Endotoxin is an essential lipopolysacchride (LPS) component of the cell wall of Gram-negative bacteria which elicits a pyrogenic response when injected into the human bloodstream. They are also toxic to cells grown in tissue culture conditions. When the bacterial cell dies, the membrane of the cell ruptures and endotoxins are released into the surrounding environment. This can cause contamination that may have adverse effects on a variety of applications and experiments. Endotoxins can be found in the air, water, soil, via human contact, and any non-sterile environment. Since siRNA are used in some in vivo study, testing your product lines for this common contaminant will add integrity to your products.
 
The FDA has set the following maximum permissible endotoxin levels for drugs distributed in the United States:
Drug (injectable, Intrathecal) - 0.2 EU/kg product
Drug (injectable, non-intrathecal) - 5 EU/kg product
Sterile water - 0.25-0.5 EU/ml (depends on intended use

As part of the QC of this siRNA, an endotoxin test is carried out by an external laboratory using a validated assay. The amount of sample required for the kinetic turbidometric method is 20 mg. Our clients have set an upper limit for endotoxins of ≤ 2 EU/mg and the actual values we obtain lie mostly in the range from 0.01 to 0.1, sometimes even lower.