Chemistry:Thiomersal

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Short description: Organomercury antiseptic and antifungal agent
Thiomersal
Thiomersal
Thiomersal-from-xtal-3D-balls.png
Names
IUPAC name
Ethyl(2-mercaptobenzoato-(2-)-O,S) mercurate(1-) sodium
Other names
Mercury((o-carboxyphenyl)thio)ethyl sodium salt, sodium ethylmercurithiosalicylate
Identifiers
3D model (JSmol)
8169555
ChEBI
ChEMBL
ChemSpider
DrugBank
EC Number
  • 200-210-4
1677155
KEGG
RTECS number
  • OV8400000
UNII
Properties
C9H9HgNaO2S
Molar mass 404.81 g/mol
Appearance White or slightly yellow powder
Density 2.508 g/cm3[1]
Melting point 232 to 233 °C (450 to 451 °F; 505 to 506 K) (decomposition)
1000 g/L (20 °C)
Pharmacology
1=ATC code }} D08AK06 (WHO)
Hazards
Safety data sheet External MSDS
GHS pictograms GHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard
GHS Signal word Danger
H300, H310, H330, H373, H410
P260, P273, P280, P301, P310, P330, P302, P352, P304, P340[2]
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no codeNFPA 704 four-colored diamond
1
3
1
Flash point 250 °C (482 °F; 523 K)
Lethal dose or concentration (LD, LC):
75 mg/kg (oral, rat)[3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☑Y verify (what is ☑Y☒N ?)
Infobox references

Thiomersal (INN), or thimerosal (USAN, JAN), also sold under the name merthiolate[4] is an organomercury compound. It is a well-established antiseptic and antifungal agent.[5]

The pharmaceutical corporation Eli Lilly and Company named it Merthiolate. It has been used as a preservative in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic and nasal products, and tattoo inks.[6] In spite of the scientific consensus that fears about its safety are unsubstantiated,[7][8][9][10] its use as a vaccine preservative has been called into question by anti-vaccination groups. A statement issued by the American Academy of Pediatrics and the US Public Health Service in 1999 prompted the removal of thimerosal from many vaccines.[11][12] It remains in use as a preservative for annual flu vaccines.[13]

History

Morris Kharasch, a chemist then at the University of Maryland filed a patent application for thiomersal in 1927;[14] Eli Lilly later marketed the compound under the trade name Merthiolate.[15] In vitro tests conducted by Lilly investigators H. M. Powell and W. A. Jamieson found that it was forty to fifty times as effective as phenol against Staphylococcus aureus.[15] It was used to kill bacteria and prevent contamination in antiseptic ointments, creams, jellies, and sprays used by consumers and in hospitals, including nasal sprays, eye drops, contact lens solutions, immunoglobulins, and vaccines. Thiomersal was used as a preservative (bactericide) so that multidose vials of vaccines could be used instead of single-dose vials, which are more expensive. By 1938, Lilly's assistant director of research listed thiomersal as one of the five most important drugs ever developed by the company.[15]

Structure

Thiomersal features mercury(II) with a coordination number 2, i.e. two ligands are attached to Hg, the thiolate and the ethyl group. The carboxylate group confers solubility in water. Like other two-coordinate Hg(II) compounds, the coordination geometry of Hg is linear, with a 180° S-Hg-C angle. Typically, organomercury thiolate compounds are prepared from organomercury chlorides.[1]

Uses

Antiseptic/antifungal

Thiomersal's main use is as an antiseptic and antifungal agent, due to its oligodynamic effect. In multidose injectable drug delivery systems, it prevents serious adverse effects such as the Staphylococcus infection that, in one 1928 incident, killed 12 of 21 children vaccinated with a diphtheria vaccine that lacked a preservative.[16] Unlike other preservatives at the time, such as phenol and cresol, thiomersal does not reduce the potency of the vaccines that it protects.[15] Bacteriostatics such as thiomersal are not needed in single-dose injectables.[17]

