Fixed drug eruption to cetirizine-role of patch testing

Antihistamines are prescribed for a wide variety of disorders like urticaria, eczema, allergies and infestations. Adverse reactions due to them is unusual and the incidence of fixed drug eruption is scarce. They are characterized by a sudden onset of edematous, erythematous plaques appearing at the same sites following an oral provocation with the drug and is proposed to be due to the epidermal CD8⁺ T cells resident at the sites of these residual post inflammatory hyper pigmented macules. Antihistamines sharing a similar chemical structure have an increased likelihood of showing cross reactions and a patch test based evaluation can be carried out to deduce the offending drugs, cross reactions and alternative medications