What are the considerations for administering adenosine (adenosine) in patients with supraventricular tachycardia (SVT)?

Adenosine Administration Considerations for SVT

Adenosine should be administered as a 6 mg rapid IV push through a large proximal vein followed immediately by a 20 mL saline flush, with subsequent 12 mg doses at 1-2 minute intervals if needed, while having a defibrillator and resuscitative equipment immediately available. 1, 2

Administration Protocol

Standard Dosing

• Initial dose: 6 mg IV push through a large proximal vein, followed immediately by 20 mL saline flush 1
• If no conversion within 1-2 minutes, administer 12 mg IV push 1
• May repeat 12 mg dose once more if needed 1
• The rapid bolus followed by immediate saline flush is critical due to adenosine's extremely short half-life of less than 10 seconds 2

Modified Dosing Situations

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if administered via central venous access 1
• Increase doses may be required in patients with significant blood levels of theophylline, caffeine, or theobromine, as these methylxanthines interfere with adenosine activity 1, 3
• Patients with impaired venous return (e.g., right heart failure, pulmonary hypertension) may require higher-than-standard doses due to delayed drug delivery to the heart 4

Critical Safety Requirements

Equipment and Monitoring

• A defibrillator must be available when administering adenosine, particularly in patients where Wolff-Parkinson-White syndrome is a consideration, due to risk of initiating atrial fibrillation with rapid ventricular rates 1
• Continuous ECG recording during administration helps distinguish between drug failure and successful termination with immediate reinitiation 1
• Monitor blood pressure, ECG, respiratory status, and capillary refill before, during, and after administration 5

Resuscitative Preparedness

• Appropriate resuscitative measures and personnel must be immediately available, as fatal and nonfatal cardiac arrest, sustained ventricular tachycardia, and myocardial infarction have occurred following adenosine administration 3

Absolute Contraindications

Do not administer adenosine in patients with: 3

• Second- or third-degree AV block (unless functioning pacemaker present)
• Sinus node dysfunction or sick sinus syndrome (unless functioning pacemaker present)
• Asthma or bronchospastic/bronchoconstrictive lung disease - adenosine can cause severe bronchospasm 1, 3
• Known hypersensitivity to adenosine
• Acute myocardial ischemia, unstable angina, or cardiovascular instability 3

Relative Contraindications and Cautions

Use with Extreme Caution In:

• Pre-existing first-degree AV block or bundle branch block 3
• Obstructive lung disease without bronchoconstriction (e.g., emphysema, bronchitis) 3
• Autonomic dysfunction, hypovolemia, stenotic valvular heart disease, pericarditis, or stenotic carotid artery disease 3

Common Pitfall to Avoid:

Never give adenosine to asthmatics - this is the most critical contraindication in emergency practice, as bronchospasm can be severe and life-threatening 1, 3

Expected Side Effects

Transient Effects (Usually <60 seconds)

• Flushing, dyspnea, and chest discomfort are the most common side effects 1, 2
• Transient AV block occurs in approximately 6% of patients (first-degree 3%, second-degree 3%, third-degree 0.8%) 3
• Other effects include headache, throat/neck/jaw discomfort, gastrointestinal discomfort, dizziness 3
• These effects are dose-dependent but typically resolve within 60 seconds due to the ultra-short half-life 2

Serious Adverse Events Requiring Discontinuation:

• Persistent or symptomatic high-grade AV block 3
• Severe respiratory difficulties 3
• Persistent or symptomatic hypotension 3
• New-onset or recurrent seizures (do not use methylxanthines like aminophylline for reversal, as this increases seizure risk) 3

Diagnostic and Therapeutic Value

Dual Purpose

• Adenosine serves both therapeutic and diagnostic functions, with 78-96% success rate in terminating AVNRT and AVRT 1
• Can unmask underlying atrial flutter or atrial tachycardia by causing transient AV block, revealing flutter waves 1, 2
• If adenosine reveals another form of SVT (e.g., atrial flutter), consider longer-acting AV nodal blocking agents like diltiazem or beta-blockers 1

Post-Conversion Management

• Monitor for recurrence after successful conversion 1
• Treat recurrence with repeat adenosine or consider longer-acting AV nodal blocking agents 1
• Adenosine does not prevent reinitiation of SVT due to its ultra-short half-life, so prophylactic therapy should be considered if recurrence occurs 5

Special Populations

Pregnancy

• Adenosine is safe and effective during pregnancy 1

Pediatric Considerations

• Pediatric dosing differs: initial dose 0.05-0.1 mg/kg IV bolus, increased in 0.05 mg/kg increments every 1-2 minutes to maximum 0.25 mg/kg 5, 6
• Efficacy and safety profile similar to adults, with transient side effects 6

Drug Interactions

Potentiating Interactions

• Dipyridamole significantly enhances adenosine effects - reduce initial dose to 3 mg 1, 2
• Carbamazepine also potentiates effects - reduce initial dose to 3 mg 1

Antagonizing Interactions

• Methylxanthines (theophylline, caffeine, theobromine) reduce adenosine effectiveness - larger doses may be required 1, 3
• Patients should ideally avoid caffeine intake before adenosine administration when possible 1