Allergy to mercurochrome and rifamycin

The authors describe contact dermatitis to mercurochrome and rifamycin in an 11-year-old boy. In July 1983, he injured his left elbow, with lacerations and contusions which were treated with topical mercurochrome and rifamycin. These minor wounds did not heal as rapidly as expected and the physician changed to tetracycline ointment. In December 1983, the boy injured himself again, this time on the right leg, and his parents, on their own initiative, re-applied mercurochrome and rifamycin, setting off a dermatitis with erythema and blisters at the site of application and later extending to the antecubital folds. The use of mercurochrome and rifamycin was stopped. When the rash had cleared, the authors patch tested him to the ICDRG standard series, rifamycin, mercurochrome, mercuric chloride and mercurous phenylacetate. There were positive reactions to mercurous ammonium chloride, mercurochrome, mercuric chloride and rifamycin, but no reaction to mercurous phenylacetate. They publish this case because of the rarity of sensitization to mercurochrome, and the even greater rarity of sensitization to rifamycin. Since these 2 products have no chemical affinity, it is an example of concomitant sensitization.