A drug product or medical device may be sterile, but it can still contain endotoxin that will make a patient sick. Endotoxin is a complex lipopolysaccharide (LPS) found in the outer cell membrane of gram-negative bacteria, typically water borne. Sterilizing by autoclave or other means may kill these bacteria but leave the endotoxin behind. Endotoxin is measured in Endotoxin Units per milliliter (EU/mL). One EU/mL equals approximately 0.1 to 0.2 ng/mL.
Endotoxin is quantified in drug products or medical devices using Limulus Ameobocyte Lysate (LAL) derived from the blood of horseshoe crabs. The presence of endotoxin mixed with LAL causes LAL to clot. When LAL is standardized, quantification is possible.
Kinetic assays are also available, that measure increase in reactant turbidity. These endotoxin tests require less dilutions and are preferred for quantification.
Only a few mL or gm of test product are required, and TAT is possible in 1 day if necessary.