An additive effect on QT interval prolongation of moxifloxacin and other medicinal products that may prolong the QTc interval cannot be excluded. This might lead to an increased risk of ventricular arrhythmias, including torsade de pointes. Therefore, co-administration of moxifloxacin with any of the following medicinal products is contraindicated: anti-arrhythmics class IA (e.g. quinidine, hydroquinidine, disopyramide); anti-arrhythmics class III (e.g. amiodarone, sotalol, dofetilide, ibutilide); antipsychotics (e.g. phenothiazines, pimozide, sertindole, haloperidol, sultopride); tricyclic antidepressive agents; certain antimicrobial agents (saquinavir, sparfloxacin, erythromycin IV, pentamidine, antimalarials particularly halofantrine); certain antihistaminics (terfenadine, astemizole, mizolastine); others (cisapride, vincamine IV, bepridil, diphemanil).
Moxifloxacin should be used with caution in patients who are taking medication that can reduce potassium levels (e.g. loop and thiazide-type diuretics, laxatives and enemas [high doses], corticosteroids, amphotericin B) or medication that is associated with clinically significant bradycardia.
An interval of about 6 hours should be left between administration of agents containing bivalent or trivalent cations (e.g. antacids containing magnesium or aluminium, didanosine tablets, sucralfate and agents containing iron or zinc) and administration of moxifloxacin.
Concomitant administration of charcoal with an oral dose of 400 mg moxifloxacin led to a pronounced prevention of drug absorption and a reduced systemic availability of the drug by more than 80%. Therefore, the concomitant use of these two drugs is not recommended.
A large number of cases showing an increase in oral anticoagulant activity have been reported in patients receiving antibacterial agents. A precautionary measure would be to more frequently monitor the INR. If necessary, the oral anticoagulant dosage should be adjusted as appropriate.