Astemizole

Astemizole (R 43512), a second-generation antihistamine drug to diminish allergic symptoms with a long duration of action, is a histamine H1-receptor antagonist, with an IC₅₀ of 4 nM. Astemizole also shows potent hERG K⁺ channel blocking activity with an IC₅₀ of 0.9 nM. Astemizole has antipruritic effects^[1][2]. In Vivo: Astemizole (p.o., 10 and 30 mg/kg) and (i.v., 1 and 3 mg/kg) has no effect on respiratory rate, heart rate and blood pressure, and even at high doses of 30 mg/kg and 3 mg/kg, also has no effect on body temperature and exercise capacity in male common marmosets. But Astemizole can prolong the QT interval and induce premature ventricular contractions at 30 mg/kg (po) and 1 mg/kg (iv)^[3].
Astemizole (p.o., 3 and 30 mg/kg) shows that the pre-drug control values (C) of the idioventricular rate, QT interval and QTcF are 31 beats/min, 319 ms and 256 at dose of 3 mg/kg, while those are 31 beats/min, 331 ms and 270 at dose of 30 mg/kg, respectively in mice. Moreover, Astemizole at a dose of 30 mg/kg (po) may cause tip-twisting ventricular tachycardia by inhibiting hERG K⁺ channels^[4].