Adenosine (Adenocard, Adenoscan)

Transient Asystole - Expected and brief (6-12 sec); warn the awake patient beforehand; have atropine and pacing immediately available.

Preprocedural Counseling Reduces Anxiety - Patients commonly experience an intense sense of doom, chest tightness, and dyspnea - brief counseling prior to pushing this drug will help reduce anxiety.

Bronchospasm Risk - Avoid or use with extreme caution in reactive airway disease, asthma, or COPD; adenosine receptor activation causes bronchoconstriction.

Drug Interactions (Potentiation) - Dipyridamole blocks adenosine uptake, markedly potentiating and prolonging its effect; reduce dose significantly or avoid. Carbamazepine may potentiate AV block.

Drug Interactions (Antagonism) - Methylxanthines (caffeine, theophylline, aminophylline) competitively antagonize adenosine receptors; higher doses may be required or drug may be ineffective.

Administration Technique - Must be given as a rapid IV bolus (1-2 sec) via a large peripheral or central vein, immediately followed by a 20 mL saline flush; slow administration renders drug ineffective due to rapid metabolism.

Dosing Escalation - If initial 6 mg dose is ineffective after 1-2 min, repeat with 12 mg; may repeat 12 mg once more if needed.

Cardiac Transplant - Denervated hearts are exquisitely sensitive; start at 3 mg and titrate cautiously.

Wolff-Parkinson-White (WPW) - Effective for terminating AV reentrant tachycardia, but may precipitate AF with rapid conduction down the accessory pathway; use with caution; synchronized cardioversion preferred if WPW with AF suspected.

Management of Excessive Effect - Asystole or prolonged heart block is self-limiting given ultra-short half-life (~10 sec); supportive care (atropine, transcutaneous pacing) if prolonged; aminophylline (50-100 mg IV) can antagonize effect.

Pediatric Implications: Dosing is weight-based (0.1 mg/kg initial, max 6 mg; 0.2 mg/kg repeat, max 12 mg). Same rapid bolus technique required. Generally well tolerated; similar side effect profile.

Obstetric Implications: Limited data; case reports support use for maternal SVT in pregnancy. Rapid metabolism limits fetal exposure. Not expected to cause significant fetal effects at standard doses. May be used when benefits outweigh risks; consider continuous fetal monitoring.

Absolute:

Second- or third-degree AV block (without functioning pacemaker)

Sick sinus syndrome (without functioning pacemaker)

Known hypersensitivity to adenosine

Relative:

Asthma or reactive airway disease

WPW with atrial fibrillation or flutter

Pre-excited atrial arrhythmias

Caution:

Cardiac transplant recipients (use reduced dose)

Patients on dipyridamole or carbamazepine

Patients consuming methylxanthines (may require higher doses or be ineffective)

Long QT syndrome

6 mg rapid IV push (initial); 12 mg if no response after 1-2 min (may repeat 12 mg once)

Pediatric (weight-based): 0.1 mg/kg initial (max 6 mg); 0.2 mg/kg repeat (max 12 mg)

Pharmacologic stress testing (Adenoscan): 140 mcg/kg/min over 6 min via continuous infusion

Pharmacologic stress testing (Adenoscan): 140 mcg/kg/min over 6 min

Activates cardiac A1 adenosine receptors -> increases K+ conductance and inhibits cAMP -> hyperpolarizes AV nodal cells -> slows and transiently blocks AV conduction, interrupting reentrant circuits. Also activates A2 receptors in coronary vasculature -> vasodilation.

Rapid intravascular and cellular uptake; deamination to inosine and phosphorylation to AMP by erythrocytes and vascular endothelium. Half-life <10 seconds.

Intravascular (not organ-dependent); eliminated as uric acid via renal excretion

Must be stored at room temperature; do not refrigerate (crystallization)

Adenocard (antiarrhythmic) and Adenoscan (stress testing) are different concentrations and infusion strategies - do not interchange

Adenoscan vials (3 mg/mL, 30 mL) vs. Adenocard vials (3 mg/mL, 2 mL or 4 mL)

Differential Diagnosis Use - Adenosine can unmask atrial flutter, fibrillation, or other atrial arrhythmias by transiently blocking AV conduction. This can aid in diagnosis.