Additive effect on QT interval prolongation w/ anti-arrhythmics class IA (eg, quinidine, hydroquinidine, disopyramide), anti-arrhythmics class III (eg, amiodarone, sotalol, dofetilide, ibutilide), antipsychotics (eg, phenothiazines, pimozide, sertindole, haloperidol, sultopride), TCAs, certain antimicrobials (saquinavir, sparfloxacin, erythromycin IV, pentamidine, antimalarials particularly halofantrine), certain antihistaminics (terfenadine, astemizole, mizolastine), cisapride, vincamine IV, bepridil, diphemanil. Caution in concomitant use w/ K level reducing drugs [eg, loop & thiazide-type diuretics, laxatives & enemas (high doses), corticosteroids, amphotericin B] or drugs associated w/ clinically significant bradycardia. Absorption may be impaired w/ bivalent or trivalent cation-containing agents (eg, Mg- & Al-containing antacids, didanosine tab, sucralfate & Fe- or Zn-containing agents). Pronounced prevention of absorption & reduced systemic availability w/ charcoal. May increase oral anticoagulant activity.