Clinical comparisons of inhaler systems: what are the important aspects?

Inhaled medications are the mainstay of asthma treatment. This not only provides the greatest clinical effect in asthmatic patients, but does so with the least systemic side effects. A wide variety of inhaler systems exist, each of which has inherent advantages and disadvantages. These have to be considered when making a choice of inhaler system for a specific clinical circumstance, as no currently available system is ideal in every clinical situation. Three main types of inhaler systems currently exist and, of these, the pressurized metered dose inhalers (pMDIs) and dry powder inhalers (DPIs) are most frequently used. The advantages of pMDIs are their portability, ease of use (in a properly instructed and adequately co-ordinated patient), cheap cost of manufacture, and low inspiratory flow rates needed to achieve adequate drug deposition in the lung. The main disadvantages of pMDIs, such as oropharyngeal deposition of drug and improper use (in an uncoordinated patient), can be minimized by the use of a spacer device. In contrast, DPIs are easy to use (no co-ordination between actuation and inhalation is required by the patient) and portable, and for the DPI, Turbuhaler, are multiple dose and deposit twice the dose of drug in the lung in comparison with pMDIs. Moreover, the side effects, namely bronchoconstriction and cough, associated with the use of pMDIs are minimized or eliminated with the use of Turbuhaler. A potential disadvantage of DPI systems is that patients need to generate inspiratory flow rates of at least 30 L/min to obtain optimal drug delivery. This is, however, feasible in almost all patients, even in those patients with very severe airflow obstruction.