Metered dose inhaler

A metered dose inhaler (MDI) is a drug administration device which, when triggered, delivers a specific quantity of drug for inhalation, usually by means of a calibrated release of compressed gas through a drug reservoir. There may be a simple mouthpiece through which the patient inhales the drug, although this takes a certain amount of training and coordination. Increasingly, the dose is sprayed into a "spacer" chamber through which the patient can breathe, absorbing the vaporized dose. In veterinary medicine and sometimes pediatrics, the inhalation chamber may cover the face or even the head.

MDIs require active cooperation by the patient, or at least the ability to breathe through a mixing chamber. This requires respiratory effort, and, if the patient is in severe respiratory distress, it may be necessary to administer the drug through a nebulizer if the patient is breathing, or through an artificial ventilator if not.

Drugs administered by MDI are most commonly for airway disease: upper airway as for asthma and lower airway as for chronic obstructive pulmonary disease. Classes of drugs in common use include:

• beta-adrenergic agonist, both short-acting such as albuterol and long-acting such as salmeterol
• corticosteroids
• anticholinergics such as ipratropium bromide
• mast cell desensitizers such as cromolyn sodium