What is the recommended dose of diltiazem (Calcium Channel Blocker) for a 65-year-old male with intermittent Supraventricular Tachycardia (SVT)?

Diltiazem Dosing for Intermittent SVT in a 65-Year-Old Male

Acute Management

For acute episodes of SVT, administer diltiazem 0.25 mg/kg (approximately 15-20 mg for an average adult) IV over 2 minutes, followed by a second dose of 0.35 mg/kg (20-25 mg) after 15 minutes if the first dose fails to convert the rhythm. 1, 2

Initial IV Bolus Protocol

• First dose: 0.25 mg/kg IV over 2 minutes 1, 2
• Second dose (if needed): 0.35 mg/kg IV given 15 minutes after the first dose if no therapeutic response occurs 2
• Conversion typically occurs within 3 minutes in responding patients 3
• Studies demonstrate 84-100% conversion rates with the 0.25 mg/kg dose, significantly superior to placebo 3

Maintenance Infusion (if needed)

• Start continuous infusion at 5 mg/hour, titrating up to 15 mg/hour based on heart rate response 2
• This is reserved for patients requiring ongoing rate control after initial bolus 2

Critical Safety Monitoring During Acute Treatment

• Continuous ECG monitoring is mandatory throughout administration 2
• Frequent blood pressure measurements are essential, as hypotension is the most common adverse effect (occurring in 18-42% depending on dose) 1, 4
• Have defibrillator and resuscitation equipment immediately available 2
• Lower doses (≤0.2 mg/kg) may be equally effective with significantly less hypotension risk (adjusted OR 0.39 for hypotension vs standard dose), particularly important in elderly patients 4

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Chronic Prophylactic Management

For ongoing management of recurrent symptomatic SVT, initiate oral diltiazem at 120 mg daily (either divided doses or single dose with long-acting formulations), titrating to a maximum of 360 mg daily based on symptom control. 5, 6, 1

Oral Dosing Strategy

• Starting dose: 120 mg daily (can be divided or given as extended-release once daily) 6, 1
• Usual maintenance range: 120-360 mg daily 6
• Maximum dose: 360 mg daily 5, 6
• Titrate cautiously over several weeks to reach effective control 6

Evidence for Prophylaxis

• Oral diltiazem (270 mg daily in divided doses) prevents induction and sustenance of paroxysmal SVT in approximately 78% of patients (28 of 36 patients) 7
• The mechanism involves increasing anterograde AV nodal refractoriness and retrograde pathway refractoriness 7
• Long-term follow-up demonstrates sustained freedom from SVT attacks in patients who lose inducibility on diltiazem 7

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Absolute Contraindications (Do Not Use Diltiazem If Present)

Before administering diltiazem, you must exclude these high-risk conditions:

• Pre-excited atrial fibrillation/flutter (Wolff-Parkinson-White syndrome) - diltiazem may accelerate ventricular response and cause hemodynamic collapse 5, 1, 2
• Second or third-degree AV block without a functioning pacemaker 1, 2
• Sick sinus syndrome without a pacemaker 2
• Decompensated heart failure or severe LV dysfunction - due to negative inotropic effects 1, 2
• Hypotension (systolic BP <90 mmHg) or cardiogenic shock 1, 2

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Critical Precautions for This 65-Year-Old Patient

Age-Related Considerations

• Elderly patients (60-91 years) tolerate diltiazem well with good efficacy for SVT management 8
• However, adverse effects are more common at higher doses in elderly patients 9
• For chronic therapy in elderly patients, 180 mg/day may be optimal to balance efficacy with tolerability, as higher doses (270-360 mg/day) caused significantly more adverse effects (particularly constipation) without additional benefit 9

Drug Interactions

• Avoid concurrent beta-blockers - this combination causes profound bradycardia, AV block, and heart failure risk 2
• Diltiazem is both a CYP3A4 substrate and moderate inhibitor - exercise caution with apixaban, rivaroxaban, simvastatin, cyclosporine, and other CYP3A4 substrates 6
• Reduce warfarin dose by 50% and digoxin dose by 30-50% when initiating diltiazem 6

Common Adverse Effects to Monitor

• Hypotension (most common, especially with IV administration) 1
• Bradycardia 1
• Peripheral edema (dose-related, more common in women) 6
• Constipation (particularly problematic in elderly patients at higher doses) 9
• Worsening heart failure in patients with pre-existing ventricular dysfunction 1

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Clinical Decision Algorithm

For acute SVT episodes:

1. Confirm hemodynamic stability (if unstable → synchronized cardioversion, not medications) 2
2. Exclude WPW syndrome and other absolute contraindications 2
3. Administer diltiazem 0.25 mg/kg IV over 2 minutes 1, 2
4. If no conversion after 15 minutes → give 0.35 mg/kg 2
5. If conversion achieved but recurrence likely → start maintenance infusion 5-15 mg/hour 2

For chronic prophylaxis:

1. Start 120 mg daily (extended-release preferred for once-daily dosing) 6, 1
2. In this 65-year-old patient, consider maintaining at 180 mg/day rather than escalating to 360 mg/day to minimize adverse effects while maintaining efficacy 9
3. Reassess in 1 month after initiation or dose change 6
4. Monitor blood pressure, heart rate, and symptoms of heart failure 6