What is the protocol for transitioning from intravenous (IV) diltiazem (Cardizem) to oral rate control in atrial fibrillation (AFib)?

From the Guidelines

When transitioning from IV diltiazem to oral rate control in atrial fibrillation, start oral diltiazem 1-2 hours before discontinuing the IV infusion, beginning with diltiazem extended-release 120-240 mg daily or immediate-release 30-60 mg four times daily, adjusting based on the effective IV dose, as recommended by the 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation 1. The most recent and highest quality study, the 2014 AHA/ACC/HRS guideline, provides the best evidence for this recommendation. Some key points to consider when making this transition include:

• Monitoring heart rate and blood pressure during the transition, aiming for a resting heart rate of 60-100 beats per minute 1
• Alternative oral options, such as metoprolol (25-100 mg twice daily), carvedilol (3.125-25 mg twice daily), or non-dihydropyridine calcium channel blockers like verapamil, may be considered 1
• Patients with severe heart failure, hypotension, or significant conduction abnormalities may require more cautious dosing or alternative strategies 1
• Ensuring adequate anticoagulation is maintained throughout the transition period, as rate control does not reduce stroke risk in atrial fibrillation 1 It's also important to note that the 2006 ACC/AHA/ESC guidelines for the management of patients with atrial fibrillation provide similar recommendations, but the 2014 guideline is more recent and takes precedence 1.

From the FDA Drug Label

Diltiazem is well absorbed from the gastrointestinal tract and is subject to an extensive first-pass effect, giving an absolute bioavailability (compared to intravenous dosing) of about 40%. Single oral doses of 30 to 120 mg of diltiazem hydrochloride tablets result in detectable plasma levels within 30 to 60 minutes and peak plasma levels 2 to 4 hours after drug administration.

To transition from IV diltiazem to oral rate control in AFib, consider the following:

• Bioavailability: The oral bioavailability of diltiazem is about 40% compared to IV dosing.
• Dosing: The oral dose of diltiazem can be adjusted to achieve the desired therapeutic effect, with peak plasma levels reached 2 to 4 hours after administration.
• Monitoring: Monitor the patient's heart rate and rhythm closely during the transition from IV to oral diltiazem, as the oral formulation may have a slower onset of action.
• Key considerations:
  • The IV dose may need to be adjusted before transitioning to oral to ensure a smooth transition.
  • The patient's renal and hepatic function should be considered when determining the oral dose, as these factors can affect the pharmacokinetics of diltiazem 2.

From the Research

Transition from IV Diltiazem to Oral Rate Control in AFib

• The transition from intravenous (IV) diltiazem to oral diltiazem for rate control in atrial fibrillation (AFib) has been studied in various clinical trials 3, 4.
• A study published in 1996 found that oral long-acting diltiazem was 77% effective in controlling ventricular response over 48 hours in patients with AFib or atrial flutter who were initially controlled with IV diltiazem 3.
• Another study published in 2018 compared the incidence of treatment failure between oral immediate-release and IV continuous infusion diltiazem after an initial IV diltiazem loading dose, and found that oral immediate-release diltiazem was associated with a lower rate of treatment failure at four hours 4.

Dosing Strategies for Diltiazem in AFib

• The optimal dosing strategy for diltiazem in AFib is still a topic of debate, with some studies suggesting that a weight-based dosing approach may be more effective 5.
• A study published in 2021 found that patients who received a diltiazem bolus dose of ≥ 0.13 mg/kg achieved heart rate control more quickly and had a higher rate of heart rate control compared to those who received a lower dose 5.

Comparison with Other Rate Control Agents

• Diltiazem has been compared to other rate control agents, such as metoprolol, in several studies 6, 7.
• A study published in 2015 found that diltiazem was more effective than metoprolol in achieving rate control in patients with AFib or atrial flutter 6.
• 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 found no difference in rates of hypotension or bradycardia 7.