What is the protocol for transitioning from a Cardizem (Diltiazem) intravenous drip to oral administration?

From the Guidelines

When transitioning from a Cardizem (diltiazem) drip to oral therapy, start with oral diltiazem at a dose of 120-360 mg daily in divided doses, with the total daily dose approximately equivalent to the 24-hour IV dose, as recommended by the most recent guidelines 1. The transition should occur once the patient is hemodynamically stable with controlled heart rate or blood pressure.

• Key considerations for the transition include:
  • Oral bioavailability is approximately 40-60% of IV dosing
  • The first oral dose should be given 1-2 hours before discontinuing the IV infusion to ensure therapeutic levels are maintained
  • Monitor vital signs closely during the transition, especially heart rate and blood pressure
  • Adjust the oral dose as needed based on the patient's clinical response over the first 24-48 hours after conversion
• The most recent guidelines recommend diltiazem as a first-line agent for rate control in atrial fibrillation, with a recommended oral maintenance dose of 120-360 mg daily in divided doses 1.
• It is essential to note that diltiazem should be avoided in patients with heart failure with reduced ejection fraction (HFrEF) due to its negative inotropic effects, as stated in the guidelines 1.
• In patients with HFrEF, alternative agents such as beta-blockers or digoxin may be considered for rate control, as recommended by the guidelines 1.
• The guidelines also emphasize the importance of individualizing treatment and monitoring patients closely during the transition from IV to oral therapy 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.

When transitioning from a Cardizem drip to oral diltiazem, the patient's dose should be adjusted to account for the bioavailability difference between intravenous and oral administration.

• The oral dose may need to be higher than the intravenous dose due to the first-pass effect.
• It is recommended to monitor the patient's plasma levels and adjust the dose accordingly to achieve the desired therapeutic effect.
• The time to reach peak plasma levels after oral administration is 2 to 4 hours, which should be considered when transitioning from intravenous to oral therapy 2.

From the Research

Transitioning to Cardizem Drip to Oral

• The process of transitioning from intravenous to oral diltiazem, also known as Cardizem, has been studied in various research papers 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 atrial fibrillation or flutter who were initially controlled with intravenous diltiazem 3.
• Another study published in 2018 compared the incidence of treatment failure between oral immediate-release and intravenous continuous infusion diltiazem after an initial intravenous diltiazem loading dose, and found that oral immediate-release diltiazem was associated with a lower rate of treatment failure at four hours 4.

Comparison with Other Medications

• Research has also compared the efficacy and safety of diltiazem with other medications, such as metoprolol, for rate control in atrial fibrillation 5, 6, 7.
• A study published in 2021 found that there was no statistically significant difference between diltiazem, metoprolol, and verapamil in achieving rate control in patients with atrial fibrillation with rapid ventricular rate 5.
• A systematic review and meta-analysis published in 2024 found that metoprolol was associated with a 26% lower risk of adverse events compared to diltiazem for atrial fibrillation with rapid ventricular rate 7.

Key Findings

• The median infusion rate of intravenous diltiazem was 10 mg/hour, and the median dose of oral diltiazem was 300 mg/day 3.
• Oral immediate-release diltiazem was associated with a lower rate of treatment failure at four hours compared to intravenous continuous infusion diltiazem 4.
• There was no difference in the achievement of rate control between intravenous metoprolol and diltiazem 6.