What is the recommended diltiazem dosing (IV and oral) for an adult with atrioventricular nodal re‑entrant tachycardia who has no contraindications such as severe left‑ventricular dysfunction, high‑grade atrioventricular block, or profound hypotension?

Diltiazem Dosing for AVNRT

For acute treatment of hemodynamically stable AVNRT, administer intravenous diltiazem 0.25 mg/kg as a bolus over 2 minutes, which can be followed by a continuous infusion of 5–15 mg/hour if needed; for ongoing management in patients who decline or are not candidates for catheter ablation, prescribe oral diltiazem 120–360 mg daily using extended-release formulations. 1, 2

Acute IV Management

First-Line Pharmacologic Approach

• After vagal maneuvers fail, intravenous diltiazem is a reasonable and highly effective option for acute termination of AVNRT in hemodynamically stable patients, with conversion rates of 64–98%. 1, 2

• Standard IV bolus dose: 0.25 mg/kg administered over 2 minutes. 2, 3, 4, 5

• Dose-response data: Studies demonstrate that 0.15 mg/kg, 0.25 mg/kg, and 0.45 mg/kg all achieve conversion rates >80%, significantly superior to placebo (25%). 5

• Lower-dose alternative: Doses ≤0.2 mg/kg may be equally effective (70.5% conversion rate) while significantly reducing hypotension risk compared to standard dosing (18% vs. 34.9% hypotension rate, adjusted OR 0.39). 6

• Time to conversion: Diltiazem typically terminates AVNRT within 1–3 minutes after administration. 3, 5

Continuous Infusion

• If bolus alone is insufficient, initiate a maintenance infusion at 5–10 mg/hour, which can be titrated up to 15 mg/hour as needed. 2

Comparative Efficacy

• Diltiazem vs. adenosine: Both achieve conversion rates >90%, but diltiazem avoids the transient adverse effects (flushing, chest discomfort, dyspnea) that occur frequently with adenosine. 7

• Diltiazem vs. beta-blockers: In head-to-head comparison, diltiazem was more effective than esmolol for terminating SVT. 1

Oral Therapy for Ongoing Management

Dosing Strategy

• Initial dose: Start with 120 mg once daily using extended-release formulations. 2, 8

• Titration range: Adjust dose progressively over several weeks to 120–360 mg once daily based on symptom control and tolerability. 1, 8

• Alternative formulation: Immediate-release tablets (30–90 mg) can be given in divided doses 2–3 times daily, though extended-release is preferred for adherence. 2, 8

Role in Treatment Algorithm

• Catheter ablation remains first-line definitive therapy for symptomatic AVNRT, with slow-pathway modification being potentially curative. 1

• Oral diltiazem is recommended (Class I, Level B-R) for ongoing management in patients who are not candidates for or prefer not to undergo catheter ablation. 1

Critical Contraindications and Precautions

Absolute Contraindications

• Second- or third-degree AV block without a functioning pacemaker. 1, 2, 8

• Sick sinus syndrome without a pacemaker. 2, 8

• Decompensated systolic heart failure or severe left ventricular dysfunction, as diltiazem has negative inotropic effects. 1, 2

• Wolff-Parkinson-White syndrome with atrial fibrillation/flutter, because diltiazem can accelerate ventricular response via the accessory pathway and precipitate ventricular fibrillation. 1, 2

• Cardiogenic shock or profound hypotension (systolic BP <90 mmHg). 2, 8

Critical Pitfall: Wide-Complex Tachycardia

• Never administer diltiazem for wide-complex tachycardia unless you are certain the rhythm is supraventricular in origin, as giving it for ventricular tachycardia can cause hemodynamic collapse. 1, 2

High-Risk Drug Combination

• Avoid concurrent beta-blocker therapy whenever possible, as the combination markedly increases risk of severe bradyarrhythmias, profound AV block, and heart failure exacerbation. 1, 2, 8

• If both agents are necessary, use extreme caution with close monitoring of heart rate and PR interval. 2, 8

Monitoring and Adverse Effects

Common Adverse Effects

• Hypotension is the most frequent complication, occurring in 18–42% of patients depending on dose, though symptomatic hypotension requiring intervention is less common. 6, 5

• Bradycardia and peripheral edema are dose-related effects. 2, 8

Monitoring Parameters

• Before each dose: Assess blood pressure, heart rate, and symptoms of dizziness or lightheadedness. 2

• During IV administration: Continuous cardiac monitoring is essential to detect bradyarrhythmias or AV block. 2

• After initiating oral therapy: Reassess in 1 month for symptom control, blood pressure, heart rate, and signs of heart failure. 8

Drug Interactions

• Diltiazem is both a CYP3A4 substrate and moderate CYP3A4 inhibitor, requiring caution with numerous medications. 2, 8

• Direct oral anticoagulants (apixaban, rivaroxaban): Diltiazem increases plasma concentrations and bleeding risk; monitor closely. 2, 8

• Simvastatin: Limit simvastatin dose to ≤10 mg daily when combined with diltiazem due to increased myopathy risk. 8

• Cyclosporine, tacrolimus: Diltiazem significantly increases immunosuppressant levels; dose reduction and therapeutic drug monitoring are required. 8