Azithromycin × Haloperidol

Both drugs prolong the QT interval on the electrocardiogram. The azithromycin SmPC reports QT prolongation and torsades de pointes with macrolides, azithromycin included. 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. Together the effects add up.

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 end in cardiac arrest (azithromycin SmPC). The risk is higher in women and older people, with low potassium or magnesium, marked bradycardia, heart disease or severe heart failure (azithromycin and haloperidol SmPCs).

The combination is contraindicated: the Spanish haloperidol SmPC contraindicates haloperidol with drugs that prolong the QT interval and names azithromycin among them (haloperidol SmPC). The azithromycin SmPC asks for caution with such drugs, antipsychotics included (azithromycin SmPC), and the azithromycin label approved by the US Food and Drug Administration (FDA) advises weighing the risk of fatal QT prolongation in patients who take them (azithromycin FDA label). 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).