Gram negative bacteria has an endotoxin in their cellular wall known as lipopolysaccharide. Endotoxin produce during multiplication or death of bacteria. Endotoxin is a stable molecule that are capable of resisting high temperature which make superamolecular aggregates in aqueous solution due to its amphipathic structure which makes depyrogenation more difficult than sterilization.
In pharmaceutical industry it is essential to remove endotoxin (depyrogenation) from parenteral since they have multiple harmful biological inflammatory activities in a human body including : pyrogenicity, lethality, macrophages activity etc.
Endotoxin removed by steam heat treatment (autoclaving) at 121˚C for 20 minute or dry heat treatment (hot air oven) for at least 1hr at 180˚C /250˚C for more than 30 min. It is well accepted that dry heat sterilization is efficient in destroying endotoxin. In the production of parenterals,it is necessary to both depyrogenate the final product and carry out steam heat sterilization to avoid bacterial contamination.