Application Note: Particle Characterization Of Dry Powder Inhalers

DPIs are an alternative to the aerosol based inhalers commonly called metered-dose inhaler (or MDI). The DPIs may require some procedure to allow a measured dose of powder to be ready for the patient to take. The medication is commonly held either in a capsule for manual loading or a proprietary form from inside the inhaler. Once loaded or actuated, the operator puts the mouthpiece of the inhaler into their mouth and takes a deep inhalation, holding their breath for 5-10 seconds. There are a variety of such devices including the Inhalator, Spinhaler, Rotahaler, Turbuhaler, Accuhaler, the Diskus, and others. The dose that can be delivered is typically less than a few tens of milligrams in a single breath.

Dry powder inhalers (DPIs) are devices that deliver medications to the lungs to treat respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD). Although the compendial tests1 for DPIs are based on cascade impactors, microscopic analysis provides useful information on both particle size and shape distributions of the powder products. Automated image analysis now facilitates quantitative particle size and shape distribution data that can prove valuable to both formulators and quality control efforts.