Pyrogen

Overview
The word pyrogen, which can be traced to the Greek pyro, meaning burning or fire and gennao, meaning to make or to create, is now used as an apt description for substance that produce elevated body temperature. Pyrogens are usually bacterial products and remains or decaying products of the bacterial cell walls. Even in minimum dose, these substances induce elevated body temperature when injected into humans and animals. Pyrogens are usually high-molecular-weight substances of polymerous nature, like lipopolysacharids. Pyrogens could be either microbial or non-microbial.

Endotoxins

Endotoxins are high-molecular-weight complexes associated with the outer membrane of gram-negative bacteria (GNB). They are the most usual cause of the elevated body temperature, induced by contaminated drug products. Their pyrogenic activity is higher than that of other pyrogenic substances. It could be said that the absence of such bacterial endotoxins in a drug implies the absence of pyrogenic components in examined drug in general. Endotoxins are similar to lipopolysacharids, they are heat stable and can survive the sterilisation process. In their molecular structure, endotoxins contain lipid A which is responsible for the endotoxic activity of the endotoxins. The free form of lipid A, extracted from endotoxins by acid hydrolysis, has almost the same spectrum of biological activities as the endotoxin itself.

Reference: BLECHOVA1 & PIVODOVA ACTA VET. BRNO 2001, 70: 291–296 {http://vfu-www.vfu.cz/acta-vet/vol70/pdf/70_291.pdf}