Drug-induced QT interval prolongation after ciprofloxacin administration in a patient receiving olanzapine.

Several non-antiarrhythmic drugs including antibiotic and antipsychotic agents have been shown to prolong cardiac repolarization predisposing to torsade de pointes ventricular tachycardia. Blockade of the delayed rectifier (repolarising) potassium current and drug interactions with inhibitors of the CYP-mediated metabolism are the most common underlying mechanisms. In the present case report, an elderly woman receiving a long-term medication with azathioprine, olanzapine and valsartan developed a marked QT interval prolongation after intravenous administration of ciprofloxacin.