What is an appropriate starting dose of diltiazem for an adult with supraventricular tachycardia?

Intravenous Diltiazem Dosing for Acute SVT

For acute supraventricular tachycardia in hemodynamically stable adults, administer intravenous diltiazem 0.25 mg/kg (approximately 15-20 mg for an average adult) over 2 minutes, followed by a second dose of 0.35 mg/kg (20-25 mg) after 15 minutes if the initial dose fails to terminate the arrhythmia or adequately control the ventricular rate. 1, 2

Treatment Algorithm

First-Line Therapy

• Attempt vagal maneuvers (Valsalva, carotid sinus massage, or ice-cold towel to face) before any pharmacologic intervention 3
• Adenosine remains the preferred first-line medication due to its rapid action and short half-life, with approximately 95% efficacy in terminating AVNRT 3

Second-Line: Diltiazem Administration

• Initial bolus: 0.25 mg/kg IV over 2 minutes 1, 2, 4, 5
• Second bolus (if needed): 0.35 mg/kg IV administered 15 minutes after the first dose if tachycardia persists 2
• Continuous infusion: Start at 5 mg/hour and titrate up to 15 mg/hour based on heart rate response for ongoing rate control 2
• Median time to conversion is 2 minutes after completing the infusion 5

Efficacy Data

• The 0.25 mg/kg dose achieves 100% conversion in AV nodal reentrant tachycardia and 81-86% conversion in AV reciprocating tachycardia 4, 5
• Lower doses (0.15 mg/kg) show 84% efficacy, while doses below 0.15 mg/kg drop to only 29% efficacy 4

Critical Contraindications (Must Exclude Before Administration)

Absolute contraindications:

• Pre-excited atrial fibrillation or flutter (Wolff-Parkinson-White syndrome with anterograde accessory pathway conduction)—diltiazem can accelerate ventricular response and precipitate ventricular fibrillation 1, 2
• Second- or third-degree AV block without a functioning pacemaker 1, 2
• Decompensated heart failure or severe left ventricular dysfunction 1, 2
• Hypotension (systolic BP <90 mmHg) 1, 2
• Sick sinus syndrome without a pacemaker 2
• Cardiogenic shock 2

Critical pre-administration step:

• Rule out ventricular tachycardia and pre-excited atrial fibrillation/flutter on ECG before giving diltiazem—administering diltiazem for these rhythms can cause hemodynamic collapse 3, 2

Monitoring Requirements

• Continuous ECG monitoring throughout administration 2
• Frequent blood pressure measurements (every 2-5 minutes during bolus and initial infusion) 2
• Defibrillator and resuscitation equipment must be immediately available 1, 2

Common Adverse Effects and Management

• Hypotension is the most common adverse effect, occurring in 18-42% of patients depending on dose 3, 1, 6
  • Lower doses (≤0.2 mg/kg) reduce hypotension risk by 61% compared to standard dosing (adjusted OR 0.39) while maintaining equivalent efficacy 6
  • Symptomatic hypotension occurs in only 6-8% of patients 4, 5
• Bradycardia may occur, particularly in patients with underlying conduction disease 3, 1
  • Treat severe bradycardia with atropine or temporary pacing 1

Important Clinical Pitfalls

• Never combine diltiazem with beta-blockers acutely—this combination causes profound bradycardia, high-degree AV block, and worsening heart failure 2
• Do not use diltiazem for wide-complex tachycardias unless the rhythm is known with certainty to be supraventricular in origin 2
• Diltiazem works by slowing AV nodal conduction and has no effect on accessory pathway conduction 5
• In hemodynamically unstable patients, skip medications entirely and proceed directly to synchronized cardioversion 3, 2

Oral Maintenance Dosing (After Acute Conversion)

• Starting dose: 120 mg daily in divided doses or as a single dose with long-acting formulations 3
• Maintenance range: 120-360 mg daily 3
• Maximum daily dose is 360 mg to minimize long-term adverse effects 3