Which statement best describes a pressurised metered-dose inhaler (MDI)?

• A. It delivers a fixed dose with each actuation
• B. It delivers a variable dose with each inhalation
• C. It does not require coordination
• D. It is a dry powder inhaler

Answer: (A)

A pressurised metered-dose inhaler delivers a fixed amount of drug with every actuation because it uses a metering valve to release a precise volume into a propellant-driven spray. Each puff is a measured dose, so the amount released per actuation is essentially the same, regardless of how hard you inhale. In practice, how much actually reaches the lungs can vary with technique and coordination between pressing the valve and inhaling, which is why spacers can help. This is not a dry powder inhaler, which delivers medication as a powder, and it does require coordination between actuation and inhalation, contrary to the other statement.