Purity >98%. Astemizole is a non-sedating antihistamine that antagonizes the histamine H1 receptor with a Ki value of 4.4 nM. It is considerably less potent at muscarinic acetylcholine receptors (Ki = 2.4 μM). Astemizole is also a potent blocker of ether-a-go-go-related gene (ERG) potassium channels (IC50 = ~1 nM) that has been used to study long QT syndrome type 2. Furthermore, because it can target oncogenic ERG1 and ERG potassium channels, astemizole has been explored as a potential antineoplastic agent for decreasing proliferation of various cancer cells.