Adequate delivery of drug to target sites within the lung is one of the most important factors concerning successful asthma management. Therefore the characteristics of inhalation devices as well as compliance of patients with the treatment regimen determine disease control.
First of all considerable differences exist regarding lung deposition achieved with certain kind of devices. Usually the amount of particles reaching the target site ranges from 8 to 60% with metered dose inhalers (pMDI) and from about 10 to over 40% with dry powder inhalers (DPI).
Lung deposition again is dependent on particle size and inhalation manoeuvre. In MDIs the fine particle fraction is high and variability in particle size low, while in DPIs these parameters are dependent on inspiratory flow rates generated through the device. However MDIs require a good coordination between dose activation and inhalation to ensure deposition of drug in the bronchial tree which is not the case with breath-actuated devices like DPIs.
Another factor influencing asthma control concerns the reassurance and education of patients in the process of repeated application. This is best achieved by control and feedback mechanisms implemented in the device itself. Dose counters for example help patients and professionals to assess whether medication was taken or not. Feedback mechanisms after each successful inhalation ensure the patient that sufficient drug hast been released, thus educating the patient in correct inhalation technique and also increasing compliance with treatment regimens.