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Active ingredient: Terfenadine - Brands, Medical Use, Clinical Data

Brands, Medical Use, Clinical Data

Drug Category

  • Antiarrhythmic Agents
  • Anti-allergic Agents
  • Antihistamines

Dosage Forms

  • Oral tablets

Brands / Synonyms

Aldaban; Allerplus; Cyater; Nebralin; Seldane; Teldane; Teldanex; Terdin; Terfex; Ternadin; Triludan

Indications

For the treatment of allergic rhinitis, hay fever, and allergic skin disorders.

Pharmacology

Terfenadine, an H1-receptor antagonist antihistamine, is similar in structure to astemizole and haloperidol, a butyrophenone antipsychotic. The active metabolite of terfenadine is fexofenadine.

Mechanism of Action

Terfenadine competes with histamine for binding at H1-receptor sites in the GI tract, uterus, large blood vessels, and bronchial muscle. This reversible binding of terfenadine to H1-receptors suppresses the formation of edema, flare, and pruritus resulting from histaminic activity. As the drug does not readily cross the blood-brain barrier, CNS depression is minimal.

Absorption

On the basis of a mass balance study using 14C labeled terfenadine the oral absorption of terfenadine was estimated to be at least 70%

Toxicity

Mild (e.g., headache, nausea, confusion), but adverse cardiac events including cardiac arrest, ventricular arrhythmias including torsades de pointes and QT prolongation have been reported. LD50=mg/kg (orally in mice)

Biotrnasformation / Drug Metabolism

Hepatic

Contraindications

CONCOMITANT ADMINISTRATION OF TERFENADINE WITH KETOCONAZOLE (NIZORAL) OR ITRACONAZOLE (SPORONOX) IS CONTRAINDICATED. TERFENADINE IS ALSO CONTRAINDICATED IN PATIENTS WITH DISEASE STATES OR OTHER CONCOMITANT MEDICATIONS KNOWN TO IMPAIR ITS METABOLISM, INCLUDING SIGNIFICANT HEPATIC DYSFUNCTION, AND CONCURRENT USE OF CLARITHROMYCIN, ERYTHROMYCIN, OR TROLEANDOMYCIN. QT PROLONGATION HAS BEEN DEMONSTRATED IN SOME PATIENTS TAKING TERFENADINE IN THESE SETTINGS, AND RARE CASES OF SERIOUS CARDIOVASCULAR EVENTS, INCLUDING DEATH, CARDIAC ARREST, AND TORSADES DE POINTES, HAVE BEEN REPORTED IN THESE PATIENT POPULATIONS..

Terfenadine is contraindicated in patients with a known hypersensitivity to terfenadine or any of its ingredients.

Drug Interactions

Ketoconazole

Spontaneous adverse reaction reports of patients taking concomitant ketoconazole with recommended doses of terfenadine demonstrate QT interval prolongation and rare serious cardiac events, e.g. death, cardiac arrest, and ventricular arrhythmia including torsades de pointes. Pharmacokinetic data indicate that ketoconazole markedly inhibits the metabolism of terfenadine, resulting in elevated plasma terfenadine levels. Presence of unchanged terfenadine is associated with statistically significant prolongation of the QT and QTc intervals.Concomitant administration of ketoconazole and terfenadine is contraindicated.

Itraconazole

Torsades de pointes and elevated parent terfenadine levels have been reported during concomitant use of terfenadine and itraconazole in clinical trials of itraconazole and from foreign post-marketing sources. One death has also been reported from foreign post- marketing sources. Concomitant administration of itraconazole and terfenadine is contraindicated.

Due to the chemical similarity of other azole-type antifungal agents (including fluconazole, metronidazole, and miconazole) to ketoconazole, and itraconazole, concomitant use of these products with terfenadine is not recommended pending full examination of potential interactions.

Macrolides

Clinical drug interaction studies indicate that erythromycin and clarithromycin can exert an effect on terfenadine metabolism by a mechanism which may be similar to that of ketoconazole, but to a lesser extent. Although erythromycin measurably decreases the clearance of the terfenadine acid metabolite, its influence on terfenadine plasma levels is still under investigation. A few spontaneous accounts of QT interval prolongation with ventricular arrhythmia including torsades de pointes, have been reported in patients receiving erythromycin or troleandomycin.

Concomitant administration of terfenadine with clarithromycin, erythromycin, or troleandomycin is contraindicated: Pending full characterization of potential interactions, concomitant administration of terfenadine with other macrolide antibiotics, including azithromycin, is not recommended. Studies to evaluate potential interactions of terfenadine with azithromycin are in progress.

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