Liquid chromatographic methods for separation, determination, and bioassay of enantiomers of etodolac: A review

The control of enantiomeric purity and determination of individual enantiomeric drug molecules remains the subject of importance for clinical, analytical, and regulatory purposes and to facilitate an accurate evaluation of the risks posed by them to human health. A large number of pharmaceuticals are marketed and administered as racemates. Etodolac is among such nonsteroidal anti‐inflammatory drugs. Overall literature reports on its enantioseparation are scanty. Liquid chromatography (LC) methods of enantioseparation of (±)‐etodolac, including certain unconventional ones, are well covered and discussed in this paper. Methods of direct approach without using chiral columns or chiral thin‐layer chromatography plate and of indirect approach using certain chiral derivatizing agents such as ( S )‐naproxen and ( S )‐levofloxacin are described. Most interesting aspects include establishment of structure and molecular asymmetry of chemically different types of diastereomeric derivatives using liquid chromatography with mass spectrometry (LC–MS), 1 H NMR spectroscopy and by drawing conformations in three dimensional views by using certain software. The methods provide chirality recognition even in the absence of pure enantiomers. Besides, recovery of pure enantiomers by detagging or via solubility difference of chiral inducing reagent and the analyte, without racemization at any stage, has been achieved. The limits of detection and quantification are much lower than the industry benchmarks.