This antihistaminic drug can cause cardiac arrhythmia at high dose by blocking cardiac K+ channels. It is most likely to be:

The drugs which can cause QT prolongation and Torsades' de pointes and have been withdrawn from the market due to this reason are: C: Cisapride A: Astemizole T: Terfenadine You can remember CAT is cute, so these drugs cause QT prolongation.