Thimerosal in the detection of clinically relevant allergic contact reactions

Thimerosal, a mercuric derivative of thiosalicylic acid, is a preservative used in several types of consumer products, including cosmetics, ophthalmic and otolaryngologic medications, and vaccines. As a result of allergic rea ctions and environmental concerns, its use has declined significantly durin g the past 2 decades. During a 5-year study at the University of Kansas Med ical Center, 574 patients were patch tested to the North American Contact D ermatitis Group's standard allergen tray which included thimerosal. The dem ographic data from thimerosal-allergic and nonallergic persons were compare d. Statistically significant increases in thimerosal allergy were found amo ng women, health care workers, secretaries, and cooks. Thimerosal-allergic persons were more likely to be allergic to neomycin, bacitracin, and tixoco rtol pivalate. Despite a high percentage of thimerosal-allergic patients in our test population, very few of these allergic reactions were found to be clinically relevant to the patient's current dermatologic condition. Using the Significance-Prevalence Index Number for thimerosal and contrasting th is number with the Significance-Prevalence Index Number for other allergens on the North American Contact Dermatitis Group's standard tray, we propose that either ethyleneurea/melamine formaldehyde or bacitracin would be more useful than thimerosal as a commercially available screening allergen.