Thimerosal was developed and registered under the trade name Merthiolate in 1929 by the Indianapolis-based pharmaceutical company, Eli Lilly, and marketed as an antibacterial and antifungal agent. It has been used as an additive to prevent bacterial contamination in vaccines and other compounds such as immune globulin preparations, skin test antigens, anti-venins, ophthalmic and nasal products, and tattoo inks.

The chemical formula for thimerosal is C₉H₉HgNaO₂S. In the body it is metabolized to ethylmercury (C₂H₅Hg⁺) and thiosalicylate. Thimerosal causes susceptible bacteria to autolyze (break down their own cells with self-produced enzymes) via an unknown mechanism.

Material Safety Data Sheet

See Full Material Safety Data Sheet

Synonyms: ethyl-2-mercaptobenzoato(2-)-O,S--mercurate sodium, mercury((o-carboxyphenyl)thio)ethyl sodium salt, mercurothiolate, merzonin sodium, SET, sodium ethylmercuric thiosalicylate, sodium merthiolate, thimerosalate, thiomersalate, merfamin, merthiolate, merthiolate sodium, merzonin, nosemack, merseptyl, 2-mercaptobenzoic acid mercury complex, elcide 75, thiomersal, ethylmercurithiosalicylic acid sodium salt, various other systematic and non-systematic names.

Usage

Drug, anti-infective, anti-bacterial, anti-fungal, preservative.

Physical data

Appearance: white or slightly yellow powder

Molecular formula: C₉H₉HgNaO₂S
Molar Mass: 404.81 g/mol
CAS No: 54-64-8
EC No: 200-210-4
EC index number: 080-004-00-7
HS Code: 2930 90 70
Storage class (VCI): 6.1 B (Non-flammable toxic materials)
Packing-category: G
WGK: 3 (highly polluting substance)
R Phrase: R 26/27/28-33-50/53
S Phrase: S 13-28.1-36-45-60-61
pH value: ∼6.7 (10 g/l, H₂O, 20 °C)
Melting point: 232 - 233 °C (decomposition)
Bulk density: 500 kg/m³
Solubility in water: 1000 g/l (20 °C)

Stability

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

Toxicology

Poison. Experimental neoplastigen and teratogen. Harmful by inhalation and ingestion. May cause reproductive damage. May be harmful through skin contact. Typical OEL 0.05 mg/m3.

Chemical Hazard Symbol: T+ = Very toxic Criteria: Inhalation, swallowing, or absorption through the skin in very small amounts can cause considerable damage to health, and may sometimes be lethal. In the event of exposure serious evidence of severe, possibly irreversible damage to health by single, repeated, or prolonged absorption. MSDS Hazard Symbol T+

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Children 'at risk' as parents delay jab
From Evening Standard (London), 8/18/04 by REBECCA SMITH

PARENTS are boycotting existing vaccinations until they can get the new five-in-one jab for their children next month.

Some are waiting a month or more for the new mercury-free injection, despite warnings from government experts that doing so could put their children at risk of contracting potentially fatal diseases.

The new jab protects against polio, diphtheria, tetanus, whooping cough and Hib (a range of bacterial infections including meningitis). It replaces the current live oral polio vaccine, and will be given to babies aged between two and four months.

The new single jab, marketed as Pediacel, will be available from 27 September. The polio vaccine will not be live and the compound does not contain the mercury- based preservative thiomersal, which some parents fear is linked to autism.

The Government denies the change of vaccine is an admission mercury is unsafe. Dr David Salisbury, head of the immunisation programme, said the reason for removing thiomersal was because the new polio vaccine would not be effective if that preservative was used with it.

There is also widespread agreement that exposure to mercury should be limited where possible.

Sara Richards, of the Royal College of Nursing's practice nurses' association, said: " Parents are already refusing the old vaccine until the new one becomes available."

She said RCN members had told her parents feared the old vaccine would cause autism.

But Dr Salisbury warned that delaying vaccination could be dangerous.

"It is unfortunate some parents are reportedly delaying vaccination, as they are putting their children at risk of serious diseases," he said.

Kate Howie, a member of the practice nurses' association, said most parents were still happy with the old four-in-one vaccine but some were turning it down and preferring to wait for the new one.

She said: "We have been noticing that there have been a lot of parents coming in to practice in the last week and saying they would rather wait than have the old vaccine.

"It is up to us to ensure parents have as much information as possible so they feel confident that the four-in-one is safe to give their child, but we also have to respect the wishes of those who want to wait.

We are explaining that the children are slightly more at risk in the meantime."

Diphtheria, tetanus, whooping cough, Hib and polio can all be fatal.

About one in 500 children under 12 months with whooping cough dies. The risk is higher for the youngest babies.

The new five-in-one vaccine replaces the live polio virus, which carries a small risk of developingthe disease from the jab, with the dead virus and exchanges the whooping cough element for a version with fewer side-effects.

The new controversy follows the refusal of some parents to have children vaccinated with the measles, mumps and rubella (MMR) jab amid fears it could cause autism.

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