Q: Please let me know if azithromycin has any drug interaction with fexofenadine.

A:Azithromycin (brand names: Aziwok, Azithral) being a macrolide antibiotic issimilar to erythromycin. Fexofenadine (brand names: Alernex, Allegra) is a pharmacologically active metabolite of terfenadine.

It is known that erythromycin increases the serum levels of fexofenadine by 82%. The AUC goes up by 109%. Unlike terfenadine (discarded the world over for unacceptable, life-threatening adverse effects), concurrent use of erythormycin with fexofenadine does not have any effect on QTc interval on the ECG and is not cardiotoxic. This is probably so because fexofenadine does not undergo hepatic biotransformation.

Indications from studies suggest that in all likelihood other macrolide antibiotics (such as azithromycin, clarithromycin - Clarimac,roxithromycin - Unorox) also can be given safely with fexofenadine.