What Is Endotoxin? Why It Matters in Injectable Peptides
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Endotoxin

Also called bacterial endotoxin, LPS, lipopolysaccharide, LAL test, EU/mg · Reviewed

Definition: Endotoxin is a substance from the outer wall of certain bacteria (gram-negative bacteria), released when they die. Injected in high amounts it can cause fever, severe inflammation, septic shock and death (FDA). It is measured in endotoxin units (EU) and is a separate problem from live germs: a vial can be sterile and still carry endotoxin.

How it is measured

The standard test is the Limulus amebocyte lysate (LAL) test. FDA has accepted LAL testing in place of the older rabbit fever test for more than 30 years.

USP chapter <85> sets the limit for injected drugs with a formula, K/M. K is the most endotoxin a person can get per kg of body weight per hour without a meaningful fever: 5 EU/kg for most injections. M is the largest dose given within one hour.

The upper limit for a 70 kg adult

  1. K = 5 EU per kg per hour.
  2. 5 EU/kg x 70 kg = 350 EU within one hour.
  3. FDA calls these values the upper limit for injectable products, so stricter limits may be set.

Why sterile is not enough

Killing bacteria does not remove endotoxin; their dead walls still carry it. In one study of semaglutide vials bought online, no live germs grew from the powder, but endotoxin was found in all three samples, at 2.16 to 8.95 EU per mg (Ashraf 2024).

An endotoxin result also only means something with its unit and the lot it came from. A COA that lists sterility but no endotoxin result has not answered this question.

Why it matters when you track doses

Fever, chills or a strong reaction soon after a shot are reasons to contact a doctor. Logging the vial and lot with each dose, and the injection site, helps you and your doctor tell a site problem from a vial problem.

Read more on Dose Track: Bacteriostatic vs sterile water

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
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Frequently asked questions

Is endotoxin the same as an infection?+
No. An infection is live germs growing. Endotoxin is a substance from bacteria walls that can cause a reaction even when no live bacteria are present.
What does EU/mg mean?+
Endotoxin units per milligram of product. Multiply by the amount injected to get the endotoxin in a dose.
If a vial is sterile, is it endotoxin free?+
Not necessarily. Endotoxin comes from bacteria walls and stays after the bacteria die, so sterility and endotoxin are tested separately.

Sources

  1. FDA draft guidance: Setting Endotoxin Limits During Development of Investigational Oncology Drugs and Biological Products (July 2020), section III
  2. FDA guidance: Pyrogen and Endotoxins Testing, Questions and Answers (Edition 2)
  3. Ashraf et al. J Med Internet Res 2024 (semaglutide vials bought online without a prescription: LC-MS, sterility and endotoxin tests). PMID 39509151

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