Adenosine

Adenosine is a naturally occurring purine nucleoside with a pivotal role in cellular energy transfer and signal transduction. Clinically, it is widely utilized as an antiarrhythmic agent for the acute termination of paroxysmal supraventricular tachycardia (PSVT) and as a diagnostic tool in cardiology.

Uses

• Supraventricular Tachycardia (SVT): Termination of paroxysmal SVT, including atrioventricular nodal reentrant tachycardia (AVNRT) and Wolff-Parkinson-White (WPW) syndrome.
• Diagnostic Aid: Assists in revealing atrial activity (e.g., flutter, fibrillation) and differentiating SVT from ventricular arrhythmias.
• Wide-Complex Tachycardia: Used as a diagnostic tool to differentiate ventricular tachycardia (VT) from SVT with aberrancy.
• Stress Testing: Pharmacologic stress agent for myocardial perfusion imaging.

Dosage and Administration

Adults:

• SVT:
  • Initial: 6 mg rapid IV bolus followed by a 20 mL saline flush.
  • If unresponsive, a second dose of 12 mg can be administered after 1-2 minutes.
  • If needed, a third 12 mg dose may be given.
• Cardiac Stress Testing:
  • Infusion: 140 mcg/kg/min IV over 4 to 6 minutes.

Pediatrics:

• SVT:
  • Initial dose: 0.1 mg/kg IV bolus (maximum 6 mg), followed by a saline flush.
  • Second dose: 0.2 mg/kg IV (maximum 12 mg) if necessary.
  • Maximum dose: 12 mg.

Administration Notes:

• Administer via a large-bore IV in a proximal vein (e.g., antecubital fossa).
• Always follow with a rapid saline flush.
• Continuous ECG monitoring during and after administration is essential.

Dose Adjustment in Different Conditions

• Renal Impairment: No dose adjustment required.
• Hepatic Impairment: No dose adjustment required.
• Heart Transplant Recipients: Lower doses may be needed due to heightened sensitivity.

Presentation and Form

• IV Solution: 3 mg/mL in 2 mL and 4 mL vials.

Pharmacokinetics

• Absorption: Administered intravenously, achieving immediate effects.
• Onset: 10 to 20 seconds.
• Duration: Less than 1 minute.
• Metabolism: Rapidly metabolized by adenosine deaminase in erythrocytes and vascular endothelial cells.
• Excretion: Metabolites are excreted in the urine.

Pharmacodynamics

• Adenosine binds to A1 receptors in the AV node, causing transient AV block and interruption of reentrant circuits.
• Additionally, it activates A2 receptors, leading to coronary vasodilation.

Drug Interactions

• Dipyridamole: Potentiates adenosine—consider dose reduction.
• Theophylline and Caffeine: Antagonize adenosine—may require higher doses.
• Carbamazepine: Increases risk of heart block.
• Beta-Blockers and Calcium Channel Blockers: May exacerbate bradycardia.

Comparison with Other Drugs in the Same Category

• Adenosine vs. Verapamil: Adenosine has a faster onset and shorter duration, making it preferable for acute termination of SVT.
• Adenosine vs. Amiodarone: Adenosine is more effective for AVNRT but less useful for atrial tachycardias.
• Adenosine vs. Digoxin: Digoxin has a slower onset and is used for chronic rate control rather than acute arrhythmia termination.

Precautions and Special Considerations

• Contraindications:
  • Second- or third-degree AV block (without pacemaker)
  • Sick sinus syndrome (without pacemaker)
  • Asthma or severe COPD (risk of bronchospasm)
  • Hypersensitivity to adenosine
• Special Populations:
  • Pediatrics: Saline flush critical for effectiveness.
  • Transplanted Hearts: Lower doses may be necessary.
• Monitoring: Continuous ECG monitoring is essential during administration.
• Administration: Use a proximal IV site for rapid delivery.
• Stress Testing: Administered as a continuous infusion rather than a bolus.

Side Effects

Common:

• Flushing
• Chest pain
• Shortness of breath (SOB)
• Dizziness

Serious:

• Bronchospasm (especially in patients with asthma)
• Bradycardia
• Hypotension
• Transient asystole

Rare:

• Proarrhythmic events, including atrial fibrillation (especially in WPW syndrome)

Recent Updates and Guidelines

• 2023 ACC/AHA Guidelines: Adenosine remains the first-line treatment for acute termination of PSVT.
• New Recommendations: Enhanced focus on ECG monitoring during administration to detect rare atrial fibrillation post-adenosine administration.

Key Facts to Remember

• Ultra-Short Half-Life: Less than 10 seconds.
• Selective AV Nodal Effect: Effective for terminating AVNRT and AVRT.
• Rapid Onset: Effects are seen within 10 to 20 seconds.
• ECG Monitoring: Essential during administration.
• Diagnostic Utility: Helps unmask atrial arrhythmias and differentiate tachycardias.

References

1. Adenosine - NCBI StatPearls https://www.ncbi.nlm.nih.gov/books/NBK519049/
2. NCBI - Pharmacological Stress Testing https://www.ncbi.nlm.nih.gov/books/NBK555963/
3. Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 13th edition.
4. Harrison’s Principles of Internal Medicine, 20th edition.
5. PALS: Pediatric dosing guidelines for SVT.