Clinical Review ABC of asthma

Methods of delivering drugs

BMJ 2005; 331 doi: (Published 01 September 2005) Cite this as: BMJ 2005;331:504
  1. John Rees, consultant physician (
  1. 1 Guy's, King's and St Thomas's School of Medicine, London SE1 9RT


    Various inhaler devices and formulations have been developed to deliver drugs efficiently, minimise side effects, and simplify use. With the range of devices available nearly all patients can take drugs by inhalation. All the available devices used appropriately can provide adequate drug to the airways. Inhalers should not be prescribed without checking that the patient can use the device satisfactorily. This should be rechecked on subsequent visits as errors can develop and interfere with treatment. Some drugs, such as leukotriene receptor antagonists and theophylline, cannot be given by inhalation.

    Metered dose inhalers

    Inhalers deliver the drug directly to the airways. Even when a metered dose inhaler is used properly, however, only about 10% of the drug reaches the airways below the larynx. Nearly all the rest of the drug gets no further than the oropharynx and is swallowed. This swallowed portion may be absorbed from the gastrointestinal tract, but drugs such as inhaled corticosteroids are largely removed by first pass metabolism in the liver. Absorption directly from the lung bypasses liver metabolism.

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    Inhalers deliver the drug direct to the airways

    The inhaler should be shaken and then fired into the mouth shortly after the start of a slow full inspiration. At full inflation the breath should be held for 10 seconds. The technique should be checked periodically. About a quarter of patients have difficulty using a metered dose inhaler and the problems increase with age. Arthritic patients can find it hard to activate the inhaler and may be helped by a Haleraid device, which responds to squeezing, or be given a breath actuated or dry powder system.

    Breath actuated aerosol inhalers

    Breath actuated metered dose inhalers are available for most classes of drug. The valve on the inhaler is actuated as the patient breathes in. The …

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