. Allergopedia

Dictionary of Allergies .. Metered dose aerosol

The inhaled route in the management of asthma and chronic bronchitis is now accepted as having the advantage of rapid onset and the ability to put low doses of drug on to the site of action with the associated reduction in systemic side effects. The metered dose aerosol was introduced over 40 years ago and is still the most frequently prescribed inhaler device. However, after careful instruction only half the patients can utilise this device but with personalised education approximately 80% of patients will be able to use an MDI effectively. Unfortunately about 20% of patients do not have appropriate inspiratory coordination and therefore other devices such as breath-activated inhalers have been developed.

Over the last 15 years there have been a number of dry powder devices. These were initially of single capsule variety with the disadvantages of loading each dose. More recently the development of multiple dose dried powder systems have developed, the disk and the turbuhaler.

The disadvantage of the dry powder is the problems in maintaining the powder dry as humidity may lead to aggregation of small particles and therefore deposition in the mouth. Potentially the other disadvantages is the dry powder delivery systems require an active inspiratory flow rate of at least 30 1/min and maintain inspiration which is larger than the dead space of the airway. Convention has suggested that twice the milligram dosages are required of dry powder for the same efficacy as the metered dose aerosol but this is now disputed. In order to deliver very large doses of inhaled drugs nebulised solutions were introduced driven either by oxygen, air or small compressor pumps. There was considerable variation of the dose delivered but due to the design of the nebuliser and the variation of flow rates but this has been standardized.

Unfortunately nebulised systems are expensive and cumbersome. Recently a small handheld nebulised spray aerosol delivery system has been introduced; this small compact device is a novel addition to the armamentarium of devices. Each system has its advantages and disadvantages, some disadvantages are now considered as advantages.

The metered dose aerosol with a large volume spacer has the advantage in patients with high dose inhaled steroids that any potential for overcoming first pass metabolism by the swallowed portion is reduced because the high particle size usually deposited in the mouth is deposited in the spacer. Unfortunately the metered dose aerosols rely on chlorofluocarbons and therefore may well disappear and with this advantage. The selection of a delivery device is dependent on the patient’s coordination, lifestyle and aims of the therapy given.


Cochrane, G.M.: Innovations in the management of asthma. Symposium XVth Congress of the EAACI, May 11th, Paris 1992.

Γκέλης Ν.Δ. - Λεξικό Αλλεργίας - Εκδόσεις ΒΕΛΛΕΡOΦΟΝΤΗΣ - Κόρινθος 2013

Gelis Ν.D. - Dictionary of Allergies - VELLEROFONTIS Publications - Corinth 2013