title: Fixed drug eruption to cetirizine with positive lesional patch tests to the three piperazine derivatives.
abstract: BACKGROUND
  The H1-antihistamine cetirizine, a piperazine derivative widely used in daily practice, is rarely the cause of cutaneous drug reaction. Nevertheless, four cases of fixed drug eruption (FDE) as a result of this drug have been described recently. We present the case of a 45-year-old woman with a multilocalized FDE following oral intake of cetirizine for allergic rhinitis.
  
  
  METHODS
  Patch testing with hydroxyzine 1% and 10% in petrolatum (Chemotechnique), and with powdered Zyrtec (cetirizine) and Xyzal (levocetirizine) pills, prepared at 20% in water and at 20% in petrolatum, was performed in both residual lesions and healthy skin.
  
  
  RESULTS
  Positive results (++) to these drugs (24 h occlusion and readings at days 2 and 3) were obtained in residual lesions only. These results allowed us to confirm the drug responsible for this FDE and to study cross-reactions between antihistamines of the same chemical family.
  
  
  CONCLUSIONS
  To the best of our knowledge, this is the first report of FDE to cetirizine with positive patch testing to hydroxyzine, cetirizine, and levocetirizine. This case highlights the importance of patch testing in the study of cutaneous drug reactions, namely FDE.
authors.affiliation: Clinic of Dermatology, University Hospital, Coimbra, Portugal. mariana.cravo@netcabo.pt
authors.forename: Mariana
authors.initials: M
authors.lastname: Cravo
authors.forename: Margarida
authors.initials: M
authors.lastname: Gonçalo
authors.forename: Américo
authors.initials: A
authors.lastname: Figueiredo
mesh_terms: D017332:Cetirizine / Q000009:adverse effects*; D003429:Cross Reactions; D003875:Drug Eruptions / Q000209:etiology* / Q000473:pathology; D005260:Female; D039563:Histamine H1 Antagonists, Non-Sedating / Q000009:adverse effects*; D006801:Humans; D008875:Middle Aged; D010328:Patch Tests; D010879:Piperazines; D006255:Rhinitis, Allergic, Seasonal / Q000188:drug therapy; D012867:Skin / Q000473:pathology
chemical_list: D039563:Histamine H1 Antagonists, Non-Sedating; D010879:Piperazines; D017332:Cetirizine