Aerosol particle generation from dry powder inhalers: can they equal pressurized metered dose inhalers?

In comparison with pressurized metered dose inhalers (pMDIs), dry powder inhalers (DPIs) emit a semi-stable aerosol cloud and are inspiratory flow actuated and inspiratory flow driven. In vitro studies show that different DPIs vary in their efficiency as delivery systems of fine drug particles (aerodynamic diameter < 5 microns). The efficiency of DPIs may vary according to the inspiratory force used to generate the aerosol. In comparison with other DPIs, Turbuhaler has been shown to be an efficient fine particle generator at weak, moderate and strong inspiratory forces. Deposition studies using human throat casts have shown that the throat has a minor influence on the deposition of drugs delivered from DPIs, whereas the throat has a major influence on the deposition of drug delivered from pMDIs. The fine particle dose able to penetrate the human throat casts was considerably higher for budesonide Turbuhaler than for budesonide pMDI, whereas for fluticasone propionate the fine particle dose was considerably higher from the pMDI than from Diskhaler. Thus, whether the fine particle dose and the deposition pattern of a drug generated from DPIs can equal that generated from pMDIs depends on the drug, the formulation and the patient.