Usage Examples
- The batch passed sterility but the endotoxin testing result was out of specification, so the lot stays on hold.
- We cannot move endotoxin testing to recombinant Factor C on the licensed product until the supplement is approved.
- Endotoxin testing on the water for injection loop is the first record QA asks for when a lot fails.
What is Endotoxin Testing?
Endotoxin testing is the quality control assay that quantifies bacterial lipopolysaccharide in parenteral drugs, biologics, and blood-contacting devices, detecting one specific fever-causing contaminant rather than all pyrogens or viable microorganisms.
Endotoxin testing exists because sterilization does not solve the pyrogen problem. Lipopolysaccharide from the outer membrane of Gram-negative bacteria is heat-stable and survives autoclaving, filtration, and the death of the organism that produced it. Injected, it triggers fever, hypotension, and at sufficient dose septic shock. Killing the bacteria is therefore not evidence that the solution is safe to inject.
Endotoxin testing covers what is injected or contacts blood: parenteral drug products, biologics, water for injection, container-closure components, and blood-contacting devices. Endotoxin testing does not cover oral solids or topicals, and it does not detect viable organisms, non-endotoxin pyrogens from Gram-positive bacteria, or fungal and viral pyrogens. A clean endotoxin result says nothing about sterility.
Endotoxin testing is run against a compendial chapter, USP General Chapter 85 or Ph. Eur. 2.6.14, using a lysate-based or recombinant assay qualified for the specific product matrix. Endotoxin testing results appear as a line in the drug product or device release specification, and for licensed biologics the method itself is locked into the approved application rather than left to the laboratory.
Not to be confused with
- Sterility testing
- sterility testing looks for viable organisms; endotoxin testing measures a heat-stable cell-wall fragment that persists after those organisms are killed. A batch can pass sterility and fail endotoxin.
- Pyrogen testing
- the rabbit pyrogen test responds to any substance that raises body temperature; endotoxin testing quantifies bacterial lipopolysaccharide only. Non-endotoxin pyrogens clear an endotoxin test undetected.
- Bioburden testing
- bioburden counts the viable organisms present before sterilization to size the sterilization challenge; endotoxin testing quantifies a contaminant molecule and is indifferent to whether the organisms are alive.
- Depyrogenation
- depyrogenation is the process step, typically dry heat or rinsing, that removes or inactivates endotoxin; endotoxin testing is the measurement that demonstrates the step worked.
Endotoxin and pyrogen obligations sit inside the CGMP and biologics regulations rather than in one dedicated part.
What you must do
- 1Perform appropriate laboratory testing on each batch of drug product that purports to be sterile and/or pyrogen-free, and keep the test procedures in writing and follow them (QA owns the procedure, QC executes)21 CFR 211.167(a)
- 2Test each lot of final containers of any licensed biological product intended for use by injection for pyrogenic substances, unless the product falls in an exempted class21 CFR 610.13(b)
- 3Before substituting a different endotoxin or pyrogen method for a licensed biologic, submit evidence in a license application or supplement showing the modification provides assurances of safety, purity, potency, and effectiveness equal to or greater than the specified method21 CFR 610.9(a)
- 4Obtain written approval of that method change from the Director of CBER or CDER before using the new method for lot release21 CFR 610.9(b)
Common mistakes
Reading a sterility pass as an endotoxin pass
sterilization kills the organism and leaves its lipopolysaccharide behind, so a sterile solution can still be pyrogenic. 21 CFR 211.167(a) names sterile and pyrogen-free as two separate claims, each requiring its own testing; conflating them puts a releasable-looking lot on the market with no data behind half of its label claim.
Switching the endotoxin method before the supplement clears
teams validate a recombinant assay, prove equivalence internally, and start releasing on it. For a licensed biologic that sequence is backwards: 21 CFR 610.9 requires both the filed evidence and written approval from the CBER or CDER Director, so every lot released on the unapproved method was released against a method the license does not authorize.
Testing only the finished product
endotoxin enters through water systems, glassware, and elastomeric components, not through the fill step. Teams that monitor the drug product alone get recurring out-of-specification results with no assignable cause, because the failing input, the water for injection loop or the depyrogenation cycle, is never in the data set.
When This Matters
- The batch passed sterility but the endotoxin testing result was out of specification, so the lot stays on hold.
- We cannot move endotoxin testing to recombinant Factor C on the licensed product until the supplement is approved.
- Endotoxin testing on the water for injection loop is the first record QA asks for when a lot fails.
Frequently Asked Questions
Endotoxin testing measures a contaminant molecule; sterility testing looks for living organisms. Autoclaving or filtration kills bacteria but leaves their lipopolysaccharide intact and pyrogenic, so a batch can pass sterility and still fail endotoxin. 21 CFR 211.167(a) treats sterile and pyrogen-free as separate claims, each needing its own laboratory testing.
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