The Flexineb Metered Dose Inhaler (MDI) system provides a method of administering aerosolised drug from human based MDIs (puffers) to the pulmonary system of the horse. This is achieved by means of a unique handheld equine aerosol spacer or holding chamber which in turn will connect with the equine interface adaptor. When the MDI is actuated by the caregiver, aerosol is captured in the aerosol spacer or holding chamber and made available for inhalation by the horse through the interface adaptor. This system delivers drugs using existing approved drug-device combination human MDIs (eg. bronchodilators and corticosteroids only).