Adenosine

# Adenosine ## Overview - **Classification**: Antiarrhythmic (Class V, miscellaneous) - **Mechanism**: Activates A1 receptors in the AV node, leading to transient AV block and interruption of re-entry pathways. Ultra-short half-life of less than 10 seconds. ## Primary Indications 1. **Supraventricular Tachycardia (SVT)** - Conversion of paroxysmal SVT, including that associated with Wolff-Parkinson-White syndrome, to sinus rhythm. 2. **Diagnostic Aid** - To distinguish wide-complex tachycardias (SVT with aberrancy vs. ventricular tachycardia) when rhythm is stable and organized. 3. **Pharmacologic Stress Agent** - For myocardial perfusion imaging (e.g., cardiac stress test). ## Adult Dosing ### Standard Dosing **Paroxysmal Supraventricular Tachycardia (PSVT)** - **Dose**: Initial: **6 mg** - **Frequency**: Give as rapid IV bolus over 1-2 seconds. If no conversion after 1-2 minutes, administer **12 mg**. May repeat **12 mg** once after 1-2 minutes if needed. - **Route**: Rapid IV push via closest port to patient, followed immediately by rapid saline flush (5-10 mL). - **Maximum Dose**: **12 mg** per single dose. **Pharmacologic Stress Testing** - **Dose**: **0.14 mg/kg/min** - **Frequency**: Continuous IV infusion for 6 minutes. - **Route**: IV infusion. - **Total Dose**: Approximately **0.84 mg/kg**. ### Dose Adjustments - **Renal Impairment**: No adjustment needed due to rapid metabolism by adenosine deaminase. - **Hepatic Impairment**: No adjustment needed due to rapid metabolism by adenosine deaminase. - **Elderly Patients**: No specific adjustment needed; use standard adult dosing. May be more sensitive if comorbidities exist. ## Pediatric Dosing ### Neonates (0-28 days) - **Indication**: PSVT - **Dose**: Initial: **0.05 mg/kg** - **Frequency**: Rapid IV bolus. If no conversion, increase by **0.05 mg/kg** increments every 1-2 minutes. - **Maximum**: Single dose max **0.25 mg/kg** or **6 mg**, whichever is less. - **Special Notes**: Administer via rapid IV push followed by saline flush. ### Infants (1-12 months) - **Indication**: PSVT - **Dose**: Initial: **0.1 mg/kg** - **Frequency**: Rapid IV bolus. If no conversion, increase by **0.05 mg/kg** increments every 1-2 minutes. - **Maximum**: Single dose max **0.3 mg/kg** or **12 mg**, whichever is less. ### Children (1-12 years) - **Indication**: PSVT - **Dose**: Initial: **0.1 mg/kg** - **Frequency**: Rapid IV bolus. If no conversion, increase by **0.05 mg/kg** increments every 1-2 minutes. - **Maximum**: Single dose max **0.3 mg/kg** or **12 mg**, whichever is less. ### Adolescents (13-18 years) - **Indication**: PSVT - **Dose**: Follow adult dosing recommendations. Initial: **6 mg**. If no conversion, **12 mg**. - **Maximum**: Single dose max **12 mg**. ## Safety Information ### Contraindications - **Absolute**: - Second or third-degree AV block (unless a functioning artificial pacemaker is present). - Sick sinus syndrome (unless a functioning artificial pacemaker is present). - Known hypersensitivity to adenosine. - **Relative**: - Bronchoconstrictive or bronchospastic lung disease (e.g., asthma, COPD) due to risk of severe bronchospasm. - Heart transplant recipients (may be exquisitely sensitive, consider lower initial dose of **3 mg**). - Patients on dipyridamole or carbamazepine (may potentiate effects). ### Common Adverse Effects - **Very Common (>10%)**: Facial flushing, dyspnea/shortness of breath, chest discomfort/pressure, headache, lightheadedness/dizziness, nausea. - **Common (1-10%)**: Transient arrhythmias (bradycardia, AV block, asystole, PVCs), metallic taste, anxiety. - **Serious but Rare**: Sustained ventricular tachycardia/fibrillation (very rare), bronchospasm, myocardial infarction (extremely rare). ### Key Drug Interactions - **Dipyridamole**: Potentiates adenosine's effects. May require significant dose reduction (e.g., **3 mg** initial dose). - **Carbamazepine**: May enhance the AV-blocking effects of adenosine. - **Methylxanthines (Theophylline, Caffeine)**: Antagonize adenosine. Higher adenosine doses may be needed. - **Digoxin/Verapamil**: Additive depressant effects on the AV node; increased risk of AV block. ## Monitoring & Follow-up - **Before Treatment**: Ensure clear IV access, continuous ECG monitoring. - **During Treatment**: - Continuous cardiac monitoring (ECG) for rhythm and rate changes. - Blood pressure monitoring. - Respiratory status. - **Clinical Signs**: Expect a brief period of asystole (2-15 seconds) or severe bradycardia post-administration. Patient may report transient chest discomfort, flushing, dyspnea. ## Clinical Pearls - 💡 **Administration**: Always administer as a rapid IV bolus (1-2 seconds) followed immediately by a rapid 5-10 mL saline flush to ensure delivery into central circulation before degradation. - 💡 **Site Selection**: Administer into the largest, most proximal vein possible (e.g., antecubital or jugular) to facilitate rapid delivery to the heart. - 💡 **Patient Counseling**: Warn patients about the expected transient discomforts (flushing, chest pressure, sensation of breathlessness) that typically last only seconds. - 💡 **Half-life**: Its extremely short half-life makes it ideal for diagnosis and treatment of PSVT, as adverse effects are usually brief. > **⚠️ Important**: This information is for educational purposes only. Always consult current prescribing information, local guidelines, and clinical judgment before prescribing.