Adenosine (Adenocard®, Adenoscan®)

Drug Overview
Class	Antiarrhythmics
Subclass	Miscellaneous (AV Nodal Suppressant)
Primary Use	Paroxysmal SVT
Route	IV rapid bolus
Onset	Seconds
Duration	< 10 seconds
Half-life	~10 seconds
Metabolism	Rapid uptake by RBCs & vascular endothelium
Elimination	Intracellular metabolism
Pregnancy	Category C
Renal Adjustment	No
Hepatic Adjustment	No
Black Box Warning	No
Controlled	No
FDA Approval	1989

Overview

Adenosine is an ultra–short-acting endogenous nucleoside used for rapid termination of AV node–dependent supraventricular tachycardias.

It transiently blocks AV nodal conduction, interrupting reentry circuits involving the AV node.

It is diagnostic and therapeutic in narrow-complex tachycardias.

Mechanism of Action

Primary Target:

A1 adenosine receptors in the AV node

Signal Pathway:

Gi protein activation
↓ cAMP
↑ outward potassium current
Hyperpolarization of AV nodal tissue

Net Effect:

Transient AV nodal block
Slowed conduction velocity
Increased refractoriness

Why It Works:

AV node–dependent reentry circuits require continuous conduction
Temporary AV block terminates reentry

Indications

Paroxysmal Supraventricular Tachycardia
Diagnostic clarification of regular narrow-complex tachycardia
Pharmacologic stress testing (coronary vasodilation)

Dosing

Adult (IV rapid push):

Initial: 6 mg rapid IV bolus
If no response: 12 mg
May repeat 12 mg once

Administration:

Rapid push over 1–2 seconds
Immediately followed by saline flush
Continuous cardiac monitoring required

Contraindications

Absolute:

Second- or third-degree AV block (without pacemaker)
Sick sinus syndrome (without pacemaker)
Symptomatic bradycardia

Relative:

Severe asthma or active bronchospasm
Hypotension

Adverse Effects

Common (brief, self-limited):

Flushing
Chest pressure
Dyspnea
Lightheadedness
Transient asystole

Serious:

Bronchospasm
Prolonged heart block (rare)

Most side effects last < 30 seconds due to ultra-short half-life.

Drug Interactions

Antagonists:

Caffeine
Theophylline
Aminophylline

Potentiators:

Dipyridamole (inhibits adenosine uptake)

Use caution in patients on AV nodal blocking agents.

Monitoring

Continuous ECG monitoring
Blood pressure
Observe for transient AV block

Clinical Pearls

Extremely short half-life (~10 seconds)
Causes transient complete heart block
Diagnostic tool for differentiating SVT vs atrial flutter
Not effective for atrial fibrillation
Always give via large-bore IV with rapid flush
Warn patient: “You may feel strange for a few seconds.”

Comparison Within Antiarrhythmics

Compared to:

Adenosine:

Faster onset
Much shorter duration
Pure AV nodal effect
Diagnostic value