Most of the inhalation products in the market use metered dose inhaler (MDI) technology or dry powder inhaler (DPI) technology. MDIs use propellant to deliver desired dose of liquid formulation in aerosol form. DPI contains active in fine particulate form embedded onto an inert carrier. In both cases, amount of drug dispensed from the device reaching the lungs is dependent upon drug product characteristics as well as formulation-device relationship. Hence, in addition to particle size, aerodynamic distribution of the drug upon delivery by the device plays an important role in determining amount of drug reaching the lungs. Therefore particle size characterization is an important tool in determining the extent of drug delivery from the metered dose inhaler. Aerodynamic particle size distribution is frequently determined by use of cascade impactors and data so generated is accepted by regulatory agencies as a tool for predicting efficacy of MDIs and DPIs. This review discusses principle and working of cascade impactors. Additionally, the review also examines the role of laser diffraction technique in estimating size of dispersed particles.
Factors Influencing Aerodynamic Particle Size Distribution of Suspension Pressurized Metered Dose Inhalers
