ABSTRACT
Recent history of dry powder inhalation dates back to the sixties of the previous century. The design and development of dry powder inhalers (DPIs) in this period was driven by patient dissatisfaction with metered dose inhaler (MDI) use and the imminent ban of chlorofluorocarbon propellants in these MDIs. For their design, the 1960s state of the art in powder formulation for low dose drugs (adhesive mixtures) was used and powder masses with single drug doses were measured into hard gelatin capsules. Adhesive mixtures and capsule inhalers are not the most optimal combination, however, because of the high flow rates needed to empty the capsule completely. Capsule DPIs also lack an efficient powder dispersion principle and as a result relatively coarse aerosols are delivered to the respiratory tract at high velocities. This causes considerable drug deposition in the mouth and throat region. This unsatisfactory performance has given dry powder inhalation science a boost, resulting in the development of multi-dose DPIs and an excess of studies into the mechanisms and variables involved in adhesive mixture preparation and dispersion. Also, various particle engineering techniques have been explored and are currently used to improve drug aerosolisation by controlling the interparticulate forces in the powders for inhalation. Thus, increased understanding of powder dispersion and particle deposition in the respiratory tract and improved technology for drug formulation and aerosol delivery have opened the way to new, mostly high dose applications for dry powder inhalation, like vaccines, inhaled antibiotics, and systemically acting drugs.
