The mainstay of the pharmacological management of asthma and chronic obstructive pulmonary disease (COPD) is the use of inhaled drugs. This route enables drugs to be delivered to the site of their action, minimising the risk of adverse effects caused by systemic absorption. Drugs that can be administered by the inhaled route include the most commonly prescribed drugs for asthma and COPD, namely short and long-acting β2 agonists and anticholinergic drugs and corticosteroids. There are two main types of inhalers: pressurised metered dose inhalers (pMDIs) and dry powder inhalers (DPIs). pMDIs were introduced in the mid-20th century. The active drug is held in suspension or solution in a canister with a propellant. Proper use of pMDIs requires the patient to apply a series of techniques correctly: i) fire the device, releasing the aerosol very shortly after the initiation of inspiration; ii) inspire slowly and deeply;
and iii) hold their breath. Many patients find this procedure difficult. Modifications and add-ons include breath-activated pMDIs and spacers and valved holding chambers; these help to obviate some of the problems with pMDIs. DPIs are breath-activated devices. Following priming, which is different for each
device, the aerosol is generated by the patient taking a deep, rapid inspiration. This de-aggregates the powdered drug from its carrier. A prolonged breath-hold is then required. Many studies have shown that errors that may impair the effective delivery of the drug to the lungs, including critical errors, are very common with both pMDIs and DPIs. Such inhaler misuse has been shown to be associated with poorer symptom control and more frequent emergency department attendances. Errors in the use of inhalers can be a consequence of device-related factors, patient-related factors, and health professionalrelated
factors. Minimising inhaler misuse requires the prescribing physician to choose, in cooperation with the patient, the most suitable device for the individual patient. Education and training with subsequent monitoring and re-training are thereafter crucial. There remains a need for more user-friendly devices, which provide constant doses of the active agent, in addition to built-in dose counters and patient feedback.
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