Terfenadine

In the U.S., Terfenadine was superseded by fexofenadine in the 1990s due to the risk of cardiac arrhythmia caused by QT interval prolongation.

Terfenadine is indicated for the relief of symptoms associated with seasonal allergic rhinitis such as sneezing, rhinorrhea, pruritus, and lacrimation.

Clinical studies conducted to date have not demonstrated effectiveness of Terfenadine in the common cold.

Terfenadine was withdrawn from the U.S. market in 1998.

Terfenadine is an antihistamine. Antihistamines prevent sneezing, runny nose, itching and watering of the eyes, and other allergic symptoms.

Terfenadine is used to treat allergies, hives (urticaria), and other allergic inflammatory conditions.

Terfenadine may also be used for purposes other than those listed in this medication guide.

One tablet (60 mg) twice daily for adults and pediatric patients 12 years and older.

USE OF DOSES IN EXCESS OF 60 MG B.I.D. IS NOT RECOMMENDED BECAUSE OF THE INCREASED POTENTIAL FOR QT INTERVAL PROLONGATIONS AND ADVERSE CARDIAC EVENTS..USE OF Terfenadine IN PATIENTS WITH SIGNIFICANT HEPATIC DYSFUNCTION AND IN PATIENTS TAKING KETOCONAZOLE, ITRACONAZOLE, CLARITHROMYCIN, ERYTHROMYCIN OR TROLEANDOMYCIN IS CONTRAINDICATED..

How supplied

Removed from market 1998

60 mg tablets in bottles of 100.

60 mg tablets in bottles of 500.

Tablets are round, white, and debossed "Terfenadine (Terfenadine (removed from market 1998)) ". Store tablets at controlled room temperature (59-86°F) (15-30°C). Protect from exposure to temperatures above 104°F (40°C) and moisture.

See also:
What is the most important information I should know about Terfenadine?

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.

Terfenadine is used for the treatment of allergic conditions like inflammation of eyes and nose, hives, itching and allergic sneezing. However, this drug has been withdrawn from the market due to risk of heart problems.

See also:
What other drugs will affect Terfenadine?

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.

See also:
What are the possible side effects of Terfenadine?

Cardiovascular Adverse Events

Rare reports of severe cardiovascular adverse effects have been received which include ventricular tachyarrhythmias (torsades de pointes, ventricular tachycardia, ventricular fibrillation, and cardiac arrest), hypotension, palpitations, syncope, and dizziness. Rare reports of deaths resulting from ventricular tachyarrhythmias have been received. Hypotension, palpitations, syncope, and dizziness could reflect undetected ventricular arrhythmia. IN SOME PATIENTS, DEATH, CARDIAC ARREST, OR TORSADES DE POINTES HAVE BEEN PRECEDED BY EPISODES OF SYNCOPE.. Rare reports of serious cardiovascular adverse events have been received, some involving QT prolongation and torsades de pointes, in apparently normal individuals without identifiable risk factors. There is not conclusive evidence of causal relationship of these events with Terfenadine. Although in rare cases there was measurable plasma Terfenadine, the implications of this finding with respect to the variability of Terfenadine metabolism in the normal population cannot be assessed without further study. In controlled clinical trials in otherwise normal patients with rhinitis, small increases in QTc interval were observed at doses of 60 mg b.i.d. In studies of 300 mg b.i.d. a mean increase in QTc of 10% (range -4% to +30%)(mean increase of 46 msec) was observed.

General Adverse Events

Experience from clinical studies, including both controlled and uncontrolled studies involving more than 2,400 patients who received Terfenadine, provides information on adverse experience incidence for periods of a few days up to six months. The usual dose in these studies was 60 mg twice daily, but in a small number of patients, the dose was as low as 20 mg twice a day, or as high as 600 mg daily.

In controlled clinical studies using the recommended dose of 60 mg b.i.d., the incidence of reported adverse effects in patients receiving Terfenadine was similar to that reported in patients receiving placebo..

TABLE 1 - ADVERSE EVENTS REPORTED IN CLINICAL STUDIES

In addition to the more frequent side effects reported in clinical trials, adverse effects have been reported at a lower incidence in clinical trials and/or spontaneously during marketing of Terfenadine that warrant listing as possibly associated with drug administration. These include: alopecia (hair loss or thinning), anaphylaxis, angioedema, bronchospasm, confusion, depression, galactorrhea, insomnia, menstrual disorder (including dysmenorrhea), musculoskeletal symptoms, nightmares, paresthesia, photosensitivity, rapid flare of psoriasis, seizures, sinus tachycardia, sweating, thrombocytopenia, tremor, urinary frequency and visual disturbances.

In clinical trials, severe instances of mild, or in one case, moderate transaminase elevations were seen in patients receiving Terfenadine. Mild elevations were also seen in placebo treated patients. Marketing experiences include isolated reports of jaundice, cholestatic hepatitis, and hepatitis. In most cases available information is incomplete.