What is the recommended starting dose and titration schedule for a diltiazem (calcium channel blocker) drip?

Diltiazem Drip Dosing for Rate Control

The recommended starting dose for a diltiazem drip is 0.25 mg/kg IV bolus over 2 minutes (approximately 20 mg for an average patient), followed by an initial infusion rate of 5-10 mg/hour, which can be titrated up to 15 mg/hour as needed. 1

Initial Bolus Administration

• Initial bolus dose: 0.25 mg/kg IV over 2 minutes (approximately 20 mg for average adult) 1, 2
• If response is inadequate after 15 minutes, a second bolus of 0.35 mg/kg IV over 2 minutes (approximately 25 mg for average adult) can be administered 1
• Some patients may respond to a lower initial dose of 0.15 mg/kg, though duration of action may be shorter 1
• Recent evidence suggests that lower doses (≤0.2 mg/kg) may be as effective as standard doses while reducing the risk of hypotension 3

Continuous Infusion

• Initial infusion rate: 10 mg/hour (5 mg/hour may be appropriate for some patients) 1
• Titration: Increase in 5 mg/hour increments up to maximum of 15 mg/hour as needed 1
• Duration: Infusion may be maintained for up to 24 hours; longer durations have not been studied 1

Dilution Guidelines

For continuous infusion, diltiazem can be prepared as follows:

• 125 mg (25 mL) in 100 mL diluent = 1 mg/mL concentration
• 250 mg (50 mL) in 250 mL diluent = 0.83 mg/mL concentration
• 250 mg (50 mL) in 500 mL diluent = 0.45 mg/mL concentration 1

Compatible diluents include Normal Saline, D5W, or D5W/0.45% NaCl 1

Monitoring Parameters

• Heart rate: Target is generally 60-80 bpm at rest and 90-115 bpm during moderate exercise 2
• Blood pressure: Monitor for hypotension (a common adverse effect)
• Cardiac rhythm: Continuous monitoring for bradycardia or conduction abnormalities 4
• Signs of heart failure: Diltiazem has negative inotropic effects 2

Efficacy and Response

• Approximately 77% of patients maintain heart rate control when transitioning from IV to oral diltiazem 5
• Higher weight-based dosing (≥0.13 mg/kg) has been associated with faster achievement of heart rate control compared to lower doses 6

Contraindications and Cautions

• Contraindicated in:
  • Pre-excitation syndromes (e.g., WPW with atrial fibrillation/flutter)
  • Decompensated heart failure
  • Severe left ventricular dysfunction 4
• Use with caution in patients with:
  • First-degree AV block
  • Hypotension
  • Impaired liver or kidney function 4

Adverse Effects Management

• Hypotension: Occurs in 18-42% of patients, with higher rates at higher doses 3
• Avoid fluid boluses to counteract hypotension in patients with heart failure 4
• Bradycardia and heart block: Monitor closely, especially when combined with beta-blockers 4

Transition to Oral Therapy

• For continued rate control beyond 24 hours, transition to oral diltiazem
• Oral diltiazem dosage: 120-360 mg daily in divided doses 2
• Median effective dose of extended-release formulation: 300 mg/day 5
• Administer oral dose 4 hours before discontinuing IV infusion to ensure smooth transition 5

Clinical Pearls

• Diltiazem shows dose-dependent, non-linear pharmacokinetics 1
• Lower doses (≤0.2 mg/kg) may provide adequate rate control with lower risk of hypotension 3
• Keep diluted diltiazem refrigerated and use within 24 hours 1
• For patients with heart failure or LV dysfunction, consider alternative agents like digoxin or amiodarone 2

By following this evidence-based approach to diltiazem drip administration, clinicians can effectively manage rapid ventricular rates while minimizing adverse effects.