In the United States, the European Union, and a few other affluent countries, thiomersal is no longer used as a preservative in routine childhood vaccination schedules.[12] In the U.S., all vaccines routinely recommended for children 6 years of age and younger are available in formulations that do not contain thimerosal. Two vaccines (a TD and the single-dose version of the trivalent influenza vaccine Fluvirin) that may contain a trace of thiomersal from steps in manufacture, but less than 1 microgram of mercury per dose.[16] The multi-dose versions of some trivalent and quadrivalent influenza vaccines can contain up to 25 micrograms of mercury per dose from thiomersal. Also, four rarely used treatments for pit viper, coral snake, and black widow venom contain thiomersal.[18]

Outside North America and Europe, many vaccines contain thiomersal; the World Health Organization reported no evidence of toxicity from thiomersal in vaccines and no reason on safety grounds to change to more expensive single-dose administration.[19] The United Nations Environment Program backed away from an earlier proposal of putting thiomersal on the list of banned vaccine compounds as part of its campaign to reduce mercury exposure.[20] It stated that eliminating it in multi-dose vaccines, primarily used in developing countries, would lead to high cost and a refrigeration requirement that developing countries could ill afford. At the Minamata Convention on Mercury in 2013 thiomersal was excluded from the treaty.[21]

Toxicology

General toxicity

Thiomersal is very toxic by inhalation, ingestion, and in contact with skin (EC hazard symbol T+), with a danger of cumulative effects. It is also very toxic to aquatic organisms and may cause long-term adverse effects in aquatic environments (EC hazard symbol N).[22]

In the body, it is metabolized or degraded to ethylmercury (C2H5Hg+) and thiosalicylate.[16]

Cases have been reported of severe mercury poisoning by accidental exposure or attempted suicide, with some fatalities.[23] Animal experiments suggest that thiomersal rapidly dissociates to release ethylmercury after injection; that mercury's disposition patterns are similar to those after exposure to equivalent doses of ethylmercury chloride; and that the central nervous system and the kidneys are targets. Loss of motor coordination is a common sign. Similar signs and symptoms have been observed in accidental human poisonings. The mechanisms of toxic action are unknown.[23]

Fecal excretion accounts for most of the elimination from the body. Ethylmercury clears from blood with a half-life of about 18 days in adults by breakdown into other chemicals, including inorganic mercury.[24] The half-life of ethylmercury in the brains of infant monkeys is 14 days.[25] Risk assessment for effects on the nervous system have been made by extrapolating from dose-response relationships for methylmercury.[25] Methylmercury and ethylmercury distribute to all body tissues, crossing the blood–brain barrier and the placental barrier, and ethylmercury also moves freely throughout the body.[26]

Concerns based on extrapolations from methylmercury caused thiomersal to be removed from U.S. childhood vaccines, starting in 1999. Later it was reported that ethylmercury is eliminated from the body and the brain significantly faster than methylmercury, so the late-1990s risk assessments turned out to be overly conservative.[25] Though inorganic mercury metabolized from ethylmercury has a much longer half-life in the brain, at least 120 days, it appears to be much less toxic than the inorganic mercury produced from mercury vapor, for reasons not yet understood.[25]

As an allergen

Patch test

Thiomersal is used in patch testing for people who have dermatitis, conjunctivitis, and other potentially allergic reactions. A 2007 study in Norway found that 1.9% of adults had a positive patch test reaction to thiomersal;[27] a higher prevalence of contact allergy (up to 6.6%) was observed in German populations.[28] Thiomersal-sensitive individuals can receive intramuscular rather than subcutaneous immunization,[29] though there have been no large sample sized studies regarding this matter to date. In real-world practice on vaccination of adult populations, contact allergy does not seem to elicit clinical reaction.[28]

Thiomersal allergy has decreased in Denmark, probably because of its exclusion from vaccines there.[30] In a recent study of Polish children and adolescents with chronic/recurrent eczema, positive reactions to thiomersal were found in 11.7% of children (7–8 y.o.) and 37.6% of adolescents (16–17 y.o.). This difference in the sensitization rates can be explained by changing exposure patterns: The adolescents received six thiomersal-preserved vaccines during their life course, with the last immunization taking place 2–3 years before the study. Younger children received only four thiomersal-preserved vaccines, with the last one applied five years before the study, while further immunizations were performed with thiomersal-free vaccines.[31]

