Background and design: Several topical antihistamines are known to cause contact allergy. Premarket predictive patch testing with doxepin cream showed it to have "low risk of irritation and sensitization" on normal human skin. In our patch test clinic, we routinely test topical preparations, and over a recent 1-year period, we patch-tested doxepin cream, the standard screening tray, and other topical preparations on 97 patients with various pruritic dermatoses. When possible, patients with positive reactions to doxepin cream were patch-tested with its ingredients, and repeated open-application use tests were also performed with the product.
Results: Seventeen patients had relevant positive patch test reactions to doxepin cream and 80 had negative reactions. In 13 of the 17 patients with positive reactions, the diagnosis of allergic contact dermatitis to doxepin cream was confirmed by positive patch test reactions to both the active ingredient and the whole formulation of doxepin cream, by an observed positive use test reaction to doxepin cream, or by both. Of 14 patients who completed testing with doxepin cream ingredients, all had positive reactions to the whole formulation, and 12 had positive reactions to doxepin hydrochloride. Repeated open-application use tests with doxepin cream on normal skin resulted in positive eczematous responses in eight of 10 patients. Eight of the 17 patients had concurrent, relevant positive reactions to other patch tests, especially to fabric-finish resins and to ingredients of other topical preparations. Many had long-standing dermatitis, and each had used doxepin cream for several days to 1 year. Two patients appeared to have had systemic contact dermatitis.
Conclusions: Diagnostic patch test clinic experience illustrates that doxepin cream is a contact sensitizer on inflamed skin. Oral doxepin should be avoided in patients with doxepin contact allergy.