The two first H1-antihistamines without sedating effect to be marketed were terfenadine and astemizole.
They were withdrawn from the market because they could induce ventricular arrhrythmias, prolongation of QT interval which can lead to torsades de pointes.
They have a longer duration of action and longer plasma half-life than the first generationdrugs, which makes it possible to reduce the number of daily intakes.
By their alpha-adrenolytic effect especially when they are given by parenteral route, they could reduce the vasoconstrictive effect of adrenaline, administered for example in case of anaphylactic shock.
Oxatomide, is a sedating H1-antihistamine, having mast-cell stabilising properties perhaps by a calcium-channel antagonist effect , without anticholinergic effect.
It is used in treatment of chronic urticaria, atopic dermatitis and dermographisms. Doxylamine is a sedating antihistamine also used as an hypnotic.
In case of overdose, loratadine can cause sedation and antimuscarinic effects.
Cetirizine, carboxyl derivative of hydroxyzine which is used as a sedative and anxiolytic, in addition to its H1-antihistamine effect, inhibits release of various cytokines and leukotrienes.
Certain H1 antagonists, such as promethazine, have a local anesthetic effect.