What is the recommended dosing for adenosine (adenosine) in the treatment of supraventricular tachycardia (SVT)?

Adenosine Dosing for Supraventricular Tachycardia

For acute treatment of SVT, administer adenosine 6 mg as a rapid IV bolus over 1-2 seconds through a proximal vein, followed immediately by a 20 mL saline flush; if unsuccessful after 1-2 minutes, give 12 mg rapid IV bolus, which may be repeated once more for a maximum total dose of 30 mg. 1, 2

Initial Dosing Protocol

• Start with 6 mg IV push administered over 1-2 seconds, not 12 mg, as the initial dose successfully converts 70-80% of PSVT cases involving AVNRT or AVRT 2, 3
• Use the most proximal IV access available (antecubital or higher) to ensure rapid delivery to central circulation before the drug is metabolized 2, 4
• Follow immediately with a rapid 20 mL saline flush to propel the medication into central circulation 2, 4
• Administer as a true rapid bolus over 1-2 seconds, not a slow push—this is critical for efficacy 2

Subsequent Dosing if Initial Dose Fails

• If no conversion occurs within 1-2 minutes, administer 12 mg 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 1, 2
• Maximum total cumulative dose is 30 mg (6 mg + 12 mg + 12 mg), though some guidelines cite 24 mg as the safe maximum 1, 2, 3
• Overall conversion rates with this protocol range from 78% to 96% for AVNRT or AVRT 2, 3

Modified Dosing for Special Populations

Reduce initial dose to 3 mg in the following situations: 2, 4

• Patients taking dipyridamole (potentiates adenosine effect)
• Patients taking carbamazepine (increases risk of heart block)
• Cardiac transplant recipients (denervated hearts are hypersensitive)
• Administration via central venous access (drug reaches heart faster with less degradation) 5

Increase doses may be required for patients with significant blood levels of: 2, 4

• Theophylline
• Caffeine
• Theobromine (methylxanthines competitively antagonize adenosine receptors)

Administration Technique Critical Points

• Maintain continuous ECG monitoring during administration to document conversion or aid diagnostic evaluation 2
• Have a defibrillator immediately available, particularly when Wolff-Parkinson-White syndrome is a consideration, as adenosine can precipitate atrial fibrillation with rapid ventricular rates 4
• Position the patient supine if possible, as transient hypotension may occur 1

Expected Adverse Effects (Usually Transient, <60 seconds)

• Flushing, chest discomfort/pain, and dyspnea are the most common side effects 1, 3
• Transient AV block (expected therapeutic effect) 1
• Rare but important: bronchospasm, complete heart block, initiation of atrial fibrillation (occurs in 1-15% of cases) 3
• All adverse effects typically resolve within 60 seconds due to adenosine's half-life of less than 10 seconds 1, 6

Absolute Contraindications

• Second- or third-degree AV block without a functioning pacemaker 1, 7
• Sinus node disease (sick sinus syndrome, symptomatic bradycardia) without a functioning pacemaker 1, 7
• Severe asthma or active bronchospasm (adenosine can precipitate life-threatening bronchospasm) 2, 3, 4, 7
• Known hypersensitivity to adenosine 7

Use With Extreme Caution

• Pre-excited atrial fibrillation or flutter (can cause accelerated ventricular response) 1, 3
• Wolff-Parkinson-White syndrome with atrial fibrillation 4

Pregnancy Considerations

• Adenosine is safe and effective during pregnancy 1, 4
• Use the standard dosing protocol: 6 mg initial dose, followed by up to two 12 mg doses if needed 1
• Adverse effects to the fetus are not expected given adenosine's extremely short half-life prevents it from reaching fetal circulation 1
• Maternal side effects (chest discomfort, flushing) are transient 1

If Adenosine Fails

• For hemodynamically stable patients, consider longer-acting AV nodal blocking agents such as IV diltiazem or metoprolol 2, 3, 4
• For hemodynamically unstable patients, proceed immediately to synchronized cardioversion 2, 3
• Adenosine may unmask atrial flutter or atrial tachycardia by transiently slowing AV conduction, even when it doesn't terminate the arrhythmia—this diagnostic information guides subsequent therapy 2, 3

Common Pitfalls to Avoid

• Do not use slow IV push—adenosine must be given as a rapid 1-2 second bolus or it will be metabolized before reaching the heart 2
• Do not forget the saline flush—without immediate flush, the drug may not reach central circulation in time 2, 4
• Do not use distal IV sites—peripheral hand or wrist IVs significantly reduce efficacy 2, 4
• Do not start with 12 mg—the 6 mg dose converts 70-80% of cases with fewer side effects 2, 3
• Do not give to asthmatics—this is an absolute contraindication due to risk of severe bronchospasm 4, 7