Thimerosal Allergy and Clinical Relevance in Thailand
Penpun Wattanakrai MD*, Natta Rajatanavin MD*
Affiliation : * Division of Dermatology, Department of Medicine, Ramathibodi Hospital, Mahidol University
Background : Thimerosal or merthiolate is used as an antiseptic and a preservative in topical medicaments,
cosmetics, and vaccines. Thimerosal is known to cause delayed type hypersensitivity. However, there is argu-
ment about the clinical relevance and risk of using thimerosal-preserved products in thimerosal allergic
individuals.
Objective : Retrospective review of patch test results from the Ramathibodi Hospital patch test clinic to deter-
mine the prevalence and relevance of allergic reactions to thimerosal in Thailand.
Materials and Methods : During a 5-year period, thimerosal was patch tested in all patients tested for possible
allergic contact dermatitis. Thimerosal was the second most common allergen causing a positive patch test
reaction.
Results : Of the 433 patients tested, 46 (10.62%) were positive to thimerosal. However, despite the high
prevalence of positive reactions none was clinically relevant to their present dermatitis, none of the patients
reported reactions to vaccination or cross-reaction to piroxicam.
Conclusion : There was a high rate of sensitization to thimerosal in Thai patients, but were of little clinical
relevance. The author does not advise thimerosal allergic individuals to avoid vaccination, although the
small risk of local dermatitis should be pointed out. The topical use of thimerosal containing antiseptics
should be avoided.
Keywords : Allergic contact dermatitis, Patch test, Thimerosal, Merthiolate
