From the Guidelines
For rate control in addition to amiodarone and metoprolol, I recommend adding diltiazem, starting at 120-360 mg daily in divided doses of the extended-release formulation. This calcium channel blocker works through a different mechanism than your current medications, providing complementary rate control by slowing conduction through the AV node 1. When adding diltiazem, monitor blood pressure closely as the combination with metoprolol may cause excessive hypotension. Start at a lower dose (120 mg daily) if the patient has hepatic impairment, is elderly, or has borderline blood pressure. Regular ECG monitoring is essential to assess the QT interval, as both amiodarone and diltiazem can prolong it 1. If hypotension becomes problematic, consider reducing the metoprolol dose rather than immediately discontinuing diltiazem. Digoxin could be an alternative if diltiazem is not tolerated, but it has more drug interactions with amiodarone and requires careful serum level monitoring 1.
Some key points to consider when using diltiazem include:
- Avoid using diltiazem in patients with heart failure with reduced ejection fraction (HFrEF) 1
- Monitor for signs of hypotension, heart block, and bradycardia 1
- Be aware of potential drug interactions, particularly with amiodarone and digoxin 1
- Regularly assess the patient's renal function, as diltiazem is primarily eliminated through the liver, but its active metabolites are renally eliminated 1
Overall, the addition of diltiazem to amiodarone and metoprolol can provide effective rate control in patients with atrial fibrillation, but requires careful monitoring and dose adjustment to minimize potential adverse effects 1.
From the FDA Drug Label
Amiodarone should be used with caution in patients receiving ß- receptor blocking agents (e.g., propranolol, a CYP3A4 inhibitor) or calcium channel antagonists (e.g., verapamil, a CYP3A4 substrate, and diltiazem, a CYP3A4 inhibitor) because of the possible potentiation of bradycardia, sinus arrest, and AV block; if necessary, amiodarone can continue to be used after insertion of a pacemaker in patients with severe bradycardia or sinus arrest In amiodarone-treated patients who require additional antiarrhythmic therapy, the initial dose of such agents should be approximately half of the usual recommended dose.
The patient is already on metoprolol, which is a ß-receptor blocking agent. When adding another rate control medication to amiodarone and metoprolol, consider the potential for increased risk of bradycardia, sinus arrest, and AV block. Diltiazem or verapamil should be used with caution due to potential interactions with amiodarone. Consider alternative rate control medications that do not have significant interactions with amiodarone and metoprolol, such as digoxin (with careful monitoring of serum levels) or other medications not listed in the provided drug labels. However, the FDA label does not provide a clear recommendation for a specific rate control medication to add to amiodarone and metoprolol. Therefore, the choice of medication should be based on individual patient needs and careful consideration of potential interactions. 2 2
From the Research
Rate Control Medications
To add to amiodarone and metoprolol for rate control, the following options can be considered:
- Digoxin: can be useful in combination with a beta blocker or nondihydropyridine calcium channel blocker to achieve adequate rate control 3
- Diltiazem: a calcium channel blocker that can achieve rate control faster than metoprolol, and is safe and effective 4
- Verapamil: a calcium channel blocker that can be used for rate control, especially in patients who cannot tolerate beta blockers 5
Considerations
When selecting a rate control medication, it is essential to consider the individual patient's clinical situation, comorbidities, and potential interactions with other medications, such as amiodarone 6. The goal of rate control is to achieve a resting heart rate less than 110 beats per minute, with rates below 90 beats per minute being preferable 3.
Combination Therapy
Combining rate control medications, such as beta blockers and nondihydropyridine calcium channel blockers, can be effective in achieving adequate rate control 3. Additionally, digoxin can be useful as primary therapy in patients with hypotension or heart failure 3.