Drug information of 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In the U.S., Terfenadine was superseded by fexofenadine in the 1990s due to the risk of cardiac arrhythmia caused by QT interval prolongation.
Mechanism of effect
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.
Terfenadine, an H1-receptor antagonist antihistamine, is similar in structure to astemizole and haloperidol, a butyrophenone antipsychotic. The active metabolite of terfenadine is fexofenadine.
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%
Protein binding: 70%
Metabolism: Hepatic, Terfenadine to fexofenadine
Half life: 3.5 hours
Terfenadine is usually taken twice a day, in the morning and the evening.
Side effectsDiarrhea , Headache , nausea , dry mouth , vertigo , dry skin , difficulty urinating , Restlessness , Abdominal discomfort
InteractionsTinidazole , Zafirlukast , Fluphenazine , Ranolazine , Darunavir , Sodium Oxybate , Nefazodone , ritonavir , nelfinavir , Zileuton , Droperidol , Procainamide , Indapamide , Efavirenz , Tipranavir , Halofantrine , Grepafloxacin , Mibefradil , Delavirdine , Amiodarone , Aprepitant , Adenosine , Erythromycin , Itraconazole , Papaverine , vemurafenib , Ceritinib , conivaptan , Bepridil , Pasireotide , bedaquiline , levomethadyl acetate , Gatifloxacin , Iloperidone , ivosidenib , Crizotinib , Cabozantinib , Troleandomycin , Ribociclib , Dofetilide , Ibutilide , Anagrelide , Lumefantrine / artemether , Arsenic trioxide , Telithromycin , Quinine , sparfloxacin , Indinavir , Mesoridazine , Panobinostat , Amprenavir , Fosamprenavir , Ivabradine , Mifepristone , Dolasetron , vandetanib , Atazanavir , Toremifene , Quinidine , Ziprasidone , dronedarone , saquinavir , Clarithromycin , Clotrimazole , Clozapine , Bicalutamide , escitalopram , miconazol , Methadone , Moxifloxacin , Nilotinib , Haloperidol , Voriconazole , Ketoconazole , Citalopram , Cisapride , Fluvoxamine , Fluoxetine , Fluconazole , Fingolimod , Posaconazole , Pimozide , Thioridazine , Disopyramide , Cimetidine , Sotalol , Bendroflumethiazide , Lercanidipine , Lorlatinib , Roxithromycin , oleandomycin , Blonanserin , Vernakalant , tucatinib , Remoxipride
- asthma or another lung disease;
- low potassium levels in your blood;
- urinary retention or an enlarged prostate;
- kidney or liver disease; or
- heart disease, especially an irregular heartbeat.
Points of recommendation
Take terfenadine as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
Take each dose with a full glass (8 ounces) of water.
Do not crush, break, or chew the tablets. Swallow them whole.
Never take more of this medication than is directed by your doctor. If your symptoms are not being adequately treated, talk to your doctor.
Store terfenadine at room temperature away from moisture and heat.
Take the missed dose as soon as you remember. However, if it is almost time for your next dose, skip the missed dose and take only your next regularly scheduled dose. Do not take a double dose of this medication.
Use caution when driving, operating machinery, or performing other hazardous activities. Terfenadine may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.
Use alcohol cautiously. Alcohol may increase drowsiness and dizziness while you are taking terfenadine.