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The airways of the lung are a series of bifurcating tubes which begin at the trachea, divide into the main bronchi, the conducting bronchioles and conclude in the terminal bronchioles and the alveoli (1). This complex anatomical structure, which varies across patient groups, makes reproducible administration of therapeutic agents via this route problematic, but as the airways of the lung provide a huge, accessible surface area, the pulmonary administration of many therapeutic agents is highly desirable.
The origin of inhaled therapies can be traced back 4,000 years to India, where people smoked the leaves of the Atropa belladonna plant to suppress coughs. This developed in the 19th and early 20th centuries to pretreated cigarettes that contained stramonium powder mixed with tobacco to treat the symptoms of asthma. A superficial view of the inhaled field today would suggest that we have come a long way from using combustion to deliver aerosols to the lung, but despite vast amounts of money spent on research and the availability of numerous new inhaled devices, we are still struggling to match the delivery efficiency, reproducibility and value for money that traditional combustible delivery systems achieved hundreds of years ago.
The role of the delivery device in facilitating emerging opportunities and resolving the issues associated with ‘problem compounds’, whether for local or systemic delivery, threatens to cloud this sector of the healthcare market with products which are over-engineered and over-priced. Although device design has undoubtedly had a positive impact on the field of inhaled delivery over the last 10 years in terms of patient acceptability and performance, the fundamentals of formulation development seemed to have been lost in a haze of high performance devices.
Upon their conception, nebulisers, metered dose inhalers (MDIs) and dry powder inhalers (DPIs) each had a niche in the clinician’s tool box when designing optimal therapy for a particular disease. In the near future, all three types of device will look very similar; they will all be portable and all attain relatively similar delivery efficiency (2-4). This has a number of benefits for both the patient and the clinician. However, the cost of these devices is extremely high, a consequence of the technology involved and the requirement to tailor the device specifically for the delivery of individual agents. More importantly, the pharmaceutical industry is more frequently using a high-technology device as a safety net to try and offset poor formulation design – a claim that can be directed at many devices that have been designed recently to administer macromolecules.
So what can be done to stop the costs of inhaled product development spiralling out of control? One suggestion is that we go ‘back to basics’ and use the wealth of new found scientific knowledge in the areas of device design and formulation analysis to produce a simple, effective formulation that can be manufactured using scalable equipment and administered in a robust manner using a low-cost device. If this vision can be realised, perhaps this route of delivery will finally prove to be a viable alternative to parenteral administration, and the patient’s quality of life can be improved in a cost-efficient manner through pulmonary delivery. |
