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{{Short description|Removal of pyrogens from solutionsolutions}}
{{more footnotes|date=May 2012}}
<!-- Image with unknown copyright status removed: [[Image:Endo1.jpeg|right]] -->
'''Depyrogenation''' refers to the removal of pyrogens[[pyrogen (fever)|pyrogen]]s from [[solution (chemistry)|solution]]s, most commonly from injectable pharmaceuticals.
 
A [[wikt:pyrogen|pyrogen]] is defined as any substance that can cause a fever. Bacterial pyrogens include [[endotoxins]] and [[exotoxins]], although many pyrogens are endogenous to the host. Endotoxins include [[lipopolysaccharide]] (LPS) molecules found as part of the cell wall of [[Gram-negative]] bacteria, and are released upon bacterial cell [[lysis]]. Endotoxins may become pyrogenic when released into the bloodstream or other tissue where they are not usually found. Although the colon contains Gram-negative bacteria in abundance, they do not cause a pyrogenic effect as the bacteria are not undergoing gross lysis, and the immune system is not exposed to free endotoxin while the colonic wall is intact.
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Because pyrogens are often difficult to remove, inactivation or destruction of the LPS molecule can sometimes be preferable.
 
;===Acid-base [[hydrolysis]] ===
{{main|Hydrolysis}}
<!-- Image with unknown copyright status removed: [[Image:Endo3.jpeg|right]] -->
:This method has been shown to cleave Lipid A from the polysaccharide in the LPS molecule (see right). The [[lipid]] moiety alone is not soluble in water. Thus unable to bind to [[endothelial]] cells, it is rendered inactive. However, acid-base hydrolysis can denature a target protein, and is thus unsuitable when purifying a protein.
 
;[[===Oxidation]]===
:Oxidation using hydrogen peroxide is often used as a low cost pyrogen destroying solution. The mechanism for this destruction is unknown, but hydrogen peroxide can easily be removed further downstream in the purification process, and is therefore a useful method of pyrogen removal. However, like acid-base hydrolysis, it is not suitable when purifying proteins.
{{main|Oxidation}}
;Heating▼
:HeatingOxidation methodsusing arehydrogen peroxide is often used toas ensurea thatlow glasscost andpyrogen otherdestroying labsolution. equipmentThe aremechanism freefor ofthis pyrogenic material. Heatdestruction is appliedunknown, bybut bakinghydrogen inperoxide acan dryeasily heatbe ovenremoved thatfurther isdownstream designed specifically forin the depyrogenationpurification process. Although endotoxins are relatively thermally stable, sufficientand heatingis (250&nbsp;°C for 30 min) results intherefore a [[Loguseful reduction|3-log reduction]]method of endotoxinpyrogen levelsremoval. DueHowever, tolike theacid-base high temperature levelshydrolysis, this methodit is also not suitable when purifying proteins.
▲;===Heating===
;Sodium Hydroxide
Heating methods are often used to ensure that glass and other lab equipment are free of pyrogenic material. Heat is applied by baking in a dry heat oven that is designed specifically for the depyrogenation process. Although endotoxins are relatively thermally stable, sufficient heating (250&nbsp;°C for 30 min) results in a [[Log reduction|3-log reduction]] of endotoxin levels. Due to the high temperature levels, this method is also not suitable when purifying proteins.
:When purifying proteins, sodium hydroxide (NaOH) can be used safely and effectively. It is also widely used for depyrogenation of non-autoclavable equipment (e.g. plastics) and chromatography columns. In fact, when using an anion exchanger to remove pyrogens, it is necessary to clean the column with NaOH after each batch.▼
 
===Alkalies===
{{main|Alkali}}
▲:When purifying proteins, alkalies such as sodium hydroxide (NaOH) can be used safely and effectively. It is also widely used for depyrogenation of non-autoclavable equipment (e.g. plastics) and chromatography columns. In fact, when using an anion exchanger to remove pyrogens, it is necessary to clean the column with NaOH after each batch.
 
== Preventive methods ==
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== References ==
{{Reflist}}
* Sofer, G.; Hagel, L. (1997). Handbook of Process Chromatography: A guide to Optimization, Scale-up, and Validation. Academic Press, 158-161. {{ISBN|0-12-654266-X}}▼
* Tours, N. and Sandle, T. Comparison of dry-heat depyrogenation using three different types of Gram-negative bacterial endotoxin, European Journal of Parenteral and Pharmaceutical Sciences, Volume 13, No.1, 2008, pp17–20pp. 17–20▼
 
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*[http://www.acciusa.com/bet/update/index.html LAL Update]
*[http://www.acciusa.com/pdfs/newsletter/LAL_Vol.11No.5.pdf.html Depyrogenation LAL Update]
* [https://www.fda.gov/ICECI/Inspections/InspectionGuides/InspectionTechnicalGuides/ucm072918.htm FDA Office of Regulatory Affairs: Inspection Technical Guide, Bacterial Endotoxins/Pyrogens]▼
▲* Sofer, G.; Hagel, L. (1997). Handbook of Process Chromatography: A guide to Optimization, Scale-up, and Validation. Academic Press, 158-161. {{ISBN|0-12-654266-X}}
* [http://textbookofbacteriology.net/endotoxin.html Textbook of Bacteriology]▼
▲* [https://www.fda.gov/ICECI/Inspections/InspectionGuides/InspectionTechnicalGuides/ucm072918.htm FDA Office of Regulatory Affairs: Inspection Technical Guide, Bacterial Endotoxins/Pyrogens]
* [http://www.horseshoecrab.org/med/med.html Horseshoe Crab Medical Uses]▼
▲* [http://textbookofbacteriology.net/endotoxin.html Textbook of Bacteriology]
*[https://www.researchgate.net/publication/282704534_A_Practical_Approach_to_Depyrogenation_Studies_Using_Bacterial_Endotoxin A Practical Approach to Depyrogenation Studies Using Bacterial Endotoxin]
▲* [http://www.horseshoecrab.org/med/med.html Horseshoe Crab Medical Uses]
▲* Tours, N. and Sandle, T. Comparison of dry-heat depyrogenation using three different types of Gram-negative bacterial endotoxin, European Journal of Parenteral and Pharmaceutical Sciences, Volume 13, No.1, 2008, pp17–20
* A Practical Approach to Depyrogenation Studies Using Bacterial Endotoxin [https://www.researchgate.net/publication/282704534_A_Practical_Approach_to_Depyrogenation_Studies_Using_Bacterial_Endotoxin]
 
[[Category:Toxicology]]
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