Diltiazem Dosing for Atrial Fibrillation
For acute rate control in atrial fibrillation with rapid ventricular response, administer diltiazem 0.25 mg/kg IV (based on actual body weight) over 2 minutes, followed by a second bolus of 0.35 mg/kg IV over 2 minutes after 15 minutes if needed, then maintain with a continuous infusion starting at 10 mg/hour (range 5-15 mg/hour). 1, 2, 3
Initial Intravenous Bolus Dosing
First bolus: Administer 0.25 mg/kg actual body weight IV over 2 minutes (approximately 20 mg for an average 70-80 kg patient). 4, 1, 3
Second bolus (if inadequate response): After 15 minutes, give 0.35 mg/kg actual body weight IV over 2 minutes (approximately 25 mg for average patient) if heart rate reduction is insufficient. 1, 2, 3
Onset of action: Expect heart rate reduction within 2-7 minutes after IV administration, with maximal effect at approximately 4.3 minutes. 2, 5
Response definition: Adequate response is heart rate <100 bpm, ≥20% reduction from baseline, or conversion to sinus rhythm. 6, 7
Lower Dose Consideration
- Alternative low-dose approach: Doses ≤0.2 mg/kg may be equally effective (70.5% response rate) while significantly reducing hypotension risk compared to standard dosing (18% vs 35% hypotension rate, adjusted OR 0.39). 8
Continuous Intravenous Infusion
Initial infusion rate: Start at 10 mg/hour immediately following the bolus dose once heart rate control is achieved. 1, 3, 6
Titration: Increase in 5 mg/hour increments up to a maximum of 15 mg/hour if additional rate control is needed. 4, 2, 3
Alternative starting rate: Some patients may maintain adequate control with 5 mg/hour, though this is less commonly effective (47% maintained response at 10 hours vs 76% at 15 mg/hour). 3, 6
Duration limit: Do not exceed 24 hours of continuous infusion, as safety and efficacy beyond this timeframe have not been established. 3, 9
Pharmacokinetic consideration: Diltiazem exhibits dose-dependent, non-linear pharmacokinetics with decreased systemic clearance at higher infusion rates (elimination half-life 6.8-6.9 hours). 3, 9
Transition to Oral Therapy
Timing: Initiate oral diltiazem once stable rate control is maintained for at least 15-30 minutes after IV bolus or during stable continuous infusion. 2, 7
Immediate-release dosing: Start with 30-60 mg every 6 hours (120-240 mg/day total), with maximum of 90 mg every 6 hours (360 mg/day). 1, 2
Extended-release dosing: Use 180-360 mg once daily for maintenance therapy after 24-48 hours of stable control. 4, 1, 2
Discontinuation of IV infusion: Stop the continuous infusion 4 hours after administering the first oral dose. 2, 7
Transition success rate: Approximately 77% of patients maintain heart rate control during transition from IV to oral therapy. 7
Critical Contraindications
Absolute contraindications where diltiazem must NOT be used: 4, 2
- Heart failure with reduced ejection fraction (LVEF ≤40%) due to negative inotropic effects 4, 2
- Pre-excited atrial fibrillation (WPW syndrome with accessory pathway conduction) - may paradoxically accelerate ventricular response 4, 2
- Severe hypotension (systolic BP <90 mmHg) 2, 5
- Second or third-degree AV block without pacemaker 2
- Decompensated heart failure 4
Monitoring Requirements
Continuous monitoring: Assess heart rate and blood pressure continuously during bolus administration and for the first 2-4 hours after starting oral therapy. 2
Target heart rate: Aim for <100 bpm at rest or ≥20% reduction from baseline. 2, 6
Avoid excessive bradycardia: Do not allow heart rate to drop below 50 bpm. 2
Exercise assessment: In patients with activity-related symptoms, evaluate heart rate control during exercise and adjust dosing to maintain physiological range. 4, 1
Common Adverse Effects
Hypotension: Occurs in 18-42% of patients depending on dose; risk increases with standard (0.25 mg/kg) vs lower doses. 2, 8
Bradycardia and heart block: Monitor closely, especially when combining with beta-blockers. 2
Negative inotropic effects: Particularly problematic in patients with underlying systolic dysfunction. 2
Alternative Rate Control Agents
When diltiazem is contraindicated or ineffective: 4, 2
Beta-blockers (metoprolol, esmolol, propranolol) are first-line alternatives with Class I recommendation. 4, 2
Digoxin for patients with heart failure: Loading dose 0.25-0.5 mg IV, then 0.0625-0.25 mg daily maintenance. 4, 1
Amiodarone for refractory cases or when other agents fail, particularly in heart failure patients. 4
Important Clinical Pearls
Diltiazem provides rate control only and does NOT convert atrial fibrillation to sinus rhythm (though 18% may spontaneously convert during treatment). 1, 6
The drug carries a Class I recommendation with Level of Evidence B for acute rate control, making it one of the most strongly supported agents for this indication. 4, 2
Use caution when combining with beta-blockers due to additive negative chronotropic and inotropic effects. 2
Dose adjustment may be needed in patients with hepatic or renal impairment. 1
In patients with heart failure, use digoxin or amiodarone instead of diltiazem for rate control. 4, 2