What is the recommended acute adenosine dosing for a hemodynamically stable patient with supraventricular tachycardia, including weight‑based adjustments and contraindications?

Adenosine Dosing for Acute Supraventricular Tachycardia

For hemodynamically stable patients with SVT, administer adenosine 6 mg as a rapid IV push over 1–2 seconds through a proximal vein, followed immediately by a 20 mL saline flush; if no conversion occurs within 1–2 minutes, give 12 mg IV push, and repeat 12 mg once more if needed (maximum cumulative dose 30 mg). 1, 2, 3

Standard Dosing Protocol

• First dose: 6 mg rapid IV bolus administered over 1–2 seconds, followed immediately by 20 mL saline flush 1, 2, 3
• Second dose: 12 mg rapid IV bolus if no conversion within 1–2 minutes 1, 2, 3
• Third dose: 12 mg rapid IV bolus may be repeated once more if still no response 1, 2, 3
• Maximum cumulative dose: 30 mg total (6 mg + 12 mg + 12 mg) 2, 3

The 6 mg initial dose successfully converts 70–80% of PSVT cases involving AVNRT or AVRT, with overall conversion rates of 90–95% for AVNRT and 78–96% for AVRT across all doses. 2, 3

Critical Administration Technique

• Use the most proximal IV access available (antecubital preferred over distal sites) to ensure rapid delivery to central circulation before the drug is metabolized 2, 3
• Administer as a rapid bolus over 1–2 seconds, not a slow push—adenosine's half-life is less than 10 seconds, requiring immediate delivery 1, 2, 3
• Follow immediately with 20 mL saline flush to propel the medication into central circulation 1, 2, 3
• Maintain continuous ECG monitoring during administration to document conversion or aid diagnostic evaluation 2, 3

Weight-Based Adjustments and Special Populations

Reduced Initial Dose (3 mg)

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

• Patients taking dipyridamole (potentiates adenosine effect) 1, 2
• Patients taking carbamazepine (potentiates adenosine effect) 2, 3
• Cardiac transplant recipients (denervated hearts are hypersensitive) 2, 3
• Administration via central venous access (bypasses peripheral degradation) 2, 3

Increased Dose Requirements

Larger doses may be required for patients with significant blood levels of: 1, 2, 3

• Theophylline (competitive antagonist at adenosine receptors) 1, 2, 3
• Caffeine (competitive antagonist) 1, 2, 3
• Theobromine (competitive antagonist) 2, 3

Single bolus doses of 18 mg have been reported as safe in clinical practice, particularly in patients with impaired venous return or those taking methylxanthines. 2, 4

Absolute Contraindications

• Asthma or active bronchospasm—adenosine can precipitate severe bronchospasm and is absolutely contraindicated 1, 2, 3
• Second- or third-degree AV block or sick sinus syndrome without a pacemaker 1, 2
• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome)—adenosine may initiate atrial fibrillation with rapid ventricular rates, potentially triggering ventricular fibrillation 1, 2

A defibrillator must be readily available when administering adenosine, particularly in patients where WPW syndrome is a consideration. 2, 3

Expected Response and Timing

• Average time to termination: approximately 30 seconds after an effective dose 2
• If no effect within 1–2 minutes, the dose is considered insufficient and the next higher dose should be administered 1, 2, 3
• Early recurrence of tachycardia occurs in up to one-third of patients due to adenosine's ultra-short half-life 5

Common Side Effects

Most side effects are transient and self-limited (lasting less than 60 seconds) due to adenosine's very short half-life: 1, 2

• Flushing (most common) 1, 2
• Dyspnea 1, 2
• Chest discomfort or pain 1, 2
• Transient AV block 1
• Premature ventricular contractions 1

Management After Adenosine Administration

If Conversion Occurs

• Monitor continuously for recurrence—premature complexes post-conversion commonly trigger recurrent SVT episodes 2
• If immediate recurrence occurs, consider a longer-acting AV nodal blocking agent (diltiazem or β-blocker) to prevent reinitiation 1, 2

If Adenosine Fails to Convert

• Adenosine may unmask underlying atrial flutter or atrial tachycardia by transiently slowing AV conduction, even when it doesn't terminate the arrhythmia—this diagnostic effect guides subsequent therapy 2, 3
• For stable patients: administer a longer-acting AV nodal blocker—IV diltiazem 15–20 mg over 2 minutes (64–98% conversion rate) or IV metoprolol 2.5–5 mg every 2–5 minutes (maximum 15 mg) 1, 2
• For unstable patients: proceed immediately to synchronized cardioversion 1, 2

Critical Safety Warnings

Do NOT administer verapamil or diltiazem (alternative agents) if any of the following are present: 2

• Ventricular tachycardia cannot be excluded
• Pre-excited atrial fibrillation (WPW syndrome)
• Suspected systolic heart failure
• Hemodynamic instability

Pregnancy Considerations

• Adenosine is safe and effective during pregnancy and is the preferred pharmacologic agent after vagal maneuvers 2, 3
• If the patient becomes hemodynamically unstable, electrical cardioversion is indicated 2