Disproven autism hypothesis

Main page: Unsolved:Thiomersal and vaccines

Following a review of mercury-containing food and drugs mandated in 1999, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics asked vaccine manufacturers to remove thiomersal from vaccines as a purely precautionary measure, and it was rapidly phased out of most U.S. and European vaccines.[15][32] Some parents saw the action to remove thiomersal—in the setting of a perceived increasing rate of autism as well as increasing number of vaccines in the childhood vaccination schedule—as indicating that the preservative was the cause of autism.[15] The scientific consensus is that no evidence supports these claims, while the rate of autism continued to climb in children who did not take the thiomersal-preserved childhood vaccines.[9][33][34][35]

Scientific and medical bodies such as the Institute of Medicine[35] and World Health Organization,[36][37] as well as governmental agencies such as the Food and Drug Administration[16] and the CDC[38] reject any role for thiomersal in autism or other neurodevelopmental disorders.[39] Unconvinced parents attempted to treat their autistic children with unproven and possibly dangerous treatments, and refused to vaccinate them due to fears about thiomersal toxicity.[40] Studying thiomersal potentially diverts resources away from research into more promising areas for autism.[41] Thousands of lawsuits have been filed in U.S. federal court to seek damages from allegedly toxic vaccines, including those purportedly caused by thiomersal.[42]

