Thiomersal

Thiomersal (INN), commonly known in the United States as thimerosal, (C9H9HgNaO2S) is a mercury-containing (approximately 49% mercury by weight) organic compound (organomercurial) used as an antiseptic and antifungal agent.

It was developed and registered under the trade name Merthiolate in 1929 by the pharmaceutical company Eli Lilly and Company, and has been used as a preservative in vaccines, immune globulin preparations, skin test antigens, antivenoms, ophthalmic and nasal products, and tattoo inks.

The compound is being phased out from most childhood vaccinations by packaging the vaccines in single-dose vials, which eliminates the need for bacteriostatics like thiomersal. A 2006 study shows downward trends in neurodevelopmental disorders following removal of Thiomersal from vaccines.

Stability


Stable. May degrade in sunlight. Incompatible with strong acids, strong bases, strong oxidizing agents, iodine, heavy metal salts.

Toxicology

Thiomersal is a very toxic compound which is harmful by inhalation and ingestion (hazard symbol T+). It is a neoplastigen and a teratogen. Thiomersal is also dangerous for the environment (hazard symbol N). For more safety information on how to handle thiomersal, consult an MSDS

Thiomersal causes susceptible bacteria to autolyze (break down their own cells with self-produced enzymes) via an unknown mechanism. In the body, it is metabolized to ethylmercury (C2H5Hg+) and thiosalicylate.

Most thiomersal containing vaccines contain no more than 25 micrograms of ethyl mercury. A can of tuna fish, by comparison, can contain up to 50 micrograms of methyl mercury.

History

Thiomersal was developed by Dr. Morris Kharasch, a chemist and Eli Lilly and Company fellow at the University of Maryland and then at the University of Chicago.

A patent for the alkyl mercuric sulfur compound, which was felt to have possibilities as an antiseptic and antibacterial product, was filed in the 1920s. Eli Lilly and Company registered the compound under the trade name Merthiolate in 1929. It was used to kill bacteria and prevent contamination in antiseptic ointments, creams, jellies, and sprays used by consumers and in hospitals. Thiomersal was used in eg. nasal sprays, eye drops, contact lens solutions, immunoglobulins, and vaccines.

Thiomersal was first put in vaccines in 1931 by Eli Lilly Corporation and used as a preservative (bactericide) in order that multi-dose vials of vaccines could be used instead of single dose vials, which were more expensive.

Today, discussions or descriptions of vaccines frequently include comments to the effect that the subject vaccine does not contain thimerosal as a preservative. It should be noted that this does not mean that the vaccine does not contain thimerosal. Many vaccines that do not contain thimerosal as a preservative do in fact contain thimerosal, and frequently the amount of thimerosal included in this way is labelled a "trace". Definitions for what "trace" actually means appears to vary - one common definition describes a "trace" amount as being 1 microgram of mercury per dose or less

The actual amount of thimerosal present in vaccines currently listed on the childhood vaccination schedule, whether trace or otherwise, varies from nil to 0.01%

Other products that may contain thimerosal include products derived from blood plasma such as Rho(D) Immune Globulin, pit viper antivenin and coral snake antivenin, as well as black widow spider antivenin

Timeline

Early-1930s- first added to vaccines as a bactericide.
Mid-1980s- used as a preservative in virtually all whole-cell DPT vaccines, which were routinely administered four times each to children before eighteen months of age, starting at two months.
Late 1980s- Hib vaccines are recommended for administration to children at eighteen months. They contain thiomersal.
Early 1990s- In the USA three doses of Hepatititis B vaccine (at that time containing Thiomersal) are recommended for infants under six months of age, beginning on the day of birth; four doses of Hib are recommended within an eighteen month period, beginning at age two.
Late 1990s- three of the vaccines included in Vaccination schedules for children between six and eighteen months of age contain thiomersal.
1999- The American Academy of paediatrics requests removal of thiomersal from all paediatric vaccines.
2002- The USA Centers for Disease Control (CDC) and the USA Food and Drug Administration (FDA) state that: although thiomersal was to be discontinued in some paediatric vaccines, they would not be recalling any unused stocks, as there is no proof that low doses of thiomersal is dangerous, and that the change was purely cautionary.
2006- The World Health organisation, with US funding, is providing thiomersal-containing vaccines for children in developing countries with the same amounts of thiomersal as were given American children at their peak exposure levels. Current vaccination schedules give these in a shorter time period.
2006- In the latest review by the WHO committee (at its meeting of 6-7 June 2006) the conclusion previously reached was reaffirmed that there is no evidence of toxicity in infants, children or adults exposed to thiomersal in vaccines.
2006- A Spring 2006 study published in the Journal of American Physicians and Surgeons shows statistically significant downward trends in neurodevelopmental disorders following removal of Thiomersal from vaccines.

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