Cetirizine (Zyrtec, and others) and cetirizine/pseudoephedrine (Zyrtec-D) are becoming available without a prescription this month for treatment of allergic rhinitis and urticaria in adults and children. Cetirizine is the second of the second-generation H1-antihistamines to become available over the counter. Loratadine (Claritin, and others) was the first.

Cetirizine has been shown to be more effective than loratadine in suppressing histamine-induced wheals in healthy volunteers (W Carey et al. Drugs Exp Clin Res 2002; 28:243), but no well-controlled clinical trials have established that any second-generation H1-antihistamine is more effective overall than any other (M Plaut and MD Valentine. N Engl J Med 2005; 353:1934).

Cetirizine may be mildly sedating in some patients, but it is significantly less sedating than first-generation H1-antihistamines such as diphenhydramine (Benadryl, and others) or chlorpheniramine (Chlor-Trimeton, and others), which have been available without a prescription for many years. Its safety in young children is better documented than that of any other first- or second-generation H1-antihistamine (Treat Guidel Med Lett 2007; 5:71).