See also

References

  1. ↑ 1.0 1.1 Melnick, J. G.; Yurkerwich, K.; Buccella, D.; Sattler, W.; Parkin, G. (2008). "Molecular Structures of Thimerosal (Merthiolate) and Other Arylthiolate Mercury Alkyl Compounds". Inorg. Chem. 47 (14): 6421–26. doi:10.1021/ic8005426. PMID 18533648. 
  2. ↑ "Thimerosal T5125". https://www.sigmaaldrich.com/catalog/product/sigma/t5125?lang=en&region=US. 
  3. ↑ Chambers, Michael. "ChemIDplus – 54-64-8 – RTKIYNMVFMVABJ-UHFFFAOYSA-L – Thimerosal [USP:JAN – Similar structures search, synonyms, formulas, resource links, and other chemical information."]. https://chem.nlm.nih.gov/chemidplus/rn/54-64-8. 
  4. ↑ "Merthiolate poisoning: MedlinePlus Medical Encyclopedia" (in en). https://medlineplus.gov/ency/article/002678.htm. 
  5. ↑ "Thimerosal and Vaccines | Vaccine Safety | CDC" (in en-us). 2020-08-25. https://www.cdc.gov/vaccinesafety/concerns/thimerosal/index.html. 
  6. ↑ Sharpe, M. A.; Livingston, A. D.; Baskin, D. S. (2012). "Thimerosal-Derived Ethylmercury is a Mitochondrial Toxin in Human Astrocytes: Possible Role of Fenton Chemistry in the Oxidation and Breakage of mtDNA". Journal of Toxicology 2012: 1–12. doi:10.1155/2012/373678. PMID 22811707. ""...widely used in medical products, including as a preservative in vaccines, immunoglobulin preparations, skin test antigens, antivenins, ophthalmic and nasal products, and tattoo inks..."". 
  7. ↑ Immunization Safety Review Committee, Board on Health Promotion and Disease Prevention, Institute of Medicine (2004). Immunization Safety Review: Vaccines and Autism. Washington, DC: The National Academies Press. ISBN 978-0-309-09237-1. 
  8. ↑ Doja, Asif; Roberts, Wendy (November 2006). "Immunizations and autism: a review of the literature". Can J Neurol Sci 33 (4): 341–46. doi:10.1017/s031716710000528x. PMID 17168158. 
  9. ↑ 9.0 9.1 "Vaccines Do Not Cause Autism". https://www.cdc.gov/vaccinesafety/concerns/autism.html. 
  10. ↑ Gołoś, A; Lutyńska, A (2015). "Thiomersal-containing vaccines - a review of the current state of knowledge". Przeglad Epidemiologiczny 69 (1): 59–64, 157–61. PMID 25862449. 
  11. ↑ Hurley, A; Tadrous, M; Miller, E (July–September 2010). "Thimerosal-Containing Vaccines and Autism: A Review of Recent Epidemiologic Studies". J Pediatr Pharmacol Ther 15 (3): 173–181. PMID 22477809. 
  12. ↑ 12.0 12.1 Bigham, M; Copes, R (2005). "Thiomersal in vaccines: balancing the risk of adverse effects with the risk of vaccine-preventable disease". Drug Saf 28 (2): 89–101. doi:10.2165/00002018-200528020-00001. PMID 15691220. 
  13. ↑ "Not Immune" (in en-US). The New Yorker. 2015-02-08. https://www.newyorker.com/magazine/2015/02/16/immune-3. Retrieved 2022-10-02. 
  14. ↑ U.S. Patent 1,672,615 "Alkyl mercuric sulphur compound and process of producing it".
  15. ↑ 15.0 15.1 15.2 15.3 15.4 15.5 Baker, JP (2008). "Mercury, Vaccines, and Autism: One Controversy, Three Histories". Am J Public Health 98 (2): 244–53. doi:10.2105/AJPH.2007.113159. PMID 18172138. 
  16. ↑ 16.0 16.1 16.2 16.3 "Thimerosal and vaccines" (in en). Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. 2018-01-02. https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/thimerosal-and-vaccines. 
  17. ↑ "Thimerosal in Vaccines: Frequently Asked Questions". Food and Drug Administration. https://www.fda.gov/cber/vaccine/thimfaq.htm. 
  18. ↑ "Mercury in plasma-derived products". U.S. Food and Drug Administration. September 9, 2004. https://www.fda.gov/cber/blood/mercplasma.htm. 
  19. ↑ Global Advisory Committee on Vaccine Safety (July 14, 2006). "Thiomersal and vaccines". World Health Organization. https://www.who.int/vaccine_safety/topics/thiomersal/en/index.html. 
  20. ↑ Hamilton, Jon (17 December 2012). "Doctors Argue Against Proposed Ban on Vaccine Preservative". NPR. https://www.npr.org/blogs/health/2012/12/17/167280941/experts-argue-against-proposed-ban-on-vaccine-preservative. 
  21. ↑ Sulaski Wyckoff, Alyson (January 22, 2013). "Global ban on mercury grants exception to thimerosal-containing vaccines". AAP News (American Academy of Pediatrics). https://www.aappublications.org/content/early/2013/01/22/aapnews.20130122-1. Retrieved August 24, 2019. 
