Can I administer Cardizem (Diltiazem) and Metoprolol simultaneously?

From the Guidelines

Cardizem (diltiazem) and metoprolol should generally not be given together due to the risk of additive effects that can cause excessive heart rate lowering, blood pressure reduction, and potential heart block. Both medications are used to treat cardiovascular conditions but work through different mechanisms that, when combined, can dangerously slow heart function. This combination may be prescribed in specific circumstances by a cardiologist with careful monitoring, but it's not standard practice. If you're currently taking one of these medications and have been prescribed the other, consult your healthcare provider immediately before taking both. The concern stems from their complementary actions - metoprolol blocks beta receptors while diltiazem blocks calcium channels, both ultimately reducing heart rate and contractility. Alternative combinations or single-drug approaches are typically preferred to achieve cardiovascular control without the heightened risk of bradycardia or heart block, as suggested by the guidelines for the management of adult patients with supraventricular tachycardia 1. Some key points to consider when deciding on the use of these medications together include:

• The potential for hypotension, bronchospasm, and bradycardia with metoprolol, as well as the precautions against using it in patients with AV block greater than first degree or SA node dysfunction, decompensated systolic heart failure, hypotension, reactive airway disease, or severe renal dysfunction 1.
• The potential for hypotension, worsening heart failure, bradycardia, and abnormal liver function studies with diltiazem, as well as the precautions against using it in patients with AV block greater than first degree or SA node dysfunction, hypotension, decompensated systolic heart failure, or drugs with SA and/or AV nodal-blocking properties 1. Given the potential risks, it is crucial to weigh the benefits against the risks and consider alternative treatment options that do not involve combining these two medications, unless under the close supervision of a cardiologist, as indicated by various guidelines for the management of patients with atrial fibrillation 1.

From the FDA Drug Label

Pharmacologic studies indicate that there may be additive effects in prolonging AV conduction when using beta-blockers or digitalis concomitantly with diltiazem hydrochloride Controlled and uncontrolled domestic studies suggest that concomitant use of diltiazem hydrochloride and beta-blockers is usually well tolerated Administration of diltiazem hydrochloride concomitantly with propranolol in five normal volunteers resulted in increased propranolol levels in all subjects, and bioavailability of propranolol was increased approximately 50%.

• Concomitant use of diltiazem and beta-blockers: The FDA drug label suggests that concomitant use of diltiazem and beta-blockers, such as metoprolol, may be usually well tolerated, but caution is advised due to potential additive effects on AV conduction.
• Dose adjustment: The label recommends that dose adjustments may be necessary when initiating or stopping concomitant administration of diltiazem and beta-blockers, such as metoprolol.
• Monitoring: It is recommended to monitor patients closely for potential adverse effects, such as bradycardia or conduction disturbances, when using diltiazem and metoprolol concomitantly 2.

From the Research

Comparison of Cardizem (Diltiazem) and Metoprolol

• Both Cardizem (diltiazem) and metoprolol are used to treat atrial fibrillation with rapid ventricular response (RVR) and have been compared in several studies for their effectiveness and safety 3, 4, 5, 6, 7.
• A study published in 2022 found that diltiazem and metoprolol had similar safety and effectiveness outcomes in patients with atrial fibrillation and heart failure, but diltiazem reduced heart rate more quickly and effectively 3.
• Another study published in 2021 found that there was no significant difference in rate control between diltiazem and metoprolol, but diltiazem resulted in a greater decrease in heart rate at 0.5 hours and a higher incidence of hypotension 4.
• A 2015 study found that diltiazem was more effective in achieving rate control in patients with atrial fibrillation or flutter with RVR, with no increased incidence of adverse effects 5.
• A systematic review and meta-analysis published in 2024 found that metoprolol was associated with a lower risk of adverse events compared to diltiazem, but there was no difference in rates of bradycardia or hypotension 6.
• A 2019 study found that diltiazem and metoprolol had similar effects in the acute management of atrial fibrillation with RVR in patients with heart failure with reduced ejection fraction, with no increase in adverse events with diltiazem 7.

Safety and Efficacy

• The safety and efficacy of diltiazem and metoprolol have been evaluated in several studies, with varying results 3, 4, 5, 6, 7.
• Diltiazem has been found to be effective in reducing heart rate and achieving rate control in patients with atrial fibrillation or flutter with RVR, but may be associated with a higher incidence of hypotension 4, 5.
• Metoprolol has been found to be associated with a lower risk of adverse events compared to diltiazem, but may not be as effective in reducing heart rate in some patients 6.

Clinical Use

• The choice between diltiazem and metoprolol for the treatment of atrial fibrillation with RVR should be based on individual patient factors and clinical judgment 3, 4, 5, 6, 7.
• Patients with heart failure or other comorbidities may require careful consideration of the potential risks and benefits of each medication 3, 7.