Therefore, based on our results, in an in vivo context astemizole might potentiate calcitriol antineoplastic effects by inhibiting its degradation, while at the same time calcitriol may prevent astemizole side effects such as cardiac arrhythmias or torsades de pointes by stimulating CYP3A4 expression. This evidence concerns the gene CYP3A4 and cardiac arrhythmia.