Terfenadine

Products

Terfenadine (Teldane tablets/suspension) is no longer on the market in many countries. Possible alternatives are the successor product fexofenadine (Telfast) or other 2nd generation antihistamines.

Structure and properties

Terfenadine (C32H41NO2, Mr = 471.7 g/mol) is a racemate. It exists as a white crystalline powder that is very sparingly soluble in water. Terfenadine is a prodrug that is biotransformed by CYP3A4 to the active metabolite fexofenadine (carboxy-terfenadine). Fexofenadine is also approved as a drug (Telfast) and has a long half-life. Unlike the parent compound, it is not cardiotoxic.

Effects

Terfenadine (ATC R06AX12) has antihistamine and antiallergic properties. The effects are due to selective antagonism at histamine H1 receptors.

Indications

For the treatment of hay fever, allergic rhinitis, urticaria, and allergic conjunctivitis.

Dosage

According to the SmPC. Tablets may be administered as a single daily dose. Terfenadine should not be taken with grapefruit juice.

Contraindications

Terfenadine is contraindicated in the presence of hypersensitivity, hepatic impairment, along with strong CYP3A4 inhibitors, and prolongation of the QT interval. For complete precautions and drug-drug interactions, see the Drug Information Leaflet.

Interactions

Terfenadine is a substrate of CYP3A4. Concomitant administration of CYP inhibitors may lead to accumulation and cause prolongation of the QT interval, which may result in life-threatening cardiac arrhythmias.

Adverse effects

The most serious potential adverse effect may be prolongation of the QT interval, resulting in life-threatening cardiac arrhythmias. Possible symptoms include palpable heartbeats, low blood pressure, dizziness, loss of consciousness, and convulsions.