore, while MDIs can be used in emergency situations, they are not limited to that context and are often used for maintenance therapy in chronic conditions like asthma or COPD.