What is the recommended dose of verapamil (calcium channel blocker) for supraventricular tachycardia (SVT)?

Verapamil Dosing for Supraventricular Tachycardia

For adult patients with SVT, administer verapamil 2.5-5 mg IV bolus over 2 minutes (over 3 minutes in older patients), with repeated doses of 5-10 mg every 15-30 minutes to a maximum total dose of 20 mg if initial response is inadequate. 1

Adult Dosing Protocol

Initial Dose:

• 2.5-5 mg IV bolus over 2 minutes
• Extend to 3 minutes in older patients
• Administer under continuous ECG and blood pressure monitoring 1, 2

Repeat Dosing (if inadequate response):

• 5-10 mg every 15-30 minutes
• Maximum total dose: 20 mg 1
• Alternative regimen: 5 mg bolus every 15 minutes to a total dose of 30 mg 1

Pediatric Dosing Protocol

Age 0-1 year:

• 0.1-0.2 mg/kg IV bolus over at least 2 minutes (usual range: 0.75-2 mg)
• Repeat same dose after 30 minutes if needed 2

Age 1-15 years:

• 0.1-0.3 mg/kg IV bolus over at least 2 minutes (usual range: 2-5 mg)
• Do not exceed 5 mg as initial dose
• Repeat dose after 30 minutes if needed (maximum single dose: 10 mg) 2
• Note: In older children (not infants), the dose is 0.1-0.3 mg/kg 1

Treatment Algorithm for SVT

1. First-line treatment: Vagal maneuvers (success rate ~28%) 3
2. Second-line treatment: Adenosine 6 mg rapid IV push followed by 20 mL saline flush (success rate 91-95%) 3
3. Third-line treatment: Verapamil or other calcium channel blockers/beta-blockers if adenosine fails 1, 3
4. Fourth-line treatment: Synchronized cardioversion for hemodynamically unstable patients or when medications fail 3

Important Precautions

Contraindications:

• Do not use in patients with:
  • Wide-complex tachycardias 1
  • Impaired ventricular function 1
  • Heart failure 1
  • Pre-excited atrial fibrillation or flutter 1
  • Wolff-Parkinson-White syndrome (use with caution - lower efficacy) 4, 5

Monitoring:

• Continuous ECG monitoring required
• Blood pressure monitoring required
• Be prepared for potential hypotension 1, 6

Drug Interactions:

• Avoid combining with other AV nodal blocking agents with longer half-lives (can cause profound bradycardia) 1
• Calcium pretreatment (1g IV) may help prevent hypotension when using verapamil infusion 7

Clinical Efficacy and Considerations

Verapamil is effective in terminating SVT in approximately 76% of episodes 4. However, it is less effective than adenosine and has a higher risk of adverse effects 1. The medication works by slowing conduction and prolonging refractoriness in the AV node 5.

For long-term management after successful conversion, oral verapamil SR (240 mg once daily) may be considered for prophylaxis, with studies showing good correlation between response to IV and oral formulations 8.

Remember that verapamil should only be used for narrow-complex SVT or arrhythmias known with certainty to be supraventricular in origin, as severe adverse effects including hypotension and cardiovascular collapse can occur if administered for ventricular tachycardia 6.