Antihistaminic drugs can be classified into first and second generation types. First generation drugs include seven classes such as propylamines, ethanolamines, ethylenediamines, phenothiazines, piperazines, heptanes, and phthalazinone. Second generation drugs are peripherally selective and include two classes: piperazines such as cetirizine/levocetirizine and piperidines such as fexofenadine, loratadine/desloratadine.