What is the oral (PO) equivalent of diltiazem 20 mg intravenous (IV) push?

Oral Equivalent of Diltiazem 20 mg IV Push

After an initial IV bolus of 20 mg diltiazem (0.25 mg/kg), transition to oral immediate-release diltiazem 30 mg every 6-8 hours or 120 mg daily of an extended-release formulation for ongoing rate control. 1

Conversion Rationale

The conversion from IV to oral diltiazem is not a simple 1:1 ratio due to significant first-pass metabolism:

• Oral bioavailability of immediate-release diltiazem is approximately 40% compared to IV administration, meaning oral doses must be substantially higher to achieve equivalent plasma concentrations 2
• After a 20 mg IV bolus (which provides immediate therapeutic effect), the standard approach is to initiate oral maintenance dosing at 120-360 mg daily rather than attempting to calculate an exact equivalent 1

Recommended Transition Strategy

For Acute Rate Control (e.g., Atrial Fibrillation with RVR):

• Initial IV bolus: 0.25 mg/kg (approximately 20 mg for average adult) over 2 minutes 1, 3
• If additional control needed: May repeat with 0.35 mg/kg (approximately 25 mg) after 15 minutes 1
• Transition to oral: Start immediate-release diltiazem 30 mg PO every 6-8 hours OR extended-release 120-180 mg once daily 4, 5

Clinical Evidence for Oral Dosing:

Immediate-release formulation (30-60 mg every 6-8 hours) has been shown to be more effective than IV continuous infusion for sustained rate control after initial IV loading, with lower treatment failure rates (27% vs 46%) 5

Dosing Considerations

Immediate-Release Formulation:

• Starting dose: 30 mg every 6-8 hours (120 mg/day total) 2
• Titration: Can increase to 60 mg every 6-8 hours (240 mg/day) based on response 1
• Peak effect: 2-4 hours after administration 2
• Half-life: 3.0-4.5 hours 2

Extended-Release Formulation:

• Starting dose: 120-180 mg once daily 4
• Maximum dose: 360-420 mg once daily 4
• Advantage: Maintains stable plasma concentrations over 24 hours 4

Important Caveats

Avoid Oral Diltiazem in:

• AV block greater than first degree or SA node dysfunction without pacemaker 1, 3
• Decompensated systolic heart failure or severe LV dysfunction 1, 3
• Wolff-Parkinson-White syndrome with atrial fibrillation/flutter 1, 3
• Cardiogenic shock or severe hypotension 1

Monitor for:

• Hypotension (most common adverse effect) 1, 3
• Bradycardia (may be dose-limiting) 1
• Worsening heart failure in predisposed patients 1, 3

Drug Interactions:

• Diltiazem is a CYP3A4 substrate and moderate inhibitor, requiring caution with apixaban, cyclosporine, simvastatin, and other CYP3A4 substrates 1, 4
• Avoid combining with other AV nodal blocking agents (beta-blockers, digoxin) without careful monitoring 1

Practical Algorithm

1. Give IV bolus 0.25 mg/kg (≈20 mg) over 2 minutes 1, 3
2. Assess response at 15 minutes: If HR remains >110 bpm, may give second bolus 0.35 mg/kg 1
3. For ongoing control, choose ONE of:
   • Immediate-release: 30 mg PO q6-8h (preferred if patient may be discharged) 5
   • Extended-release: 120-180 mg PO once daily (preferred for compliance) 4
   • IV infusion: 5-15 mg/hr (only if patient cannot take oral medications) 1

The median effective oral dose after IV loading is 30 mg of immediate-release formulation, which provides superior sustained rate control compared to IV infusion in the emergency setting 5