When performing the Bacterial Endotoxin test, we observe changes within a solution that occur as a reaction to the presence of endotoxin. As such, it is necessary that the test medium be a liquid. For pharmaceutical products, the sample is typically already a liquid or is in a powder form which can be reconstituted for testing. However, when testing a medical device, we need to perform an extraction to analyze the presence of endotoxins.
Guidance on endotoxin tests on medical devices can be found in AAMI ST72, ISO11737-3 and USP <161>. Each of these standards offers the same general guidelines. The samples should be immersed in water that contains no detectable endotoxin at 37°C. Alternatives, however, are permitted if equivalency is demonstrated.
At Nelson Labs, various extraction methods are utilized depending on sample type and needs of the sponsor.
Per ST72 and ISO 11737-3, commonly the extraction is performed by immersion of the test article in water at an ambient temperature that is incubated for a minimum of 1 hour at 37°C with agitation.
USP 161 states: “The standard extraction method is to soak or immerse the device or flush the fluid pathway with extracting fluid that has been heated to 37 ± 1.0°, keeping the extracting fluid in contact with the relevant surface(s) for NLT 1 h at controlled room temperature. Alternate extraction or rinsing methods may be used, but must be demonstrated to be equivalent to or better”
It is acknowledged that no matter what extraction method is being performed, there will inherently be some inefficiency and all endotoxins present may not be represented in the sample extract. In order to account for this inefficiency of extraction more stringent limits are imposed on medical devices.
Endotoxins are challenging. Extract and extraction methods suffer from poor extraction efficiencies and reproducibility. This fact is recognized by AAMI ST72, stating that “investigations have demonstrated that the extraction of endotoxin from spiked device materials might not achieve complete recovery”. Therefor limits for medical devices are set much more stringent “to account for any possible inefficiency in the extraction method.”
Furthermore, in contrast to bioburden determination where often extraction of micro-organisms is required, when extracting endotoxins from a medical device, there is no requirement for performing efficiency testing.
