Antihistamine antiallergic drugs are divided into the first generation antihistamines such as diphenhydramine, chlorpheniramine and promethazine, the second generation antihistamines such as terfenadine and astemizole, and the third generation antihistamines such as fexofenadine and levocetirizine. At present, the second generation antihistamines are mainly used in clinic in China.