depyrogenation

Depyrogenation is the process of removing pyrogens, particularly endotoxins, from materials intended for medical, pharmaceutical, and laboratory use. Pyrogens are fever-inducing substances produced by bacteria; endotoxins, lipopolysaccharides from Gram-negative bacteria, are among the most persistent and heat-stable pyrogens. Because endotoxins can remain in solutions or on surfaces after standard sterilization, depyrogenation aims to reduce their activity to regulatory limits to prevent febrile or inflammatory reactions in patients.

Endotoxins are unusually resistant to many routine sterilization methods, so depyrogenation relies on validated procedures that specifically target these molecules. The most common method is dry heat depyrogenation, typically using high-temperature dry air around 250°C for a defined period, applied to materials that can tolerate the heat. Other approaches include chemical depyrogenation with alkaline cleaners or oxidizing agents to degrade endotoxins, followed by thorough rinsing. Steam-based depyrogenation in specialized equipment is used for certain metal components. For liquids and water systems, depyrogenation may involve distillation, specialized filtration, or other processes designed to remove endotoxins to regulatory limits.

Testing for endotoxins is essential to verify depyrogenation effectiveness. The Limulus Amebocyte Lysate (LAL) assay and recombinant factor C assays are commonly used to measure endotoxin levels in finished products and on equipment. Regulatory guidance from pharmacopeias and authorities defines acceptable endotoxin limits, expressed as endotoxin units per milliliter or per device, depending on the product.