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An aerosol metered-dose inhaler (MDI)

An inhaler or puffer is a medical device used for delivering medication into the body via the lungs. It is often used in the treatment of asthma.

Medication is most commonly stored in solution in a pressurized canister. The canister is attached to a plastic, hand-operated pump. The standard metered-dose inhaler (MDI) on activating releases a fixed dose of medicine in aerosol form. The correct procedure for using a MDI is to first fully exhale, place the mouth-piece end of the pump into the mouth, and having just started to inhale, depress the canister to release the medicine. The aerosolized medicine is drawn into the lungs by continuing to inhale deeply before holding the breath for 10 seconds to allow absorption into the bronchial walls.

The co-ordination between activating the inhaler and breathing in is critical for effective delivery of the drug into the lungs. This can be difficult in younger asthma sufferers or elderly people with arthritis of their hands, or those with a poor ability to hold their breath for 10 seconds after using an inhaler (again generally the elderly). Some breath-activated inhalers do not require manual activation, but will automatically sense the patient breathing in and deliver the dose. Those will vary as a complete unit or as a complementary device, depending on the Country of which one resides in.

Alternatively a device called an Asthma spacer may be used which is an enclosed plastic cylinder that mixes the medication with air in a simple tube, making it easier for patients to receive a full dose of the drug (see image on right).

A different approach to aerosol-inhalers is the use of finely divided powdered devices. These require a priming procedure to place a standardised amount (dose) of powder ready for the patient to take. The operator puts the release end of the inhaler into his mouth and takes a deep inhalation, holding their breath for 10 seconds. There are a variety of such devices which some patients find easier to use, but others complain that powder-devices provokes them to cough.

The largest manufacturers of inhalers are GlaxoSmithKline (makers of the Advair Discus), Merck, AstraZeneca (makers of Pulmicort and Symbicort) and Boehringer-Ingelheim (makers of Atrovent and Combivent). GSK, Merck, and AstraZeneca manufacture both the medical device and the drug being delivered via inhaler.

• Asthma inhaler

• Recent advances in spray medication technology