Evaluation of a Chromogenic Procedure for Use with the Limulus Lysate Assay of Bacterial Endotoxins in Drug Products

Abstract

Some factors affecting the use of a chromogenic substrate with Limulus lysate for assaying bacterial endotoxins in certain drug products were evaluated. The study was involved with determining whether ingredients in any of 12 different drug products interfered with the LAL reaction as measured spectrophotometrically with the chromogenic substrate as compared to visually using the gel-clot procedure. All reagents were obtained from a single manufacturer. Seven products (naloxone HCI, saline, mannitol, promethazine HCI, chlorpromazine HCI, gentamicin sulfate, non-B-vitamin complex) were compatible for analysis by both the gel-clot and chromogenic method. Because of its color a B-complex vitamin sample had too high of a background absorbance and interfered with the chromogenic assay. Three products (edetate disodium, diphenhydramine HCl, fluorescein sodium) could not be analyzed by either method. Although temperature and time requirements are more exacting with the chromogenic method, it is a less time consuming assay and somewhat simpler to perform than the gel-clot method.