Amiodarone × Diltiazem

Both drugs slow the heart rate and conduction; together they can cause excessive bradycardia, sinus arrest and atrioventricular (AV) block (amiodarone labels in Spain and the US). There is also a pharmacokinetic part: CYP3A4 takes part in amiodarone metabolism and diltiazem moderately inhibits it. The Spanish amiodarone label advises avoiding CYP3A4 inhibitors because they can raise amiodarone levels, and the diltiazem label does not rule out higher diltiazem levels with amiodarone. Because of amiodarone's long half-life, interactions persist for weeks to months after it is stopped (amiodarone labels).

Slow pulse, sinus arrest and atrioventricular (AV) block (FDA amiodarone label). A slow pulse causes weakness and dizziness, and in severe cases fainting. The risk of bradycardia is higher in older patients and at high doses (diltiazem label).

The Spanish amiodarone label does not recommend combining it with diltiazem because of the risk of excessive bradycardia and conduction disorders (amiodarone label). The Spanish diltiazem label requires strict clinical and ECG monitoring when it is combined with other antiarrhythmics, and caution with amiodarone, especially in older patients and at high doses (diltiazem label). If the combination cannot be avoided, adjust doses carefully and monitor heart rate (FDA amiodarone label) and the ECG (diltiazem label). Amiodarone interactions persist for weeks to months after it is stopped, so the same caution applies if diltiazem is started soon after amiodarone is withdrawn (amiodarone labels).