Pyrogens and Filtration

George Younan
ProcessHQ, Inc.

A great deal of attention is paid to the sterility of products and processes in pharmaceutical systems. The degree of sterility is referred to as bioburden or level of living organisms present. Although traditional methods of sterilization are very effective in ensuring the elimination of bioburden often they are ineffective in the elimination of pyrogens and endotoxins. In fact, the eradication process itself may add to the generation of pyrogens and endotoxins. Recent advancements in filtration technology have yielded media that is significantly more effective in the exclusion of pyrogens and endotoxins from process fluids and gases.

Pyrogens or endotoxins in their most common form are lipopolysacharides that come from the cell walls of gram-negative bacteria, this type of bacteria often contaminates ultra-pure water. Lipopolysacharides are generally not susceptible to the low temperature heat (121 degrees C) of most sterilization methods. Moist heat sterilization procedures often do little to eliminate these toxins and in fact cause the release of endotoxins when the bacteria burst during the sterilization. Although high temperature dry heat is effective, it is often not an acceptable method for sterilization. The high temperatures necessary with the use of depyrogenation systems (>250 degrees C) is often not compatible with many of the materials or methodologies used in pharmaceutical processing. Additionally one cannot dry heat sanitize water, which is often the source of these contaminants. Water for injection systems (due to the moist heat nature of their sanitization process) may actually maintain levels of pyrogenicity. The use of water for injection in the manufacture of process buffers and fluids, or the rinsing of cleaned materials with high purity water, may in fact contaminate these materials.

The general implementation of good aseptic procedures to minimize the bacterial contamination of critical components and systems will undoubtedly reduce the presence of endotoxins and pyrogens. Additionally recent advances in filtration have allowed the development of media that has proven to be significantly more effective in the removal of these toxins. Hollow micro fiber extrusion has allowed for the development of filtration media that has retention rates of 0.05 microns absolute. At a .05 micron pore size some cartridges have shown 100% pyrogen removal at 5 eu/ml challenge levels. Additionally the use of positively charged membrane media has been effective since bacterial endotoxin is characteristically negatively charged and thus electrostatically attracted to the filter. The implementation of appropriate exclusion media is important in the assurance of low endotoxin levels. The use of the above types of filters in the final filtration of process fluids or in the manufacture of ultra-pure water seems to be an effective method for the removal of pyrogens and endotoxins.