Current Edition

The Great Why Questions About Dry Powder Inhalers

The research pertains to the economic burden of asthma and chronic obstructive pulmonary disease and the impact of poor inhalation techniques with commonly prescribed dry powder inhalers as illustrated in three European countries. Currently, the direct cost burden of managing asthma and COPD for people using DPIs is €813 million, €560 million, and €774 million in Spain, Sweden, and the UK, respectively. Poor inhalation techniques comprised 2.2– 7.7% of direct costs, totalling €105 million in these three countries alone. When lost productivity costs were included, total expenditure increased to €1.4 billion, €1.7 billion, and €3.3 billion in Spain, Sweden, and the UK, respectively, with €782 million attributable to poor inhalation technique across the three countries.1,2

Airflow resistance

A major issue is current airflow resistance: “Current guidance is in line with these observations, suggesting that passive DPIs are all flow-rate dependent and that young children and elderly patients are at risk of not being able to achieve the flow rates necessary to effectively disperse the powder. The underlying factors controlling inspiratory pressures, flow rates and dispensing, and dispersion characteristics of the various DPIs explain why this is the case. While it is also clear then that some patients at the extremes of the population, with poor muscle strength, may not be able to achieve the inspiratory flow rates to utilise a given DPI”.3 “In particular, the inspiratory airflow generated by the patient represents the only active force (a passive force for the device) able to produce the micro-dispersion (even if differently sized for each device) of the powdered drug to inhale. On the other hand, the extent of the patient’s inspiratory airflow depends on the patient’s airway and lung conditions, and, partially, on the intrinsic resistive regimen of the device”. “While low resistance DPIs are still regarded as the easiest and the most comfortable devices for the patient, they instead require a high inhalation airflow rate to the patient, not always achievable. The reason is that the role of the other possible force involved in drug deagglomeration”.4


De-agglomeration is a major parameter in DPI design. “Dry powders designed for inhalation are very fine and can easily form agglomeration due to cohesion between individual particles and are hard to aerosolize. Despite the inhaler and formulation designs, patients are required to generate a forceful and deep inhalation through the DPI to de-agglomerate the powder formulation into respirable particles (with an aerodynamic size ? 5 µm) for efficient delivery to the lungs”.5