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Review Asthma Inhaler Characteristics in Asthma Martyn Francis Biddiscombe and Omar Sharif Usmani Airway Disease Section, National Heart and Lung Institute, Imperial College London, and Royal Brompton Hospital, London, UK T he history of inhaled therapy goes back a surprisingly long way. More than 4,000 years ago, in India, the vapour of plants from the nightshade family placed on hot bricks was inhaled to alleviate breathing difficulties. The bronchodilators, derived from these plants, and compounds related to them, have played a significant part in therapeutic aerosol delivery over the years and remain important in the treatment of lung diseases today. The development of inhaled therapy has accelerated over the past 60 years with the arrival of the first truly portable inhaler in 1956 to relieve the symptoms of asthma. Initially, only bronchodilators were delivered from these devices, but as the true nature of asthma was revealed, inhaled corticosteroids were introduced to treat the underlying inflammation that is a major component of asthma. Further advances have led to long-acting bronchodilators becoming available, and combination therapies containing both long- acting bronchodilators and corticosteroids in one inhaler. Asthma therapy has come a long way in a comparatively short time with over 230 device and drug combinations available for treating the disease. However, despite enormous investment asthma remains a huge healthcare problem. The number of people with asthma continues to grow with over 300 million people affected worldwide and 250,000 annual deaths attributed to the disease. It affects people of all ages and has a varying degree of severity. In this article, we look at the ideal characteristics for asthma inhalers and highlight some of the most important reasons for the failure of current asthma treatments. Keywords Asthma, inhaler, pressurised metered dose inhaler (pMDI), dry powder inhaler (DPI), nebuliser, soft mist inhaler (SMI), inhaled corticosteroid (ICS), device chracteristics, patient adherence Disclosure: Martyn Francis Biddiscombe has received industry-academic funding from Boehringer Ingelheim, Chiesi and GlaxoSmithKline. Omar Sharif Usmani has received industry-academic funding from Boehringer Ingelheim, Chiesi, Edmond Pharma, GlaxoSmithKline, Mundipharma International, and has received consultancy or speaker fees from AstraZeneca, Boehringer Ingelheim, Chiesi, Cipla, Edmond Pharma, GlaxoSmithKline, Napp, Novartis, Mundipharma International, Pearl Therapeutics, Roche, Sandoz, Takeda, UCB, Vectura and Zentiva. No funding was received for the publication of this article. Compliance with Ethics: This study involves a review of the literature and did not involve any studies with human or animal subjects performed by any of the authors. Authorship: All named authors meet the International Committee of Medical Journal Editors (ICMJE) criteria for authorship of this manuscript, take responsibility for the integrity of the work as a whole, and have given final approval to the version to be published. Open Access: This article is published under the Creative Commons Attribution Noncommercial License, which permits any non-commercial use, distribution, adaptation and reproduction provided the original author(s) and source are given appropriate credit. Received: 7 April 2017 Accepted: 23 May 2017 Citation: EU Respiratory & Pulmonary Diseases, 2017;3(1):32–7 Corresponding Author: Martyn Francis Biddiscombe, Airway Disease Section, Imperial College London, National Heart and Lung Institute, Dovehouse Street, London SW3 6LY, UK. E: m.biddiscombe@imperial.ac.uk 32 Inhalation therapy has long been recognised as the optimal mode of treatment for the majority of patients with asthma and has played a pivotal role in their management for decades. 1 The ability to target drug therapy directly to the site of disease within the lungs maximises local efficacy whilst minimising systemic exposure. Much smaller doses are necessary compared with oral and intravenous treatments reducing the risk of side effects. However, despite huge investment in new asthma drugs and inhalers over the past 30 years, disease control is still unsatisfactory. 2 Part of the explanation lies with the poor response of certain types of asthma to current treatment. Asthma is a highly complex and challenging chronic inflammatory disease of which, despite significant breakthroughs in recent years, our understanding is still far from complete. Indeed, due to its heterogeneous nature, the word asthma may in the future be considered just an umbrella term to define several different phenotypes. 3 Other factors such as not treating comorbidities or poor targeting of inhaled drugs to distal lung regions may also contribute to poor disease control. 4 One of the biggest factors for poor disease control is the patient’s inability to master the use of their inhalers leading to the effectiveness of the treatments being greatly reduced. Indeed, the patient’s ability to use their device correctly should be a key consideration in their therapeutic management, according to the European Respiratory Society. 5 The aims of asthma therapies are to alleviate symptoms by minimising exacerbations and controlling inflammation, and in Europe today there are more than 230 different device/drug combinations of inhaled therapy and many of these are available for the treatment of asthma. 6 The focus of this article is to review the literature regarding current and new inhaler characteristics for treating asthma and investigate the obstacles that must be overcome in order for patients to gain the full benefit from their inhaler. The main inhaler designs will be discussed as well as the most desirable characteristics of the aerosol discharged from the inhaler. We also discuss the reasons why inhaled therapy is not as effective as it could be. Desirable inhaler characteristics for treating asthma Traditionally, there are three main categories of inhaler devices used to treat asthma. These are the pressurised metered dose inhalers (pMDIs), dry powder inhalers (DPIs) and nebulisers. Numerous drug therapies are available in combination with these devices including short-acting 2 -agonists and long-acting 2 -agonists (LABA); short-acting muscarinic antagonists and long-acting muscarinic antagonists (LAMA); inhaled corticosteroids (ICS); and dual combination TOU C H ME D ICA L ME D IA