Haloperidol × Moxifloxacin

Both drugs prolong the QT interval on the electrocardiogram. The haloperidol SmPC reports QT prolongation, ventricular arrhythmias and sudden death; the risk is higher with high doses, high plasma levels and parenteral use, especially intravenous. Moxifloxacin prolongs QT more as its concentration rises, and its SmPC does not exclude an additive effect with other QT-prolonging drugs (moxifloxacin SmPC). Together they raise the risk of torsades de pointes.

QT prolongation on the electrocardiogram (ECG) causes no symptoms by itself. Palpitations, dizziness or fainting may occur. The dangerous complication is torsades de pointes, a ventricular tachycardia that can lead to cardiac arrest (moxifloxacin SmPC). The risk is higher in women and older people, with low potassium or magnesium, marked bradycardia or heart disease (moxifloxacin and haloperidol SmPCs).

Both Spanish SmPCs contraindicate this combination. The haloperidol SmPC contraindicates haloperidol with drugs that prolong the QT interval and names moxifloxacin, and the moxifloxacin SmPC contraindicates moxifloxacin with antipsychotics and names haloperidol. The moxifloxacin label approved by the US Food and Drug Administration (FDA) advises avoiding it with antipsychotics (moxifloxacin FDA label). The haloperidol SmPC also contraindicates other antibiotics from the same groups: levofloxacin, azithromycin, clarithromycin, erythromycin. Before haloperidol is started, an electrocardiogram (ECG) is recorded and low potassium and magnesium are corrected; if the corrected QT interval (QTc) lengthens, the haloperidol dose is reduced, and haloperidol is stopped if QTc exceeds 500 ms (haloperidol SmPC). If signs of arrhythmia appear on moxifloxacin, it is stopped and an ECG is recorded; the recommended dose is not exceeded (moxifloxacin SmPC).