What is the recommended dose and treatment protocol for adenosine in supraventricular tachycardia (SVT)?

Adenosine Dosing and Treatment Protocol for Supraventricular Tachycardia

For acute treatment of SVT, administer adenosine as an initial 6 mg rapid IV bolus, followed by up to two subsequent 12 mg doses if ineffective, with each dose given 1-2 minutes apart. 1, 2

Initial Dosing Protocol

• Start with 6 mg as a rapid intravenous bolus administered over 1-2 seconds, followed immediately by a rapid saline flush to ensure the medication reaches central circulation quickly 1, 2
• If no response within 1-2 minutes, administer 12 mg as a rapid IV bolus, which may be repeated once more if still no response after another 1-2 minutes 1, 2
• Maximum total dosing is up to 24 mg, which has been reported as safe in clinical practice, particularly in pregnant patients 1

Administration Technique

• Inject adenosine into an IV line as proximal to the heart as possible using a rapid bolus injection followed by immediate saline flush 2
• Administer over 1-2 seconds to maximize effectiveness, as adenosine has an extremely short half-life of less than 10 seconds 2, 3

Clinical Efficacy

• Adenosine terminates AVNRT in approximately 95% of patients and orthodromic AVRT in 90-95% of cases 1
• Onset of action is rapid, typically converting SVT within 30 seconds of administration 3
• Recent prehospital data suggests that starting with 12 mg may reduce re-dosing requirements and improve conversion rates compared to 6 mg, though guideline recommendations remain at 6 mg initial dose 4

Evidence Nuance

While the 2015 ACC/AHA/HRS guidelines recommend starting at 6 mg 1, a 2025 prehospital study found that initial 12 mg dosing was associated with 65% increased odds of patient improvement and 28% reduction in hospital admission without increased complications 4. However, guideline-based dosing should be followed in clinical practice until formal recommendations are updated.

Treatment Algorithm for SVT

Step 1: Ensure hemodynamic stability

• If hemodynamically unstable, proceed directly to synchronized cardioversion 1

Step 2: Attempt vagal maneuvers first

• Valsalva maneuver (bearing down against closed glottis for 10-30 seconds at 30-40 mm Hg) 1
• Carotid sinus massage (5-10 seconds after confirming absence of bruit) 1
• Ice-cold wet towel to face (diving reflex) 1

Step 3: Administer adenosine if vagal maneuvers fail

• 6 mg rapid IV bolus → wait 1-2 minutes → 12 mg if needed → wait 1-2 minutes → 12 mg if needed 1, 2

Step 4: If adenosine fails in stable patients

• Consider IV beta blockers, diltiazem, or verapamil 1
• Ensure absence of pre-excitation or VT before using calcium channel blockers 1

Step 5: Synchronized cardioversion

• For hemodynamically unstable patients or when pharmacological therapy fails 1

Common Adverse Effects

• Flushing, chest discomfort, dyspnea, and transient AV block occur in approximately 30% of patients but last less than 60 seconds 2, 3
• Atrial or ventricular premature complexes may occur immediately after conversion, occasionally inducing further SVT episodes requiring antiarrhythmic drugs 1
• Atrial fibrillation can be precipitated in 1-15% of cases 2

Critical Contraindications and Cautions

Absolute contraindications:

• Second- or third-degree AV block without functioning pacemaker 5
• Sinus node disease or symptomatic bradycardia without functioning pacemaker 5
• Known bronchoconstrictive or bronchospastic lung disease (asthma) 5
• Known hypersensitivity to adenosine 5

Use with extreme caution:

• Pre-excited atrial fibrillation: Adenosine may precipitate ventricular fibrillation; electrical cardioversion should be immediately available 1
• Severe asthma: Risk of bronchospasm 2, 5

Important Drug Interactions

• Dipyridamole enhances adenosine effect; reduce adenosine dose 2, 5
• Theophylline and caffeine reduce adenosine effect; higher doses may be required 2, 5
• Carbamazepine increases risk of heart block when combined with adenosine 2

Special Population: Pregnancy

• Adenosine is the first-line drug for acute SVT treatment in pregnant patients when vagal maneuvers fail 1
• Same dosing protocol applies: 6 mg initial dose, up to two 12 mg doses if needed 1
• Adverse effects to the fetus are not expected given adenosine's short half-life prevents it from reaching fetal circulation 1
• Maternal side effects (chest discomfort, flushing) are transient 1

Common Pitfalls to Avoid

• Slow administration: Adenosine must be given as a rapid bolus over 1-2 seconds, not as a slow push, or it will be metabolized before reaching the heart 2
• Inadequate saline flush: Always follow with immediate rapid saline flush 2
• Using in pre-excited AF: This can cause ventricular fibrillation; use synchronized cardioversion instead 1
• Administering calcium channel blockers without confirming rhythm: Ensure absence of VT or pre-excited AF before giving verapamil or diltiazem 1
• Distal IV access: Use the most proximal IV site available to minimize drug degradation before reaching central circulation 2