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Terfenadine (C₃₂H₄₁NO₂; MW 471.7 g/mol) was a second-generation antihistamine (brand: Seldane), now withdrawn.
Structure: Features a diphenylmethylpiperidine core linked to a *4-tert-butylphenyl ketone* chain.
Mechanism: H₁-receptor antagonist blocking histamine (non-sedating).
Prodrug: Metabolized to active fexofenadine (Allegra®).
Withdrawal (1997):
Inhibits cardiac hERG potassium channels → QT prolongation → risk of fatal arrhythmia (torsades de pointes).
Toxic buildup if taken with CYP3A4 inhibitors (e.g., grapefruit juice, antifungals).
Legacy:
Catalyst for stricter cardiac safety screening in drug development.
Replaced by safer metabolite fexofenadine (carboxylic acid analog).
Terfenadine (brand name Seldane) is a second-generation antihistamine that was withdrawn from the market due to cardiac risks. Here’s its chemical profile:
IUPAC Name:
1-(4-tert-Butylphenyl)-4-[4-(hydroxydiphenylmethyl)piperidin-1-yl]butan-1-one
Molecular Formula:
C₃₂H₄₁NO₂ (MW = 471.68 g/mol).
Structure:
Diphenylmethylpiperidine core (antihistamine pharmacophore).
4-tert-Butylphenyl ketone side chain (metabolic hotspot).
Hydroxy group at the benzhydryl position.
tert-Butyl-C₆H₄-C(O)-(CH₂)₃-N
|
(C₆H₅)₂C-OH
H₁-Receptor Antagonist: Blocks histamine receptors without crossing the blood-brain barrier (minimized sedation vs. first-gen antihistamines).
Prodrug: Metabolized to active fexofenadine (Allegra®).
Cardiotoxicity: Inhibits cardiac hERG potassium channels → QT prolongation → risk of torsades de pointes (fatal arrhythmia).
CYP3A4 Interaction: Metabolism inhibited by grapefruit juice/azole antifungals → toxic accumulation of parent drug.
Withdrawn globally (1997–1998) and replaced by fexofenadine.
Landmark case in drug safety illustrating risks of hERG inhibition and CYP-mediated interactions.
Fexofenadine (its metabolite) remains a widely used non-sedating antihistamine.
| Terfenadine | Fexofenadine (Active Metabolite) |
|---|---|
| Ketone group | Carboxylic acid group (-COOH) |
| Cardiotoxic | Safe (no hERG inhibition) |
| CYP3A4 substrate | Renal excretion |
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