Amiodarone × Quetiapine

Both drugs prolong the QT interval. For amiodarone this is part of its main action: PR and QT intervals lengthen by about 10% (amiodarone label, US Food and Drug Administration, FDA). After quetiapine reached the market, QT prolongation was reported at therapeutic doses and in overdose (quetiapine SmPC). Together they raise the risk of torsades de pointes. Quetiapine is also cleared mainly by CYP3A4 (quetiapine SmPC), which amiodarone inhibits (amiodarone SmPC), so quetiapine levels may rise.

QT prolongation on ECG. Dizziness, syncope, palpitations. Severe cases: polymorphic ventricular tachycardia (torsades de pointes). Risk is higher with hypokalaemia and hypomagnesaemia.

The combination is avoided: the quetiapine label approved by the US Food and Drug Administration (FDA) names amiodarone among QT-prolonging drugs whose combination with quetiapine should be avoided, and the FDA amiodarone label advises against combining it with QT-prolonging drugs. The Spanish amiodarone SmPC allows the combination only after a careful benefit-risk assessment for the individual patient and with QT monitoring (amiodarone SmPC). Low potassium increases QT prolongation on amiodarone, so a potassium deficit is corrected (amiodarone SmPC). Quetiapine needs particular caution in older patients and in congenital long QT syndrome, heart failure, cardiac hypertrophy, low potassium or low magnesium (quetiapine SmPC). Amiodarone interactions can persist for several months after it is stopped (amiodarone SmPC).