What is the recommended adenosine dose and administration protocol for an adult with regular narrow‑complex paroxysmal supraventricular tachycardia and no contraindications such as high‑grade atrioventricular block, sick sinus syndrome without a pacemaker, severe asthma, or adenosine hypersensitivity?

Adenosine Dosing for Paroxysmal Supraventricular Tachycardia

The recommended adenosine dose for acute termination of PSVT in adults is 6 mg rapid IV push followed immediately by a 20 mL saline flush, with subsequent 12 mg doses if conversion does not occur within 1–2 minutes, up to a maximum cumulative dose of 30 mg (6 mg + 12 mg + 12 mg). 1

Standard Dosing Protocol

• First dose: Administer 6 mg as a rapid IV bolus over 1–2 seconds through a large proximal vein (antecubital preferred), followed immediately by a 20 mL saline flush. 1

• Second dose: If no conversion within 1–2 minutes, give 12 mg rapid IV push with saline flush. 1

• Third dose: If still no response, administer a final 12 mg rapid IV bolus. 1

• Maximum cumulative dose: 30 mg total (6 mg + 12 mg + 12 mg). 1

Why This Stepwise Approach?

• The 6 mg initial dose converts 70–80% of PSVT episodes, making it effective for most patients while minimizing dose-dependent side effects. 1

• Overall conversion rates across all dosing steps are 90–95% for AVNRT and 78–96% for AVRT. 1, 2

• Adenosine has an extremely short half-life of <10 seconds, so ineffective doses are rapidly cleared, allowing safe escalation within 1–2 minutes. 1, 3

• The average time to termination after an effective dose is approximately 30 seconds; if no effect occurs within 1–2 minutes, the dose is insufficient. 1

Critical Administration Technique

• Use the most proximal IV access available (antecubital vein strongly preferred over distal hand veins) because adenosine degrades rapidly before reaching the heart. 1

• Deliver as a rapid push over 1–2 seconds—a slower injection is ineffective due to the drug's ultrashort half-life. 1

• Follow immediately with a 20 mL saline flush to propel the medication into the central circulation. 1

Dose Adjustments for Special Populations

Reduce Initial Dose to 3 mg in:

• Patients taking dipyridamole (potentiates adenosine effect). 1

• Patients taking carbamazepine (potentiates adenosine effect). 1

• Cardiac transplant recipients (denervated hearts are hypersensitive). 1

• Administration via central venous access (bypasses peripheral degradation). 1

Increase Dose Requirements in:

• Patients with significant blood levels of theophylline, caffeine, or theobromine (competitive antagonists at adenosine receptors). 1, 4

• Patients with impaired venous return (e.g., right heart failure, pulmonary hypertension) may require doses higher than the standard 30 mg maximum—single 18 mg boluses have been reported as safe in clinical practice. 1, 5

Absolute Contraindications

• Asthma or active bronchospasm—risk of severe, life-threatening bronchospasm. 1, 2

• Second- or third-degree AV block or sick sinus syndrome without a pacemaker. 1

• Pre-excited atrial fibrillation (e.g., Wolff-Parkinson-White syndrome)—adenosine can trigger rapid ventricular response or ventricular fibrillation. 1, 6

Expected Transient Side Effects (<60 seconds)

• Flushing (most common). 1

• Dyspnea. 1, 3

• Chest discomfort or pain. 1, 3

• Transient AV block. 1

• Premature ventricular contractions. 1

These effects resolve spontaneously within 1 minute due to adenosine's ultrashort half-life and do not require treatment. 4, 3

Management After Adenosine Administration

If Conversion Occurs:

• Continue continuous ECG monitoring for early recurrence, as premature atrial or ventricular complexes commonly trigger repeat SVT episodes. 1

• If immediate recurrence occurs, administer a longer-acting AV-nodal blocker such as IV diltiazem 15–20 mg over 2 minutes or a β-blocker. 1, 2

If Adenosine Fails to Convert:

• In hemodynamically stable patients, proceed to 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

• In hemodynamically unstable patients (hypotension, altered mental status, shock, chest pain, acute heart failure), proceed immediately to synchronized cardioversion (50–100 J initial energy). 2, 6

Common Pitfalls to Avoid

• Never administer adenosine slowly—the drug will be completely degraded before reaching the heart. 1

• Never use distal hand IV access when proximal access is available—peripheral degradation reduces efficacy. 1

• Never give adenosine without immediately following with a saline flush—the bolus will not reach the central circulation in time. 1

• Never administer adenosine to patients with asthma—this can precipitate life-threatening bronchospasm. 1, 2

• Never give adenosine if pre-excited atrial fibrillation (WPW) cannot be excluded—obtain a 12-lead ECG during tachycardia to rule out delta waves. 1, 6

Diagnostic Value Beyond Therapy

• Adenosine serves a dual therapeutic-diagnostic role: it terminates AV-nodal dependent SVT but can unmask underlying atrial flutter or atrial tachycardia by producing transient AV block, revealing the underlying atrial rhythm. 1, 4

• In wide-complex tachycardias, adenosine helps distinguish SVT with aberrancy from ventricular tachycardia—unlike verapamil, adenosine is safe in ventricular tachycardia. 4