Hydroxyzine hydrochloride is a piperazine derivative, structurally based on a dimer of ethylenediamine and possessing antihistaminic and anticholinergic activity.
Positive patch-tests to ethylenediamine.
Cutaneous: urticaria, eczema, fixed drug eruption (oral or genital mucous membrane, after 6 hours or more), systemic contact dermatitis (baboon syndrome, vesicular hand eczema, toxico derma-like rash).
Patch-tests with hydroxyzine 2%, 5%, 10% aq.
M.I.F (macrophage migration inhibitory factor): positive in some cases of fixed drug eruption.
The drug may act as a hapten and bind to protein components or receptor cells of the lower dermis. This complex is similarly presented to the Langherans cells as in contact dermatitis (fixed drug eruption).
Cross-reactions among ethylenediamine, hydroxyzine, and cetirizine are influenced by sensitivity to diethylenediamine (common piperazinic ring).
Generally, patients sensitive to hydroxyzine are also sensitive to ethylenediamine.