Which antihistamine should NOT be taken with erythromycin?

Which antihistamine should NOT be taken with erythromycin?

• A. Loratadine
• B. Cetirizine
• C. Fexofenadine
• D. Terfenadine

Answer: (D)

The risk here comes from how erythromycin affects drug metabolism. Erythromycin inhibits the liver enzyme CYP3A4. Terfenadine relies on this enzyme to be broken down; when CYP3A4 is blocked, terfenadine builds up in the blood and can prolong the heart’s QT interval, potentially leading to dangerous arrhythmias. Because of this interaction, terfenadine should not be taken with erythromycin. Other antihistamines listed are not as dependent on CYP3A4 for clearance or don’t significantly raise QT risk with this antibiotic, so they don’t carry the same interaction concern with erythromycin.

The risk here comes from how erythromycin affects drug metabolism. Erythromycin inhibits the liver enzyme CYP3A4. Terfenadine relies on this enzyme to be broken down; when CYP3A4 is blocked, terfenadine builds up in the blood and can prolong the heart’s QT interval, potentially leading to dangerous arrhythmias. Because of this interaction, terfenadine should not be taken with erythromycin.

Other antihistamines listed are not as dependent on CYP3A4 for clearance or don’t significantly raise QT risk with this antibiotic, so they don’t carry the same interaction concern with erythromycin.