Erythromycin causes terfenadine and astemizole to accumulate in a few individuals, which can prolong the QT interval and lead to life-threatening torsade de pointes arrhythmias. Cases of torsade de pointes have been reported for astemizole with
erythromycin, and terfenadine with
erythromycin. Other
macrolides are believed to interact similarly, with the exception of
azithromycin and possibly
dirithromycin. Erythromycin modestly raises mizolastine levels, although this has no effect on the QT interval. Erythromycin markedly raises ebastine levels, which caused a modest prolongation of the QT interval in one study. Consider also drugs that prolong the QT interval.
The manufacturers of astemizole, ebastine, mizolastine and terfenadine con- traindicate their use with all
macrolides, with the isolated exception of astemizole with
azithromycin. The manufacturer of terfenadine extends this
contraindication to the concurrent use of topical
macrolides. Azelastine,
cetirizine,
desloratadine,
fexofenadine and intranasal levocabastine may be suitable non-interacting alternatives. Note that the
macrolides differ in the likely extent of their interaction, see
macrolides.