Abstract
Dilution of samples with water (water dilution) was not appropriate to measure the endotoxin activity in solutions containing chelating agents and detergents, typical formulations showing low endotoxin recovery (LER). Dilution of the samples with 2 mM magnesium solution (magnesium dilution) or addition of the samples directly to the Limulus amebocyte lysate (direct method) provided accurate endotoxin values in the samples. The difference between the water dilution and the magnesium dilution/the direct method seemed to be caused by endotoxin activity decrease during the water dilution. Endotoxin activity was maintained for more than a month in LER solutions at 4oC, when the activity was measured by the magnesium dilution or the direct method. The magnesium concentration in the diluent for the magnesium dilution should be greater than the concentration of the chelating agent in the sample. The magnesium dilution is the most appropriate dilution method for endotoxin measurement in LER solutions. Sodium citrate and polysorbate 20 showed stronger LER effects than phosphate buffer and polysorbate 80, respectively. Human serum albumin was also found to be an LER mitigating factor, and this suggested that protein might reduce LER effects.
- Bacterial Endotoxins Test
- Endotoxin
- Limulus amebocyte lysate
- Lipopolysaccharide
- Low endotoxin recovery (LER)
- Magnesium dilution method
- Received September 5, 2018.
- Accepted March 6, 2019.
- Copyright © 2019, Parenteral Drug Association
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