Impurities in drugs IV: Indomethacin

One lot of indomethacin raw material, five lots of capsule preparations, and three lots of supporitory formulations were screened for impurities by TLC. Only the suppository products exhibited impurities above trace levels. The two main impurities were present at levels estimated at approximately 0.5 and 2%. After isolation from preparative TLC plates, they were identified by NMR, IR, and mass spectroscopy as the alpha-substituted monoglyceryl esters of 4-chlorobenzoic acid and indomethacin, respectively.