Development of an in vitro Endotoxin Test for Monoolein–Water Liquid Crystalline Gel for Use as an Implant

Purpose: Drugs that are administered by parenteral route must be apyrogenic. The aim of this study was to develop an in vitro endotoxin test for liquid crystalline gels for use as implants, using a monoolein–water liquid crystalline gel as a model.
Methods: The gel-clot technique was used. The gel was dissolved first in isopropyl myristate, and the endotoxins were extracted with water for bacterial endotoxin test. Tests for the labelled lysate sensitivity and interfering factors were performed to validate the developed method. The limit of detection of endotoxin in the gel was also determined.
Results: The labelled lysate sensitivity was confirmed. It was not influenced by the presence of extracts from the gels. Endotoxins in the contaminated test gels were completely extracted. Endotoxin concentration in the tested gels was below the calculated threshold endotoxin level.
Conclusion: A method to perform in vitro endotoxins test of liquid crystalline gels was successfully developed and validated. Application of the technique to gels currently being developed in our laboratories indicate that the gels were apyrogenic.

Keywords
In vitro bacterial endotoxin test; liquid crystalline gels; test validation; monoolein–water.