May exacerbate QT prolongation by heart rate reduction w/ CV (eg, quinidine, disopyramide, bepridil, sotalol, ibutilide, amiodarone) & non-CV (eg, pimozide, ziprasidone, sertindole, mefloquine, halofantrine, pentamidine, cisapride, IV erythromycin) QT prolonging medicinal products. Increased risk of arrhythmia w/ K-depleting diuretics (eg, thiazide & loop diuretics). Increased plasma conc w/ CYP3A4 inhibitors. Decreased plasma conc w/ CYP3A4 inducers. Increased mean plasma exposure w/ potent CYP3A4 inhibitors (eg, ketoconazole & josamycin). Increased exposure & additional heart rate reduction w/ diltiazem or verapamil. 2-fold increase in exposure w/ grapefruit juice. Concomitant use w/ moderate CYP3A4 inhibitors (eg, fluconazole). May decreased exposure & activity w/ CYP3A4 inducers (eg, rifampicin, barbiturates, phenytoin,
Hypericum perforatum [St John's Wort]).