====== Adenosine (Adenocard®, Adenoscan®) ======

<WRAP right 300px>
<WRAP infobox>
^ Drug Overview |
| Class | [[cardio:arrhythmias:start|Antiarrhythmics]] |
| Subclass | Miscellaneous (AV Nodal Suppressant) |
| Primary Use | [[cardio:arrhythmias:psvt|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 |
</WRAP>
</WRAP>

===== 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.

<WRAP clear></WRAP>

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===== 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

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===== Indications =====

  * [[cardio:arrhythmias:psvt|Paroxysmal Supraventricular Tachycardia]]
  * Diagnostic clarification of regular narrow-complex tachycardia
  * Pharmacologic stress testing (coronary vasodilation)

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===== 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

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===== Contraindications =====

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

Relative:
  * Severe asthma or active bronchospasm
  * Hypotension

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===== 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.

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===== Drug Interactions =====

Antagonists:
  * Caffeine
  * Theophylline
  * Aminophylline

Potentiators:
  * Dipyridamole (inhibits adenosine uptake)

Use caution in patients on AV nodal blocking agents.

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===== Monitoring =====

  * Continuous ECG monitoring
  * Blood pressure
  * Observe for transient AV block

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===== 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.”

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===== Comparison Within Antiarrhythmics =====

Compared to:
  * [[cardio:beta_blockers:start|Beta-Blockers]]
  * [[cardio:ccb:non_dhp|Non-DHP Calcium Channel Blockers]]

Adenosine:
  * Faster onset
  * Much shorter duration
  * Pure AV nodal effect
  * Diagnostic value

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===== Related =====

  * [[cardio:arrhythmias:start|Dysrhythmias Module]]
  * [[cardio:arrhythmias:psvt|PSVT]]
  * [[cardio:arrhythmias:dofetilide|Dofetilide]]
  * [[cardio:arrhythmias:amiodarone|Amiodarone]]