Terfenadine

1 : 1 mixture (racemate)
Terfenadine

Systematic (IUPAC) name
(RS)-1-(4-tert-butylphenyl)-4-{4-[hydroxy(diphenyl)methyl]piperidin-1-yl}-butan-1-ol
Identifiers
CAS number	50679-08-8
ATC code	R06AX12
PubChem	5405
DrugBank	APRD00606
Chemical data
Formula	C32H41NO2
Mol. mass	471.673 g/mol
Pharmacokinetic data
Bioavailability	?
Protein binding	70%
Metabolism	?
Half life	3.5 hours
Excretion	?
Therapeutic considerations
Pregnancy cat.	?
Legal status	Withdrawn
Routes	?
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Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was marketed under various brand names including Seldane in the United States, Triludan in the United Kingdom, and Teldane in Australia. It was superseded by fexofenadine in the 1990s due to the risk of cardiac arrhythmia caused by QT interval prolongation.

Terfenadine is a prodrug, generally completely metabolised to the active form fexofenadine by the intestinal cytochrome P450 CYP3A4 isoform. Due to this presystemic gut wall metabolism terfenadine normally is not measurable in the plasma. Terfenadine itself, however, has a cardiotoxic effect in higher doses while its metabolites have no such effect. 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 like grapefruit. The addition of or dosage change in these CYP3A4 inhibitors makes it harder for the body to metabolize and remove the drug. Terfenadine appears in larger concentrations in plasma leading to toxic effects on the heart's rhythm and electrical conduction like ventricular tachycardia and torsades de pointes.

In early 1997, the U.S. Food and Drug Administration (FDA) recommended that the terfenadine-containing drugs be removed from the market and that physicians consider alternative medications for their patients. Seldane was formally removed from the U.S. market in late 1997 after the approval of Allegra, a drug by the same maker as Seldane that was not found to cause the potentially fatal heart condition.^[1] Terfenadine-containing drugs were subsequently removed from the Canadian market in 1999,^[2] and are no longer available for prescription in the UK.^[3]

References

1. ^ Fda Approves Allegra-D, Manufacturer To Withdraw Seldane From Marketplace
2. ^ Status of Terfenadine-Containing Drugs in Canada
3. ^ Terfenadine- General Practice notebook

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