<unk>  is an antihistamine formerly used for the treatment of allergic conditions. It was brought to market by Hoechst Marion Roussel (now Sanofi-Aventis) and marketed under various brand names, including Seldane in the United States, Triludan in the United Kingdom, and Teldane in Australia.  According to its manufacturer,<unk>  had been used by over 100 million patients worldwide as of 1990.It was superseded by fexofenadine in the 1990s due to the risk of a particular type of disruption of the electrical rhythms of the heart (specifically cardiac arrhythmia caused by QT interval prolongation).<unk>  is a prodrug, generally completely metabolized to the active form fexofenadine in the liver by the enzyme cytochrome P450 CYP3A4 isoform.
Due to its near complete metabolism by the liver immediately after leaving the gut,<unk>  normally is not measurable in the plasma.<unk>  itself, however, is cardiotoxic at higher doses, while its major active metabolite is not.<unk> , in addition to its antihistamine effects, also acts as a potassium channel blocker (Kv11.1 encoded by the gene hERG). Since its active metabolite is not a potassium channel blocker, no cardiotoxicity is associated with fexofenadine.Toxicity is possible after years of continued use with no previous problems as a result of an interaction with other medications such as erythromycin, or foods such as grapefruit. The addition of, or dosage change in, these CYP3A4 inhibitors makes it harder for the body to metabolize and remove<unk> . In larger plasma concentrations, it may lead to toxic effects on the heart's rhythm (e.g. ventricular tachycardia and torsades de pointes).
Terfenadine
Loratadine
Olopatadine 
Budesonide 
Desloratadine
Chloropyramine
Dihydroergotamine 
Ecallantide