Allergic contact dermatitis from tacrolimus.

A 9-year-old boy developed allergic contact dermatitis from tacrolimus ointment. Tacrolimus was proven to be the allergen by right-versus-left double-blinded provocative use testing of tacrolimus ointment 0.1% versus inactive vehicle applied twice daily to normal preauricular and antecubital skin. Facial dermatitis appeared after 1 week and antecubital dermatitis after 7 weeks. Furthermore, patch testing of each individual ingredient was positive only with tacrolimus; a concentration of 2.5% in ethanol was required. Forty control patients had negative patch tests with tacrolimus 5% in ethanol. We hypothesize that the unusually long time required to elicit a positive use test on the arm and the high patch test concentration required on the back are caused by low percutaneous absorption through normal extrafacial skin. This is likely to be caused in part by the high molecular weight of tacrolimus. A similar phenomenon may occur when patch testing with neomycin sulfate.