Increased risk of ventricular arrhythmias including Torsade de pointes w/ class IA & III antiarrhythmics, antipsychotics, TCAs, certain antimicrobials & antihistamines, cisapride, vincamine IV, bepridil, diphemanil. Impaired absorption w/ antacids, minerals, multivit, antiretroviral drugs eg, didanosine, Mg-, Al-, Fe- or Zn-containing prep, sucralfate. Increased anticoagulant activity. Reduced systemic availability w/ charcoal. Caution w/ loop & thiazide diuretics, high-dose laxatives & enemas, corticosteroids, amphotericin B.