Drug Information: Adenosine
Adenosine is a naturally occurring nucleoside that acts as an antiarrhythmic. It is primarily used to treat paroxysmal supraventricular tachycardia (PSVT) by slowing conduction through the AV node, effectively interrupting re-entrant circuits and restoring normal sinus rhythm. Due to its extremely short half-life, Adenosine must be administered as a rapid intravenous bolus followed by a saline flush. It is also sometimes used diagnostically to unmask atrial flutter or fibrillation when these arrhythmias are concealed by rapid AV conduction.
Category
Antiarrhythmic
Mechanism of Action
Adenosine works by slowing AV nodal conduction. Specifically, it binds to A1 receptors on cardiac cells, primarily in the sinoatrial (SA) and atrioventricular (AV) nodes. This binding activates a G-protein-coupled mechanism. The G protein then activates a potassium channel (IKAdo), increasing potassium efflux from the cell. This hyperpolarizes the cell membrane, making it more difficult to depolarize and thus slowing the rate of spontaneous firing in the SA node and decreasing conduction velocity through the AV node. Adenosine also inhibits the influx of calcium, further contributing to the slowing of AV nodal conduction. By transiently blocking AV nodal conduction, Adenosine can interrupt re-entrant circuits that cause PSVT, allowing normal sinus rhythm to resume. Its effects are very short-lived due to rapid uptake by erythrocytes and endothelial cells.
Clinical Uses
The primary clinical use of Adenosine is for the acute treatment of paroxysmal supraventricular tachycardia (PSVT). PSVT is a type of arrhythmia characterized by a rapid heart rate originating above the ventricles. Adenosine is effective in terminating PSVT by interrupting the re-entrant circuit that causes the rapid heart rate. Beyond PSVT, Adenosine can also be used as a diagnostic tool to help differentiate between different types of supraventricular tachycardias. By transiently slowing AV conduction, it can unmask underlying atrial activity, such as atrial flutter or atrial fibrillation, that might be concealed by rapid AV conduction. Adenosine may also be used during cardiac stress testing as an alternative to exercise to induce coronary vasodilation, although other agents are more commonly used for this purpose.
Dosage
Adult Dosage: The typical initial dose of Adenosine is 6 mg administered as a rapid intravenous bolus over 1-2 seconds, followed immediately by a 20 mL saline flush. If the PSVT does not terminate within 1-2 minutes, a second dose of 12 mg can be given, again as a rapid IV bolus followed by a saline flush. A third dose is generally not recommended. The dose should be administered as close to the heart as possible (e.g., antecubital fossa).
Pediatric Dosage: The initial dose is 0.05-0.1 mg/kg as a rapid IV bolus followed by a saline flush. The maximum single dose is 6 mg. If the initial dose is ineffective, the dose may be doubled every 2 minutes up to a maximum dose of 0.25 mg/kg or 12 mg.
Indications
Common indications for Adenosine include:
* Paroxysmal Supraventricular Tachycardia (PSVT)
* Diagnosis of wide-complex tachycardia
* Pharmacologic stress testing
Contraindications
Contraindications for Adenosine use include:
* Second- or third-degree AV block (without a pacemaker)
* Sick sinus syndrome (without a pacemaker)
* Symptomatic bradycardia
* Known hypersensitivity to Adenosine
* Bronchoconstrictive or obstructive lung disease (relative contraindication)
FAQ
Q: What is Adenosine used for?
A: Adenosine is primarily used to treat paroxysmal supraventricular tachycardia (PSVT) by slowing conduction through the AV node and restoring normal sinus rhythm.
Q: How is Adenosine administered?
A: Adenosine is administered as a rapid intravenous bolus, followed immediately by a saline flush.
Q: What are the common side effects of Adenosine?
A: Common side effects include flushing, chest pain or pressure, shortness of breath, nausea, and dizziness. These effects are usually brief due to Adenosine’s short half-life.
Q: Why is Adenosine given as a rapid bolus?
A: Adenosine has a very short half-life (less than 10 seconds) in the bloodstream. Rapid bolus administration ensures that a sufficient concentration of the drug reaches the heart quickly to have the desired effect.
Q: Can Adenosine be used in patients with asthma?
A: Adenosine can cause bronchospasm, so it should be used with caution in patients with asthma or other bronchoconstrictive lung diseases. It may be a relative contraindication.
Q: What should I do if Adenosine doesn’t terminate the PSVT?
A: If the initial dose of Adenosine is ineffective, a higher dose can be administered. If the PSVT persists after a second dose, other antiarrhythmic medications or cardioversion may be necessary.
Q: Does caffeine affect Adenosine?
A: Yes, caffeine is an adenosine receptor antagonist and can reduce the effectiveness of adenosine. Patients taking theophylline (another adenosine antagonist) may also require higher doses of adenosine.
Q: What are the signs that Adenosine has worked?
A: The primary sign that Adenosine has worked is the termination of the PSVT and the return of a normal sinus rhythm on the ECG. There may be a brief period of asystole or bradycardia immediately following administration, which is usually self-limiting.
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