Adenosine

Introduction to Adenosine

Adenosine is a crucial emergency medication in pediatric cardiology, primarily used for the acute treatment of paroxysmal supraventricular tachycardia (PSVT) in children.

Key Points:

Endogenous purine nucleoside
First-line treatment for PSVT in hemodynamically stable patients
Rapid onset and short duration of action
Can be used diagnostically to differentiate supraventricular from ventricular arrhythmias

Pharmacology of Adenosine

Adenosine acts primarily on the heart's electrical conduction system, specifically targeting the AV node.

Mechanism of Action:

Activates adenosine A1 receptors in the AV node
Slows AV nodal conduction
Can interrupt reentry circuits causing PSVT
Causes transient AV block

Pharmacokinetics:

Onset of action: Almost immediate (less than 10 seconds)
Duration of action: Very short (10-20 seconds)
Half-life: Less than 10 seconds
Metabolism: Rapidly taken up by erythrocytes and vascular endothelial cells

Clinical Applications in Pediatric Emergency Medicine

Adenosine's primary use is in the management of supraventricular tachycardia, but it has other applications in pediatric emergency care.

Indications:

Primary: Acute termination of PSVT
Secondary: Diagnostic tool for undifferentiated regular, narrow-complex tachycardias
May be used in wide-complex tachycardias of uncertain origin

Contraindications:

Second or third-degree AV block
Sick sinus syndrome
Known hypersensitivity to adenosine
Caution in patients with asthma or reactive airway disease

Dosing and Administration

Proper dosing and rapid administration are crucial for the effectiveness of adenosine.

Pediatric Dosing:

Initial dose: 0.1 mg/kg (maximum 6 mg)
Second dose: 0.2 mg/kg (maximum 12 mg) if needed
Subsequent doses: 0.3 mg/kg (maximum 12 mg) if required

Administration Technique:

Rapid IV push over 1-2 seconds
Administer into the largest and most proximal IV access
Follow immediately with a rapid saline flush
Elevate the extremity during administration

Note: Have resuscitation equipment readily available during administration.

Adverse Effects and Precautions

While generally safe, adenosine can cause significant, albeit transient, side effects.

Common Adverse Effects:

Flushing
Chest discomfort or pain
Dyspnea or feeling of suffocation
Headache
Transient arrhythmias during conversion

Rare but Serious Adverse Effects:

Bronchospasm (especially in patients with reactive airway disease)
Prolonged asystole
Atrial fibrillation

Precautions:

Use with caution in patients with asthma or reactive airway disease
Consider reduced dosing in patients taking dipyridamole or carbamazepine
May be less effective in patients taking methylxanthines (e.g., theophylline)
Continuous ECG monitoring is essential during administration