We would like to mention here 2 interesting articles from Brandon J.Thomas  and Gonçalo Farias  published in 2021: both articles are related to nasal suspension sprays and the characterization of particle size of active pharmaceutical ingredients (APIs) using the morphologically-directed Raman spectroscopy (MDRS) method. Both the API and excipient particles being present in the final dosage form, the analysis of nasal sprays with traditional particle sizing technologies do not allow to distinguish the chemical identity of the particles. MDRS technique allows ‘ingredient specific’ particle sizing and can be used for Bioequivalence (BE) assessment of suspension-based nasal products, this approach has been approved by FDA for use in lieu of a comparative clinical endpoint bioequivalence study already in 2016 . Brandon J.Thomas et al.  describe the use of dissolution as an orthogonal technique to confirm the trends observed with MDRS.
Discover in the video how we proceed in Alfatestlab to characterize nasal sprays APIs with the use of MSRD:
 Analytical method development for characterizing ingredient-specific particle size distributions of nasal spray suspension products – Brandon J.Thomas et al. J Pharm Sci. 2021 Jul;110(7):2778-2788.
 A Systematic Approach in the Development of the Morphologically-Directed Raman Spectroscopy Methodology for Characterizing Nasal Suspension Drug Products – Gonçalo Farias et al. AAPS J. 2021 May 18;23(4):73.