What are the recommended dosing regimens for diltiazem (Cardizem) immediate‑release and extended‑release formulations in adults, including typical starting and maintenance doses?

Cardizem (Diltiazem) Dosing

For acute rate control of supraventricular tachycardia (SVT) or atrial fibrillation with rapid ventricular response, give diltiazem 0.25 mg/kg IV bolus over 2 minutes, followed by a maintenance infusion of 5-15 mg/hour if needed. 1, 2

Intravenous (IV) Dosing for Acute Settings

Initial Bolus Dose

• Standard dose: 0.25 mg/kg (typically 15-20 mg for average adult) IV over 2 minutes 1, 2, 3
• If inadequate response after 15 minutes, give second bolus of 0.35 mg/kg (20-25 mg) IV over 2 minutes 2

Maintenance Infusion

• Start at 5-10 mg/hour IV 1
• Titrate up to maximum 15 mg/hour based on heart rate response 1, 2, 3

Clinical Context

This IV dosing applies to:

• Stable narrow-complex regular tachycardias (PSVT/SVT)
• Atrial fibrillation or flutter for rate control
• Patients without accessory pathways (e.g., WPW syndrome)

Important caveat: Recent research suggests lower doses (≤0.2 mg/kg) may be equally effective with significantly lower hypotension risk 4. However, guidelines still recommend the 0.25 mg/kg standard dose, and this should be your default unless the patient has borderline blood pressure or other risk factors for hypotension.

Oral Dosing for Chronic Management

Extended-Release Formulations (Cardizem CD)

For hypertension:

• Starting dose: 180-240 mg once daily 1, 5
• Maintenance range: 240-360 mg once daily 1, 5
• Maximum studied dose: 480 mg once daily (though doses up to 540 mg have been studied) 5
• Allow 14 days to assess full antihypertensive effect before uptitrating 5

For angina:

• Starting dose: 120-180 mg once daily 5
• Maintenance range: 180-360 mg once daily
• Maximum dose: 480 mg once daily 5
• Titration can occur over 7-14 days 5

For obstructive hypertrophic cardiomyopathy (HCM):

• Use when beta-blockers are ineffective or not tolerated 6
• Dosing follows similar ranges as above, titrated to symptom relief
• Contraindicated in patients with severe dyspnea at rest, hypotension, or very high resting gradients (>100 mmHg) 6

Immediate-Release Formulations

For chronic rate control or hypertension:

• Starting dose: 120 mg daily in divided doses 1, 3
• Maintenance range: 120-360 mg daily in divided doses 1, 3
• Onset of action: 2-4 hours 3

Key Dosing Principles

Titration Strategy

• Start at lower end of dosing range
• Uptitrate based on clinical response (heart rate, blood pressure, symptoms)
• For hypertension, wait 14 days before increasing dose 5
• For angina, can titrate every 7-14 days 5

Dose-Related Adverse Effects

Side effects increase with higher doses, particularly 5:

• First-degree AV block
• Dizziness
• Sinus bradycardia
• Peripheral edema

Special Populations

• Elderly patients: Consider starting at lower end of dosing range; 200 mg once daily sustained-release is effective and well-tolerated 7
• Hepatic/renal dysfunction: Use caution and consider dose reduction 1

Critical Contraindications

Absolute contraindications 1:

• AV block greater than first-degree (without pacemaker)
• Sick sinus syndrome (without pacemaker)
• Decompensated systolic heart failure
• Hypotension
• Cardiogenic shock
• Pre-excited atrial fibrillation/flutter (WPW syndrome)

Relative contraindications:

• Concurrent use with other AV nodal blocking agents (additive effects)
• Severe LV dysfunction
• Hepatic or renal impairment

Drug Interactions

Diltiazem is a CYP3A4 substrate and moderate inhibitor 1:

• Avoid concurrent strong CYP3A4 inhibitors/inducers
• Monitor closely with: simvastatin, cyclosporine, digoxin, beta-blockers
• Contraindicated with dofetilide 1

Practical Pitfalls to Avoid

1. Hypotension risk: If concerned about hypotension, consider slower infusion (2.5 mg/min for diltiazem over up to 20 minutes) rather than 2-minute bolus 1

2. Sequential AV nodal blockers: Do NOT give diltiazem shortly after verapamil or beta-blockers due to risk of profound bradycardia 2

3. Wide-complex tachycardia: Never give diltiazem for wide-complex tachycardia of uncertain etiology—could be ventricular tachycardia 2

4. Accessory pathway: In pre-excited AF/flutter, diltiazem can paradoxically accelerate ventricular response and precipitate hemodynamic collapse 1, 2

5. Weight-based dosing matters: For IV use, calculate actual mg/kg dose rather than using arbitrary "standard" doses to optimize efficacy while minimizing hypotension 8, 4