Maximum Valid Dilution (MVD) is the highest allowable dilution of a sample where a test method can still detect bacterial endotoxins at the required product limit.
For example, an MVD of 100 means the sample can be diluted up to 1:100. Diluting beyond this value may reduce the endotoxin concentration below the detection capability of the test and could result in an invalid assessment.
MVD is especially useful when a product contains substances that interfere with the LAL or recombinant factor C-based endotoxin test. Dilution can help reduce such interference, but the dilution must remain within the calculated MVD.
๐๐ก๐ฒ ๐๐ฌ ๐๐๐ ๐๐ฆ๐ฉ๐จ๐ซ๐ญ๐๐ง๐ญ?
Some pharmaceutical formulations can interfere with endotoxin detection by causing:
- ๐๐ง๐ก๐ข๐๐ข๐ญ๐ข๐จ๐ง: reducing the response generated by endotoxin.
- ๐๐ง๐ก๐๐ง๐๐๐ฆ๐๐ง๐ญ: increasing the response generated by endotoxin.
- ๐๐๐ญ๐ซ๐ข๐ฑ ๐ข๐ง๐ญ๐๐ซ๐๐๐ซ๐๐ง๐๐: caused by formulation components, viscosity, pH, salts, or other substances.
Dilution can reduce these effects and help establish suitable testing conditions. However, excessive dilution may make the endotoxin concentration too low to detect. MVD establishes the upper limit for dilution.
๐๐ก๐ ๐๐๐ฅ๐๐ฎ๐ฅ๐๐ญ๐ข๐จ๐ง ๐
๐จ๐ซ๐ฆ๐ฎ๐ฅ๐
Where:
- ๐๐ง๐๐จ๐ญ๐จ๐ฑ๐ข๐ง ๐๐ข๐ฆ๐ข๐ญ (๐๐): The maximum permissible endotoxin concentration for the product.
- ๐๐จ๐ง๐๐๐ง๐ญ๐ซ๐๐ญ๐ข๐จ๐ง: The starting concentration of the active ingredient (e.g., in mg/mL, Units/mL, or 1 for liquid solutions).
- ฮป (๐๐๐ฆ๐๐๐): The labelled sensitivity of the lysate or the lowest point on the assay’s standard curve (EU/mL).
๐๐จ๐ฐ ๐๐๐ ๐๐ฌ ๐๐ฌ๐๐ ๐ข๐ง ๐๐๐
A typical approach is:
๐๐ซ๐จ๐๐ฎ๐๐ญ โ ๐๐๐ญ๐๐ซ๐ฆ๐ข๐ง๐ ๐๐ง๐๐จ๐ญ๐จ๐ฑ๐ข๐ง ๐๐ข๐ฆ๐ข๐ญ โ ๐๐๐ฅ๐๐ฎ๐ฅ๐๐ญ๐ ๐๐๐ โ ๐๐๐ซ๐๐จ๐ซ๐ฆ ๐๐ข๐ฅ๐ฎ๐ญ๐ข๐จ๐ง/๐ข๐ง๐ญ๐๐ซ๐๐๐ซ๐๐ง๐๐ ๐ฌ๐ญ๐ฎ๐๐ฒ โ ๐๐๐ฅ๐๐๐ญ ๐ฌ๐ฎ๐ข๐ญ๐๐๐ฅ๐ ๐๐ข๐ฅ๐ฎ๐ญ๐ข๐จ๐ง โ ๐๐๐ซ๐๐จ๐ซ๐ฆ ๐๐๐
The laboratory may evaluate several dilutions below the MVD to identify a dilution that minimizes product interference while maintaining reliable endotoxin detection.
The selected dilution should also satisfy the applicable method-specific acceptance criteria. For example, studies may assess spike recovery to demonstrate that the chosen dilution does not produce significant inhibition or enhancement.