  22. ↑ "Safety data sheet, Thiomersal Ph Eur, BP, USP". Merck. June 12, 2005. http://www.merck-chemicals.com/documents/sds/emd/int/en/8170/817043.pdf. 
  23. ↑ 23.0 23.1 Clarkson, TW (2002). "The three modern faces of mercury". Environ Health Perspect 110 (S1): 11–23. doi:10.1289/ehp.02110s111. PMID 11834460. PMC 1241144. http://www.ehponline.org/members/2002/suppl-1/11-23clarkson/clarkson-full.html. 
  24. ↑ Magos, L. (2003). "Neurotoxic character of thimerosal and the allometric extrapolation of adult clearance half-time to infants". Journal of Applied Toxicology 23 (4): 263–269. doi:10.1002/jat.918. PMID 12884410. https://pubmed.ncbi.nlm.nih.gov/12884410/. Retrieved 2021-01-19. 
  25. ↑ 25.0 25.1 25.2 25.3 Clarkson, TW; Magos, L (2006). "The toxicology of mercury and its chemical compounds". Crit Rev Toxicol 36 (8): 609–62. doi:10.1080/10408440600845619. PMID 16973445. 
  26. ↑ Clarkson, TW; Vyas, JB; Ballatori, N (2007). "Mechanisms of mercury disposition in the body". Am J Ind Med 50 (10): 757–64. doi:10.1002/ajim.20476. PMID 17477364. 
  27. ↑ Dotterud, LK; Smith-Sivertsen, T (2007). "Allergic contact sensitization in the general adult population: a population-based study from Northern Norway". Contact Dermatitis 56 (1): 10–15. doi:10.1111/j.1600-0536.2007.00980.x. PMID 17177703. 
  28. ↑ 28.0 28.1 Uter, W; Ludwig, A; Balda, BR (2004). "The prevalence of contact allergy differed between population-based and clinic-based data". J Clin Epidemiol 57 (6): 627–32. doi:10.1016/j.jclinepi.2003.04.002. PMID 15246132. 
  29. ↑ Aberer, W (1991). "Vaccination despite thimerosal sensitivity". Contact Dermatitis 24 (1): 6–10. doi:10.1111/j.1600-0536.1991.tb01621.x. PMID 2044374. 
  30. ↑ Thyssen, JP; Linneberg, A; Menné, T; Johansen, JD (2007). "The epidemiology of contact allergy in the general population – prevalence and main findings". Contact Dermatitis 57 (5): 287–99. doi:10.1111/j.1600-0536.2007.01220.x. PMID 17937743. 
  31. ↑ Czarnobilska, E; Obtulowicz, K; Dyga, W; Spiewak, R (2011). "The most important contact sensitizers in Polish children and adolescents with atopy and chronic recurrent eczema as detected with the extended European Baseline Series". Pediatr Allergy Immunol 22 (2): 252–56. doi:10.1111/j.1399-3038.2010.01075.x. PMID 20969635. 
  32. ↑ "Thimerosal in vaccines: frequently asked questions (FAQs)". Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. June 7, 2007. https://www.fda.gov/cber/vaccine/thimfaq.htm. 
  33. ↑ DeStefano, F (2007). "Vaccines and autism: evidence does not support a causal association". Clin Pharmacol Ther 82 (6): 756–59. doi:10.1038/sj.clpt.6100407. PMID 17928818. 
  34. ↑ Doja, A; Roberts, W (2006). "Immunizations and autism: a review of the literature". Can J Neurol Sci 33 (4): 341–46. doi:10.1017/s031716710000528x. PMID 17168158. 
  35. ↑ 35.0 35.1 Immunization Safety Review Committee, Board on Health Promotion and Disease Prevention, Institute of Medicine (2004). Immunization Safety Review: Vaccines and Autism. Washington, DC: The National Academies Press. ISBN 978-0-309-09237-1. http://www.nap.edu/catalog/10997.html. 
  36. ↑ World Health Organization (2006). "Thiomersal and vaccines: questions and answers". http://who.int/vaccine_safety/topics/thiomersal/questions/en/. 
  37. ↑ WHO. "Statement on thiomersal". https://www.who.int/vaccine_safety/committee/topics/thiomersal/statement_jul2006/en. 
  38. ↑ Centers for Disease Control (February 8, 2008). "Mercury and vaccines (thimerosal)". https://www.cdc.gov/vaccinesafety/updates/thimerosal.htm. 
  39. ↑ Sugarman, SD (2007). "Cases in vaccine court – legal battles over vaccines and autism". N Engl J Med 357 (13): 1275–77. doi:10.1056/NEJMp078168. PMID 17898095. http://content.nejm.org/cgi/content/full/357/13/1275. 
  40. ↑ Harris, G; O'Connor, A (June 25, 2005). "On autism's cause, it's parents vs. research". New York Times. https://www.nytimes.com/2005/06/25/science/on-autisms-cause-its-parents-vs-research.html. 
  41. ↑ Offit, PA (2007). "Thimerosal and vaccines – a cautionary tale". N Engl J Med 357 (13): 1278–79. doi:10.1056/NEJMp078187. PMID 17898096. http://content.nejm.org/cgi/content/full/357/13/1278. 
  42. ↑ Autism cases in vaccine court:



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