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Dry Powder Inhalers and the Risk of Error

The marketed DPIs show different resistances to inspiration, and there is an awareness that high resistance can generate high turbulence but at the same time it can make breathing through the device more difficult. The best solution would be to minimize the flow rate needed to completely empty the reservoir of the drug by means of an appropriate design of the flow pathway. In general, the pulmonary deposition of a drug in dry powder form is primarily dependent on the drug formulation (or drug/carrier formulation) and the inhaler design. Thus, if the pulmonary efficiency is compromised, it will be likely difficult for a patient to generate a sufficient flow rate to achieve complete inhalation of the drug. The different manufacturers of current DPIs therefore create devices with performance variations in relation to the inhalation flow rate needed for each of them to finely disperse the dose of the drug released to the patient [8] . In fact, the inspiratory flow rate required and the particle deaggregation are specific characteristics of each device and strictly dependent on physicochemical properties of the drug such as size distribution, morphology and particle density [9] . Most portable DPIs rely solely on the strength of the inhalation to entrain, aerosolize and deliver the powder to the patient’s lungs. Thus, their mechanism of action is also their Achilles’ heel: by making delivery dependent on inhalation flow, performance becomes a function of the strength of the patient’s inhalation. If the patient’s breathing is severely impaired, or in the case of a child with a low peak inspiratory flow rate, it is possible that not enough energy is available to entrain the powder. In a DPI, powder entrainment energy is a function of the quantity of air that the patient draws through the device In this issue of Respiration , Wieshammer and Dreyhaupt [1] highlight the importance of training in inhalational technique, particularly with dry powder inhalers (DPIs), as observed in our clinical practice. Deposition of the inhaled aerosol from DPIs is influenced by both the patient and the physical properties of the aerosol cloud [2, 3] . A substantial proportion of patients handled their inhalers poorly, and we need to be aware of the fact that the risk of error is high when DPIs are used and that the goal still remains the delivery of precise and uniform drug doses and increasing the respirable fraction in relation to the dose emitted from the device. DPIs, even if they provide the significant advantage of being breath actuated, need further technological development in order to release, independently of the patient’s inspiratory flow rates, definite and uniform drug doses with a high percentage of respirable particles [4] . In addition to the formulative aspects, it is of crucial importance for the therapeutic success of DPI that the device is capable of generating enough air flow to adequately aerosolize the dose, and with a sufficiently high respirable fraction. It has been demonstrated that a flow rate better than the maximum inspiratory peak is the relevant parameter for the performance of the device [5, 6] . Only those devices which require a limited inhalatory effort from the patient in order to reach an efficient flow rate can be considered as comfortable devices in terms of use. It has been determined that this effort should not exceed 50% of maximum effort [7] . It would also be beneficial to have a device with a low dependence on the inspiratory flow rate since it would render the application quite independent of the inhalation conditions.