Table 3.

Technical advancement levels of the mechanisms providing feedback to the patient on the use of the inhaler and the correctness of the inhalation carried out in currently used multi-dose DPIs [32–39]

Technical advancement levels	Description
Level I – basic system	Visual or auditory information (signal) that a single dose of medication has been dispensed and the presence of a dose counter (present in all II Generation DPIs), e.g. Turbuhaler®
Level II – advanced system	Visual and/or auditory and/or gustatory information (signal) confirming that a dose of medication has been inhaled. The gustatory signal applies to virtually all DPIs except for Turbuhaler® (the lactose dose is too low), e.g. Easyhaler®
Level III – highly advanced system	Visual and/or auditory information (signal) informing the patient that at least the minimum inspiratory flow has been achieved, increasing the likelihood of inhaling the desired (SmPC-compliant) aerosol cloud of drug. Some II Generation DPIs, such as NEXThaler®, are equipped with these systems
Level IV – digital technology	DPIs including an electronic module (fixed or attached to the inhaler). Basic digital DPIs – record only the use of DPI, and advanced digital DPIs – additional measuring of PIF, time to reach PIF, inspiratory volume, inspiratory time, e.g. Digihaler®