Additive effect on QT interval prolongation w/ other medicinal products that may prolong the QTc interval eg, class IA (eg, quinidine, hydroquinidine, disopyramide) & III (eg, amiodarone, sotalol, dofetilide, ibutilide) anti-arrhythmics, antipsychotics (eg, phenothiazines, pimozide, sertindole, haloperidol, sultopride), TCAs, certain antimicrobial agents (eg, saquinavir, sparfloxacin, erythromycin IV, pentamidine, antimalarials particularly halofantrine), certain antihistaminics (eg, terfenadine, astemizole, mizolastine) & cisapride, vincamine IV, bepridil, diphemanil.