Thimerosal, or thiomersal, or merthiolate (sodiumethyl-mercurithiosalicylate) has been used as a preservative in vaccines and topical medication for years.
It is bacteriostatic against Gram+ and – bacteria, and active against fungi and yeast.
1 to 25% of positive patch-tests to thimerosal in patients with contact allergy.
10% of patients with positive patch-tests to thimerosal show adverse reactions to thimerosal containing vaccines.
Young adults (greater exposure to vaccines containing thimerosal?)
Possible sources of thimerosal (0.001 to 0.1%).
- Vaccines: diphtheria, tetanus, pertussis, mumps, hepatitis B, influenza, tick-borne encephalitis, staphylococcus, sal monella, meningococcus A.
- Immunoglobulins: RhoD for example.
- Extracts and diluents for: intracutaneous allergy tests, intracutaneous testing for candida, coccidioidin, histoplas min, mumps, hyposensitization therapy
- Blood and plasma products
- Topical medications: eyes, ENT area, skin
- Storing and cleaning solutions for soft contact lenses.
- Disinfectant for skin and mucous membranes
- Cosmetic creams and lotions, toothpastes, mouthwashes, pesticides.
Persistent local reactions to vaccines.
- Generalized urticaria, generalized exanthematic eruptions.
- Asthma (one case).
- Contact dermatitis.
- Contact urticaria.
- Keratoconjunctivitis (contact lens wearers).
- Acute laryngeal obstruction (throat spray).
- Prolonged external otitis (topical ear treatment).
Patch-tests with: thimerosal 0.05% in pet. (0.1% is irritant)
thiosalicylic acid 0.1% in pet.
ethylmercurychloride 0.05% in pet
3 groups of patients are to be considered
- positive to thimerosal, but negative to mercurials and thiosalicylic acid
- positive to thimerosal and thiosalicylic acid, but negative to other mercurials
- positive to thimerosal and some other mercurials, but negative to thiosalicylic acid.
The ethylmercury radical appears to be the allergenic determinant.
The high frequency of patch-test reactions to thimerosal is due to sensitization by thimerosal containing vaccines.
There is a cross-reactivity between thiosalicylate and a degraded photoproduct of
(sensitization to thimerosal with photosensitivity to piroxicam).
Hypersensitivity to thimerosal does not imply true mercury allergy. A positive patch-test with thimerosal should often be regarded as an accidental finding with no clinical relevance.
A history of ocular sensitivity to thimerosal does not preclude hepatitis B vaccine administration.
Replace thimerosal in soft contact lenses care with sterile single-unit preservative-free saline with thermal disinfection or use special preservative-free care system containing only a low concentration (0.6%) of hydrogen peroxide.