Astemizole (R43512, marketed under the brand name Hismanal) was a second-generation antihistamine drug that has a long duration of action. Astemizole was discovered by Janssen Pharmaceutica in 1977. It has been withdrawn from the market in most countries because of rare but potentially fatal side effects (QTc interval prolongation and related arrhythmias due to hERG channel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 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.
Astemizole may also act on histamine H3 receptors, thereby producing adverse effects.
It has been reported that this drug might prevent much of the muscle wasting (atrophy) that occurs in immobile, bedridden patients. An experiment on a small number of mice showed that astemizole blocked the activity of a protein present in muscle that is involved in muscle atrophy. However, the concerns for the drug's long-term effects on the heart preclude its routine use in humans for this indication.
Astemizole has recently been found to be a potent treatment for malaria. It has a mechanism of action similar to chloroquine but has activity even in chloroquine-resistant parasites.
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