What is the recommended initial dose of adenosine (adenosine) for supraventricular tachycardia (SVT)?

Adenosine Dosing for SVT

The recommended initial dose of adenosine for supraventricular tachycardia is 6 mg administered as a rapid IV push over 1-2 seconds through a proximal vein, followed immediately by a 20 mL saline flush. 1, 2

Initial Dosing Protocol

• Start with 6 mg IV bolus given as rapidly as possible (over 1-2 seconds), not as a slow push, followed immediately by a 20 mL normal saline flush to propel the medication into central circulation before metabolism occurs 1, 2

• This initial 6 mg dose successfully converts 70-80% of PSVT cases involving AV nodal reentrant tachycardia (AVNRT) or AV reentrant tachycardia (AVRT) 2, 3

• If no conversion occurs within 1-2 minutes, administer 12 mg as a rapid IV bolus using the same technique 1, 2

• The 12 mg dose may be repeated once more if still no response after another 1-2 minutes, for a maximum cumulative dose of 30 mg 2, 3

Administration Technique Critical Points

• Use the most proximal IV access available (antecubital or higher) to ensure rapid delivery to central circulation before the drug is metabolized by its extremely short half-life of less than 10 seconds 1, 2, 4

• The rapid bolus followed by immediate saline flush is essential—adenosine must reach the heart quickly or it will be metabolized in the peripheral circulation and fail 1, 2, 4

• Maintain continuous ECG monitoring during administration to document conversion or assist with diagnostic evaluation 2

Modified Dosing for Special Populations

Reduce the initial dose to 3 mg in the following situations: 1, 2

• Patients taking dipyridamole (potentiates adenosine effect)
• Patients taking carbamazepine (increases heart block risk)
• Cardiac transplant recipients (denervated hearts are hypersensitive)
• Administration via central venous access (bypasses peripheral metabolism)

Higher doses may be required for patients with significant blood levels of: 1, 2

• Theophylline
• Caffeine
• Theobromine (these are adenosine receptor antagonists)

Clinical Context and Timing

• Attempt vagal maneuvers first (Valsalva or carotid massage), which terminate up to 25% of PSVT cases before resorting to adenosine 1, 2

• For hemodynamically unstable patients with regular narrow-complex tachycardia, adenosine may be attempted while preparations are made for synchronized cardioversion, but do not delay cardioversion 1, 2

• Have a defibrillator immediately available when administering adenosine, particularly when Wolff-Parkinson-White (WPW) syndrome is a consideration, as adenosine may precipitate rapid atrial fibrillation in these patients 1, 2

Evidence Supporting Higher Initial Dosing

While guidelines recommend starting at 6 mg, emerging evidence suggests potential benefits of a 12 mg initial dose:

• A 2025 prehospital study of 11,245 patients found that an initial 12 mg dose was associated with 65% increased odds of prehospital improvement and 28% reduction in hospital admission compared to 6 mg, with no difference in complications 5

• However, the guideline-recommended 6 mg initial dose remains the standard of care based on established American Heart Association recommendations, with the 12 mg dose reserved for non-responders 1, 2

Contraindications and Safety

Absolute contraindications: 2, 4

• Severe asthma or active bronchospasm (adenosine can precipitate life-threatening bronchospasm)

Use with extreme caution in: 1, 2, 4

• Pre-excited atrial fibrillation or flutter (may cause dangerously rapid ventricular rates)
• Second- or third-degree AV block
• Known WPW syndrome

Common transient side effects (lasting <60 seconds): 1, 4

• Flushing (most common)
• Dyspnea and chest discomfort
• Transient AV block

Diagnostic Utility Beyond Conversion

• Even when adenosine fails to terminate the arrhythmia, it may unmask the underlying rhythm by transiently slowing AV conduction, revealing atrial flutter waves or atrial tachycardia that guides subsequent therapy 2, 4

• This diagnostic effect helps distinguish between different SVT mechanisms when the initial rhythm is unclear 2

If Adenosine Fails

For stable patients after failed adenosine: 2, 4

• Consider longer-acting AV nodal blocking agents such as diltiazem (15-20 mg IV over 2 minutes) or metoprolol (5 mg IV over 1-2 minutes, repeated every 5 minutes up to 15 mg total) 1

For hemodynamically unstable patients: 2, 4

• Proceed immediately to synchronized cardioversion starting at 100 J for monomorphic regular wide-complex tachycardia or 50-100 J for narrow-complex tachycardia 1