Endotoxin is the lipopolysaccharide (LPS) component of the outer cell wall of Gram-negative bacteria. When bacteria die or shed their cell wall, the lipopolysaccharide is released into the surrounding environment — including into pharmaceutical raw materials if those materials have been in contact with bacterial contamination during manufacture, packaging, or reconstitution.
Injected endotoxin causes a pyrogenic response: fever, chills, inflammation, and at higher doses septic-shock-like cardiovascular symptoms. Even low concentrations (sub-microgram in a typical injection) can cause measurable systemic reactions, which is why the regulatory limits are tight and the test is sensitive.
USP General Chapter <85> specifies the Limulus Amebocyte Lysate (LAL) assay as the reference method for bacterial endotoxin quantification in pharmaceutical raw materials and products. The assay uses an extract from the blood of the Atlantic horseshoe crab (Limulus polyphemus), which clots in the presence of bacterial endotoxin. The clotting rate is proportional to endotoxin concentration, and modern kinetic-chromogenic assays measure the rate to sub-picogram sensitivity.
USP <85> defines three valid methods:
We use the kinetic chromogenic method on a Charles River Endosafe platform because it is the most sensitive and the most repeatable for peptide / API matrices.
Endotoxin Units per milligram (EU/mg) is the standard reporting unit for bacterial endotoxin content per unit of test material. 1 EU is approximately 0.1-0.2 ng of endotoxin from the reference standard (EC-6 reference endotoxin). The result is reported as the mass concentration in the test material — for example, a value of 0.5 EU/mg means 0.5 endotoxin units per milligram of peptide.
The acceptance limit depends on the planned route of administration and dose. The standard formula is:
K / M
where K is the pyrogenic threshold (5 EU/kg for IV / subcutaneous routes, 0.2 EU/kg for intrathecal) and M is the maximum human dose in mg/kg. For a 70 kg adult receiving a 5 mg subcutaneous peptide dose, the calculation works out to roughly 70 EU/mg as the acceptance limit. The actual reported value should be well below that.
Maximum Valid Dilution (MVD) is the maximum dilution of the test sample at which the endotoxin limit can still be detected. The MVD calculation determines how dilute the sample can be before falling below the detection threshold. A well-prepared peptide solution at the appropriate concentration falls within the MVD, ensuring the endotoxin measurement is valid.
On a USP <85> COA, the MVD is reported alongside the observed result so the reviewer can confirm the test was performed within the valid dilution range.
Positive Product Control (PPC) is a spike of known endotoxin into the sample matrix. The recovery of the spike (between 50 % and 200 %) demonstrates that the sample matrix is not interfering with the LAL assay — i.e., it is not artificially suppressing or amplifying the apparent endotoxin response.
PPC spike recovery is mandatory under USP <85> for every sample. Peptides can sometimes interfere with the LAL reaction; the PPC catches this and signals that the result needs to be interpreted carefully.
An injectable-grade COA from us (or any USP <85>-aligned lab) should include:
USP <85> covers endotoxin specifically — the lipopolysaccharide from Gram-negative bacterial cell walls. It does not catch:
For a true injectable-grade COA, USP <85> should be paired with USP <71> sterility — both are included in our Full Disclosure panel on every peptide compound page.
USP <85> endotoxin testing is the regulatory line between research-use-only peptide powder and injectable-grade material. It uses the LAL assay to quantify bacterial endotoxin in EU/mg against an acceptance limit calculated from the intended dose and route. The COA should report the value, the limit, the MVD, the PPC spike recovery, the lambda correlation, and the analyst signature. If your peptide COA only reports a single endotoxin number without those metadata, it is hard to know whether the test was valid for your intended use.
See the LAL endotoxin assay on every Full Disclosure panel: Semaglutide, Tirzepatide, BPC-157, peptide testing overview.