How are endotoxin limits calculated? How do my endotoxin test results relate to those limits?
Endotoxin limits for drug products specify the amount of endotoxin that can safely be present. Limits are based on human tolerance and generally specified in the USP monograph or if no monograph exists, calculated via USP <85> Bacterial Endotoxin Test. The testing limit calculation considers:
- Route of administration
- Dose of the product per kilogram of body weight (which should include the maximum bolus dose and the minimum patient weight)
- Duration (time) of administration
Once a limit is determined, USP <85> allows a testing facility flexibility to determine the appropriate test dilution to reduce drug sample properties that interfere with the test. Using the endotoxin limit and the assay's sensitivity, a maximum valid dilution (MVD) is calculated. The MVD provides the maximum dilution possible to obtain a result and maintain the sensitivity necessary to determine a pass or fail. For example, if a sample is submitted with an endotoxin test limit of NMT 14 EU/mL and the MVD is determined to be 1400, then the product concentration can be diluted no further than 1:1400 and still generate a result with the appropriate sensitivity.
The test result is calculated by the assay software using the test dilution and assay sensitivity. In a case where no endotoxins are present, for example, a 1:1000 dilution was used and no presence of endotoxin was detected, a result of <10 EU/mL is reported. A result which includes a "less than" value does not indicate that the actual endotoxin value is near the number reported, only that the dilution factor used allowed for that level of sensitivity in results calculation. This means that results of <10 EU/mL and <4 EU/mL both show no presence of endotoxin at the dilution with which they were tested; and neither result offers any indication of the exact level of endotoxin present below the values reported.
If you would like to always receive the same result when endotoxins are not detected, a validation of the endotoxin test method is required.
Contact ARL at email@example.com or 800-393-1595 to schedule your endotoxin test method validation.