A highly sensitive pyrogen test for antibiotics I: detection of trace amounts of endotoxin in injectable sodium ampicillin preparations.

The rabbit pyrogen test (specified in the pharmacopeia) and the Limulus amebocyte lysate (LAL) test are influenced by high concentrations of certain antibiotics. Therefore, it has not been possible to detect trace amounts of endotoxin which may contaminate these antibiotics. To detect trace amounts of endotoxin in injectable sodium ampicillin, an ultrafiltration technique was utilized which removed the antibiotic and left a solution which contained predominantly the endotoxin. After ultrafiltration, a trace amount of pyrogen (which otherwise could not be detected) was found using both the rabbit pyrogen and the LAL tests. The endotoxin was also determined quantitatively using a chromogenic endotoxin reagent which is made by combining the Limulus amebocyte lysate and a synthetic substrate with a suitable chromophore.