From the Guidelines
When converting from Cardizem (diltiazem) intravenous drip at 5 mg/hour to oral therapy, the recommended approach is to start with oral diltiazem 60-120 mg three times daily (total daily dose of 180-360 mg) 1. This conversion is not a direct milligram-to-milligram switch because oral diltiazem has lower bioavailability (approximately 40-60%) compared to the intravenous form. The first oral dose should be given 3-6 hours before discontinuing the IV infusion to ensure adequate blood levels are maintained during the transition. After starting oral therapy, the patient should be monitored for blood pressure, heart rate, and symptom control to ensure the oral dose is effective. Dose adjustments may be necessary based on the patient's response. For patients with hepatic or renal impairment, consider starting with a lower dose of 30 mg three times daily. Extended-release formulations are also available (120-360 mg once daily), which may improve compliance, but these should typically be initiated after stabilization on the immediate-release formulation. The conversion is necessary because IV diltiazem is intended for short-term use, while oral therapy is more appropriate for ongoing management of conditions like hypertension, angina, or atrial fibrillation. Key considerations include:
- Monitoring for potential adverse effects such as hypotension, bradycardia, and worsening heart failure
- Adjusting doses based on patient response and comorbid conditions
- Being aware of potential drug interactions, especially with other medications that affect the AV node or have similar side effects. Given the most recent and highest quality evidence from 1 and 1, these guidelines provide the best approach for converting IV diltiazem to oral therapy, prioritizing patient safety and effective management of underlying conditions.
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%.
The oral equivalent of Cardizem (Diltiazem) 5mg given intravenously is approximately 12.5mg, considering the absolute bioavailability of about 40% 2.
From the Research
Oral Equivalent of Cardizem (Diltiazem) 5mg Given Intravenously
To determine the oral equivalent of Cardizem (Diltiazem) 5mg given intravenously, we need to consider the pharmacokinetics and bioavailability of diltiazem.
- The study 3 compared the effectiveness of oral long-acting diltiazem with intravenous diltiazem in patients with atrial fibrillation or flutter, but it did not provide a direct comparison of the oral equivalent of a 5mg intravenous dose.
- Another study 4 compared oral immediate-release diltiazem with intravenous continuous infusion diltiazem in patients with atrial fibrillation and rapid ventricular response, and found that the median dose of oral diltiazem was 30 mg, while the median infusion rate of intravenous diltiazem was 10 mg/hour.
- A pharmacokinetic study 5 examined the steady-state pharmacokinetics of high-dose diltiazem hydrochloride (Cardizem CD) administered once daily in healthy volunteers, but it did not provide information on the oral equivalent of a specific intravenous dose.
- Other studies 6, 7 discussed the clinical experience and effects of diltiazem in treating hypertension and supraventricular tachycardia, but did not provide direct information on the oral equivalent of a 5mg intravenous dose.
Key Findings
- The oral bioavailability of diltiazem is approximately 40% 5, which means that the oral dose required to achieve the same effect as an intravenous dose may be higher.
- The study 4 suggests that an oral dose of 30 mg may be equivalent to an intravenous infusion rate of 10 mg/hour, but this does not directly translate to a 5mg intravenous dose.
- Based on the available data, it is difficult to determine the exact oral equivalent of a 5mg intravenous dose of Cardizem (Diltiazem), and further studies are needed to provide a definitive answer.