Some of the
azoles raise
astemizole and
terfenadine levels, which may increase the risk of serious life-threatening arrhythmias. Cases of torsade de pointes have been reported when
astemizole is given with
ketoconazole, and when
terfenadine is given with
itraconazole or
ketoconazole. An arrhythmia has also been reported in a patient taking
terfenadine and using topical oxiconazole. Ketoconazole raises
mizolastine levels, which caused a small increase in the QT interval in one study.
The manufacturers of astemizole,
mizolastine and
terfenadine contraindicate the concurrent use of
azoles and the manufacturer of
terfenadine extends this
contraindication to the concurrent use of topical
azoles.