Half-Life of Adenosine
Adenosine has an extremely short half-life of less than 10 seconds in the circulation. 1, 2 This remarkably brief duration of action makes it uniquely valuable for both diagnostic and therapeutic cardiovascular applications.
Pharmacokinetics of Adenosine
Distribution and Metabolism
- Intravenously administered adenosine distributes from circulation via cellular uptake, primarily by:
- Erythrocytes (red blood cells)
- Vascular endothelial cells 2
- This process involves a specific transmembrane nucleoside carrier system that is:
- Reversible
- Nonconcentrative
- Bidirectionally symmetrical 2
Elimination Pathway
- Extracellular adenosine is primarily cleared from plasma by cellular uptake
- Excessive amounts may be deaminated by an ecto-form of adenosine deaminase 2
- Once inside the cell, adenosine is rapidly:
- Phosphorylated by adenosine kinase to adenosine monophosphate, or
- Deaminated by adenosine deaminase to inosine 2
Clinical Implications of Short Half-Life
Advantages
- Allows for rapid titration of dosing during treatment of supraventricular tachycardia (SVT) 3
- Adverse effects are typically transient, resolving within seconds to minutes after administration 4
- Does not require dose adjustment in renal or hepatic impairment 2
- Enables safe use in diagnostic procedures like stress testing 5
Administration Considerations
- Must be administered as a rapid IV bolus followed immediately by saline flush 4
- Should be injected into a proximal or central IV line to ensure rapid delivery to the heart 4
- Initial dose is typically 6 mg, with subsequent doses of 12 mg if needed 4
- Continuous ECG monitoring during administration is essential 4
Practical Applications
SVT Management
- The ultra-short half-life makes adenosine ideal for acute termination of SVT, with success rates of 78-96% 4
- While effective at terminating acute episodes, the short half-life means adenosine will not prevent recurrence of SVT 6
- Additional antiarrhythmic medications should be considered if prophylaxis against recurrence is required 6
Diagnostic Applications
- The transient AV nodal blockade produced by adenosine helps differentiate various tachyarrhythmias 4
- Can unmask atrial flutter or atrial tachycardia by temporarily blocking AV conduction 4
Reversal of Effects
- Due to the extremely short half-life, adverse effects typically resolve spontaneously
- In cases of persistent adverse reactions, methylxanthines such as theophylline can be used as competitive adenosine receptor antagonists 2
The remarkably short half-life of adenosine is central to its clinical utility, allowing for both effective treatment of SVT and valuable diagnostic applications while minimizing the duration of potential adverse effects.