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Microscopic View Is a Term Acceptable to the Food and Drug Administration to Describe Using Bright-Field Optical Microscopy to Determine Globule Size or Polarized Light Microscopy for Determining Drug Particle Size for Multi-Phasic Semisolid Products. Microscopic View Testing Is Recommended When Globule Size or Drug Particle Size Is a Q3 Critical Quality Attribute of the Drug Product.
https://www.fda.gov/downloads/drugs/newsevents/ucm591915.pdf

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• TITLE: Characterization of a Liquid Crystal Stabilized Pharmaceutical Oil-in-Water Emulsion Optimized for Skin Delivery

  AUTHORS: Melinda J. Sutton, David W. Osborne, Kevin Dahl, Victoria Bax, G. Alan Schick

  KEYWORDS: Pharmaceutical Emulsion, Skin Delivery, Liquid Crystal Stabilized Emulsion, Polarized Light Microscopy, Topical Formulation

  JOURNAL NAME: Journal of Cosmetics, Dermatological Sciences and Applications, Vol.8 No.4, November 16, 2018

  ABSTRACT: A moisturizing cream containing 25 wt% of an organic solvent, diethylene glycol monoethyl ether (DEGEE), is observed to be stabilized by an emulsifying wax blend of cetearyl alcohol, dicetyl phosphate, and ceteth-10 phosphate (tradename Crodafos CES). Polarized light microscopy indicates that the Crodafos CES helps to produce a liquid-crystal stabilized oil-in-water emulsion, which is physically stable for months under accelerated aging conditions and chemically stable over the full topical pH range of 3.5 to 9. Emulsion globule size in the cream is observed to be dependent on the degree of emulsifying wax neutralization, with the globule size decreasing with increasing cream pH. The superior solubilizing properties of DEGEE combined with the full pH range and liquid-crystal stabilizing properties of the Crodafos CES give this formulation the potential for a wide range of applications in the topical delivery of active pharmaceutical ingredients.