Astemizole (Molecule of the Month for March 2002)
This is a non-sedating anti-histamine, which is only available on prescription.
It is used for the treatment of seasonal allergies and hives, and it consists of a 10mg tablet.
It is a selective and long-lasting drug that works specifically to prevent histamine release, together with the release of itís associated mediator, and so blocking the pathway of the immune response, which is associated with these symptoms. It is long-lasting as it dissociates very slowly from the biochemical receptors in question, so acts for a very long time.
In general, most side effects are minor and short-lived and comprise such problems as weight gain, appetite increase, abdominal pain, nausea, diarrhoea, drowsiness and headache, which are generally minor symptoms and not particularly serious. However, there are a number of serious side effects, some to watch for being spasm of the bronchioles, dangerous changes in liver enzyme levels and allergic reactions, which may be fatal if they affect the nose, mouth or throat area, where any such swelling like that caused by such auto-immune responses can be extremely dangerous and life-threatening. However, the main serious side-effect is the possibility of major cardio-vascular effects, ranging from changes in heart rhythm, through to possible heart attack.
The possibility of cardio-vascular effects is greatly increased when astemizole is taken in excess dosage, or when it is taken in combination with certain other pharmaceutical substances, which have the property of magnifying itís effects.
On the 28/10/92, the FDA issued a warning stating that it should not be taken in combination with the anti-fungals ketoconazole and itraconazole, or with the anti-biotic erythromycin, as they have been associated with cardio-vascular problems relating from the mixing of these chemicals.
Also, on the 25/3/96, the producers, Janssen Pharmaceutica, sent a letter to healthcare professionals, stating the above and also stating that high levels of Quinine (>430mg daily) could also interact with astemizole, which, as with the other chemicals, results in elevated blood plasma levels of astemizole and itís major metabolite, desmethylastemizole, which are the cause of the cardio-vascular problems. The only other side effect is impaired hepatic function, which is also a serious problem, and ought to be watched.
Formal Chemical Name (IUPAC)
Update by Karl Harrison
(Molecule of the Month for March 2002 )