Particle Size

Particle size is one test that the FDA requires for API (Active Pharmaceutical Ingredients), especially if this is in a solid oral dosage form. The particle size will affect the release properties of the drug from the product, since the surface area to volume of the particle will change in relation to the particle size. This may also be considered critical for true solutions, such as injectables, as the process may be affected by how fast the API particles dissolve in the solvent. There are a variety of techniques for measuring particle size, some of which are microscopic analysis, laser-light scattering (often using a Malvern particle sizer) of either dry powder or a liquid suspension, and light obscuration. The results are a statistical measure and are often reported as the particles size of 10%, 50%, and 90% of the particles to indicate the size distribution.

Particle sizing is dependent on not only the specific technique that is used to measure the particles, but also on the specific method used with that technique. Therefore, a specification must be developed using data from the technique and method that will be used to control particle size. If the particle size can be related to the rate of dissolution of the API, product, or API in the process, this will be strong supportive data for the specification.
Short courses in particle size analysis and dissolution testing are available from the American Chemical Society (www.chemistry.org) and the American Association of Pharmaceutical Scientists (http://www.aapspharmaceutica.com/).



Mark A. Schreiber, Ph.D.
http://www.linkedin.com/in/maschreiber