Which medication has a greater effect on heart rate, amiodarone or metoprolol?

From the Guidelines

Metoprolol has a greater effect on heart rate compared to amiodarone. Metoprolol, a beta-blocker, directly slows heart rate by blocking the effects of adrenaline and noradrenaline on the heart, typically reducing heart rate by 10-20 beats per minute at standard doses (25-100 mg twice daily for immediate release or 50-200 mg once daily for extended release) 1. Amiodarone, while it can affect heart rate, primarily works by altering the electrical properties of heart tissue, with a less pronounced and more variable effect on heart rate compared to metoprolol 1. Some key points to consider when choosing between these medications include:

• The specific cardiac condition being treated, as they have different primary indications and side effect profiles
• The need for immediate heart rate control, for which metoprolol would be preferred
• The potential for extracardiac side-effects with amiodarone, especially on long-term therapy 1
• The complex effects of amiodarone involving multiple ion channels and a longer onset of action, making metoprolol a more straightforward choice for heart rate control 1. Overall, when considering the impact on heart rate, metoprolol is the more effective option due to its direct action on beta-1 receptors in the heart.

From the Research

Comparison of Amiodarone and Metoprolol Effects on Heart Rate

• Amiodarone and metoprolol are both used to treat cardiac arrhythmias, but their effects on heart rate can differ due to their distinct mechanisms of action and potential interactions 2, 3.
• Studies have shown that amiodarone can increase metoprolol concentrations by inhibiting the cytochrome P450 2D6 enzyme, leading to a higher risk of bradycardia and atrioventricular block 2, 3.
• The combination of amiodarone and metoprolol has been found to have a greater effect on reducing heart rate compared to metoprolol alone, with one study showing a significant decrease in mean ventricular rate in patients treated with amiodarone and metoprolol compared to those treated with metoprolol alone 4.
• Another study found that amiodarone had a more significant effect on reducing heart rate and improving cardiac function compared to metoprolol in patients with heart failure and persistent atrial fibrillation 4.

Key Findings

• Amiodarone use was associated with higher metoprolol concentrations and lower heart rates in patients with cardiac arrhythmias 2.
• The combination of amiodarone and metoprolol resulted in significant cardiac function improvement and ventricular arrhythmia control compared to either drug alone 5.
• Amiodarone had a more significant effect on reducing heart rate and improving cardiac function compared to metoprolol in patients with heart failure and persistent atrial fibrillation 4.
• The acute effects of the metoprolol/amiodarone combination in isolated rat hearts showed no myocardial contractility depression or bradycardia accentuation compared to metoprolol alone, but increased coronary flow 6.

Interaction Between Amiodarone and Metoprolol

• The interaction between amiodarone and metoprolol is complex and can lead to increased metoprolol concentrations and a higher risk of bradycardia and atrioventricular block 2, 3.
• The combination of amiodarone and metoprolol can have a greater effect on reducing heart rate and improving cardiac function compared to either drug alone, but careful monitoring of metoprolol concentrations and heart rate is required 2, 3, 4.