The application of ultrasonics in the assessment of the in vitro dissolution rate of powders

The application of ultrasonics in assessing a dissolution test with improved discriminating ability towards micronised powders is proposed and promising results are reported. The case study described refers to two batches of a poorly soluble model drug, aceclofenac; the known and measurable differences in the dimensional characteristics of the powdered samples, particle size and specific surface area, were not reflected in the in vitro dissolution rates assessed according to pharmacopoeial procedures. On the contrary, the test performed in a differently assembled apparatus enabling ultrasound application, allowed a clear distinction to be made between the dissolution profiles of the two batches, thus highlighting the direct relationship between dissolution rate and particle size. Ultrasonics seem to promote drug particle dispersion, which overcomes their tendency to agglomerate due to the increase in the specific surface area associated with particle size reduction.