astemizole astemizole astemizole (marketed under the brand name hismanal, developmental code r43512) was a second-generation antihistamine drug that has a long duration of action. astemizole was discovered by janssen pharmaceutica in 1977. it was withdrawn from the market globally in 1999 because of rare but potentially fatal side effects (qtc interval prolongation and related arrhythmias due to herg channel blockade). astemizoleclinical dataahfs/drugs.commultum consumer informationmedlineplusa600034pregnancycategory c (usa) routes ofadministrationoralatc coder06ax11 (who) legal statuslegal status withdrawn pharmacokinetic dataprotein binding~96%metabolismhepatic (cyp3a4)elimination half-life24 hoursexcretionfecalidentifiers iupac name 1--n--4-piperidyl]benzoimidazol-2-amine cas number68844-77-9 ypubchem cid2247iuphar/bps2603drugbankdb00637 ychemspider2160 yunii7hu6337315keggd00234 ychebichebi:2896 ychemblchembl296419 ycomptox dashboard (epa)dtxsid9020110 echa infocard100.065.837 chemical and physical dataformulac28h31fn4omolar mass458.581 g·mol−13d model (jsmol)interactive image smiles fc1ccc(cc1)cn2c5ccccc5nc2nc4ccn(ccc3ccc(oc)cc3)cc4 inchi inchi=1s/c28h31fn4o/c1-34-25-12-8-21(9-13-25)14-17-32-18-15-24(16-19-32)30-28-31-26-4-2-3-5-27(26)33(28)20-22-6-10-23(29)11-7-22/h2-13,24h,14-20h2,1h3,(h,30,31) ykey:gxdalqbwzgodgz-uhfffaoysa-n y (verify) pharmacology astemizole is a histamine h1-receptor antagonist. it has anticholinergic and antipruritic effects. astemizole is rapidly absorbed from the gastrointestinal tract and 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. astemizole does also act as fiasma (functional inhibitor of acid sphingomyelinase). toxicity astemizole has an oral ld50 of approximately 2052 mg/kg (in mice).