Astemizole was a second-generation antihistamine drug that has a long duration of action. It has been withdrawn from the market in most countries because of rare but potentially fatal side effects (QTc interval prolongation and related arrhythmias due to hERG channel blockade). Astemizole is a histamine H1-receptor antagonist. It is structurally similar to terfenadine and haloperidol (a butyrophenone antipsychotic). It has anticholinergic and antipruritic effects. Astemizole competitively binds to histamine H1-receptor sites in the gastrointestinal tract, uterus, blood vessels, and bronchial muscle. This suppresses the formation of edema and pruritus (caused by histamine). Despite some earlier reports that Astemizole does not cross the blood–brain barrier, several studies have shown high permeability and high binding to protein folds associated with Alzheimer's.
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