Clarithromycin
Contraindicated
Textbook-cited
Dangerous ventricular arrhythmia (QT prolongation, torsades de pointes)
Concurrent use is contraindicated
Source: KDT 7e · p948
Drug reference
terfenadine
Antihistamine
Antihistamine
CDSCO approved
EXCRETION
—
not curated
INTERACTIONS
12 major
incl. contraindicated
PREGNANCY
—
not curated
Top interactionssee all 12 →
- ClarithromycinContraindicatedTextbook-citedKDT 7e · p948
- ErythromycinContraindicatedTextbook-citedKDT 7e · p948
- FluconazoleContraindicatedTextbook-citedKDT 7e · p948
- ItraconazoleContraindicatedTextbook-citedKDT 7e · p948
Mechanism
Terfenadine is a prodrug that requires oxidation by CYP3A4 to its active metabolite. Inhibition of its metabolism results in elevated plasma levels of the parent compound.
Pharmacokinetics
Metabolism
Terfenadine is a substrate of CYP3A4/5.
Contraindications
- Coadministration with CYP3A4 inhibitors (e.g., erythromycin, grapefruit juice)
- High doses (risk of arrhythmias)
Side effects
Serious
- Ventricular tachycardia
- Arrhythmias
Drug interactions
Erythromycin
Contraindicated
Textbook-cited
Dangerous ventricular arrhythmia (QT prolongation, torsades de pointes)
Concurrent use is contraindicated
Source: KDT 7e · p948
Fluconazole
Contraindicated
Textbook-cited
Dangerous ventricular arrhythmia (QT prolongation, torsades de pointes)
Concurrent use is contraindicated
Source: KDT 7e · p948
Itraconazole
Contraindicated
Textbook-cited
Dangerous ventricular arrhythmia (QT prolongation, torsades de pointes)
Concurrent use is contraindicated
Source: KDT 7e · p948
Ketoconazole
Contraindicated
Textbook-cited
Dangerous ventricular arrhythmia (QT prolongation, torsades de pointes)
Concurrent use is contraindicated
Source: KDT 7e · p948
Adenosine
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Amiodarone
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Amisulpride
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Amprenavir
Severe
Database
Drug interaction classified as: metabolism
Source: DDInter
Anagrelide
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Aprepitant
Severe
Database
Life-threatening QT prolongation.
Aprepitant is contraindicated in patients receiving terfenadine.
Source: DDInter
Arsenic Trioxide
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Other Antihistamine drugs
Ask House about terfenadine
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Goodman & Gilman 14e·Verified: 2026-05-10 · House clinical team