Maculopapular and urticarial eruption from cetirizine

Fexofenadine-induced urticaria

Fexofenadine (Allegra® 180) is a second-generation antihistamine. It is widely used as anti-allergic drug, which suppresses various allergic reactions mediated by histamines. A few cases of H1-antihistamine-induced urticaria have been reported. Herein, we report a rare case of fexofenadine-induced urticaria which was confirmed by a prick test, oral provocation test, and flow cytometry assisted-basophil activation test.

Second-Generation Antihistamines

Antihistamines are useful medications for the treatment of a variety of allergic disorders. Second-generation antihistamines avidly and selectively bind to peripheral histamine H1 receptors and, consequently, provide gratifying relief of histamine-mediated symptoms in a majority of atopic patients. This tight receptor specificity additionally leads to few effects on other neuronal or hormonal systems, with the result that adverse effects associated with these medications, with the exception of noticeable sedation in about 10% of cetirizine-treated patients, resemble those of placebo overall. Similarly, serious adverse drug reactions and interactions are uncommon with these medicines. Therapeutic interchange to one of the available second-generation antihistamines is a reasonable approach to limiting an institutional formulary, and adoption of such a policy has proven capable of creating substantial cost savings. Differences in overall efficacy and safety between available second-generation antihistamines, when administered in equivalent dosages, are not large. However, among the antihistamines presently available, fexofenadine may offer the best overall balance of effectiveness and safety, and this agent is an appropriate selection for initial or switch therapy for most patients with mild or moderate allergic symptoms. Cetirizine is the most potent antihistamine available and has been subjected to more clinical study than any other. This agent is appropriate for patients proven unresponsive to other antihistamines and for those with the most severe symptoms who might benefit from antihistamine treatment of the highest potency that can be dose-titrated up to maximal intensity.

Cutaneous drug eruption from cetirizine and hydroxyzine

Topical application of the antihistamines commonly leads to sensitization for patients, but skin reactions provoked by their systemic use are very rare. The antihistamines cetirizine and hydroxyzine are piperazine derivatives, on the structural basis of an ethylenediamine, but the cross-reactions between the 2 have rarely been reported. A 44-year-old man visited because of the generalized morbilliform eruptions with pruritus over his whole body, after intake of hydroxyzine (Ucerax) and azelastine (Azeptine), administered during a 2-day period for chronic urticaria. Previously, he had presented the same cutaneous reactions after oral administration of cetirizine (Lotec). Oral challenge tests performed with cetirizine and hydroxyzine led to the same cutaneous reactions. He was given the diagnosis of drug eruption from cetirizine and hydroxyzine, which suggests that there were cross-reactions among cetirizine, hydroxyzine, and ethylenediamine.

Urticarial intolerance reaction to cetirizine

The paradoxical acute exacerbation of pre-existing chronic idiopathic urticaria accompanied by intense generalized pruritus, facial oedema, and dyspnoea in a 36-year-old-woman 3-4 h after a single oral dose of 10 mg cetirizine (Zyrtec tablets), suggested the presence of an underlying intolerance reaction. However, a type I hypersensitivity reaction also had to be excluded. Detailed allergy testing supported the view that the patient had suffered an intolerance reaction to cetirizine. This is the third known case of most probably a nonallergic generalized urticaria following the administration of cetirizine, a drug with extensive usage worldwide. However a type I sensitization to cetirizine is indeed possible, as has been demonstrated in this research with the verification of cetirizine-specific IgE antibodies in one of the control sera.