We improved the Limulus amebocyte lysate (LAL) test for endotoxins in parenteral drugs using immobilized histidine and a filtration plate. In order to deal with many samples at the same time and to apply to a routine assay, we used a filtration plate having 96 wells instead of a filter unit with a working volume of 2 ml. LAL test-affecting substances which are contained in a parenteral drug were separated from endotoxins by adsorbing endotoxins on immobilized histidine in the well of a filtration plate. Then the adsorbed endotoxins were allowed to react with LAL reagent in the same well. We defined that this method had the higher precision than conventional methods and was not influenced by the concentrations of endotoxin and parenteral drugs. Hence we examined the recovery of endotoxin spiked to 23 kinds of parenteral drugs by this method, as a result, 100±25% of recovery was obtained from 17 kinds of them.
