What is an endotoxin?

Endotoxins are complex molecules composed of lipid A, core oligosaccharide, and O-antigen polysaccharide, primarily found in the outer membrane of Gram-negative bacteria such as Escherichia coli and Salmonella. Unlike exotoxins, endotoxins are not secreted but released upon bacterial cell lysis. They are highly stable, resistant to heat and many disinfectants, and can persist in aqueous environments.

Why are endotoxins a concern in biopharmaceuticals?

In therapeutic products, even trace amounts of endotoxin can induce fever, inflammation, septic shock, and other adverse immune reactions. Regulatory agencies such as the FDA, EMA, and MHRA require strict endotoxin testing for parenteral drugs, vaccines, and implantable medical devices. The standard test is the Limulus Amebocyte Lysate (LAL) assay, which detects endotoxins based on the clotting reaction of horseshoe crab blood cells. Alternative methods, such as recombinant Factor C (rFC), are emerging to reduce reliance on animal-derived reagents.

How are endotoxins controlled and tested?

Endotoxin control begins with raw material sourcing, cleanroom manufacturing, and validated sterilisation processes. Testing is performed using LAL or rFC assays, with limits defined in pharmacopoeias such as USP <85>, EP 2.6.14, and BP. The acceptable endotoxin level is typically expressed in endotoxin units (EU) per dose or per millilitre, with stringent thresholds for intravenous and intrathecal products.

Related concepts

Endotoxin testing is integral to compliance with ISO 10993-12 (biological evaluation of medical devices), GHS hazard classification, and REACH regulations. Endotoxin levels are also monitored in cell culture media and buffers used in biomanufacturing to ensure product safety and consistency.