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Adenosine 💊

⚡ Patients often feel an intense, unpleasant sensation for 20–30 seconds after adenosine - this is always transient. ✅ Reassure them it will quickly pass. 🚫 Do not use in asthmatics (risk of severe bronchospasm).

📖 About

Purine nucleotide used to treat supraventricular tachycardias (SVTs).
Adenosine receptor agonist (mainly A1 receptors in the heart).
Always check the BNF link here.

⚙️ Mode of Action

Activates A1 purinergic receptors at the SAN and AVN.
Inhibits adenylate cyclase → ↓cAMP → increased outward K⁺ flux.
Causes hyperpolarisation of nodal tissue → slows AV nodal conduction.

🫀 Actions

Produces transient AV block, bradycardia, or even brief asystole.
Does not cardiovert AF or flutter, but may transiently slow AV conduction and unmask flutter waves.
Also acts as a vasodilator → flushing, hypotension.
Very short half-life (<10 seconds) → must reach the AV node before metabolism.

💉 Dose & Administration – Adenosine (verify with BNF/datasheet)

Indication / Context	Details
⚡ Sensitised patients (on dipyridamole, carbamazepine, post-transplant, or via central line)	Adenosine • Dose: 1–3 mg stat • Route: Rapid IV bolus into large vein • Flush: Immediately with 20 mL 0.9% NaCl
➡️ Standard first dose	Adenosine • Dose: 6 mg stat • Route: Rapid IV bolus + 20 mL NS flush • Note: If ineffective, escalate
🔁 If 6 mg ineffective	Adenosine • Dose: 12 mg stat (may repeat once) • Route: Rapid IV bolus + 20 mL NS flush
💡 Administration Notes	• Give via large peripheral or central vein • Follow immediately with 20 mL NS flush • Warn patient of transient unpleasant effects (flushing, chest pressure, breathlessness, sense of doom)

🩺 Indications

Termination of paroxysmal SVTs (AVNRT, AVRT).
Diagnostic aid: can unmask atrial flutter/fibrillation waves.
Used in myocardial perfusion imaging (diagnostic pharmacology).

🚫 Contraindications

Asthma or severe COPD (risk of bronchospasm) → consider verapamil instead.
Long QT syndrome, sick sinus syndrome, 2nd/3rd-degree AV block (unless paced).
Heart transplant patients: extremely sensitive (use lower dose).

⚠️ Side Effects

Transient: chest discomfort, flushing, dyspnoea, nausea, sense of impending doom.
Bradyarrhythmia, sinus pause, complete heart block (short-lived).
Bronchospasm in susceptible patients.

🔄 Interactions

Dipyridamole: potentiates effect → use reduced starting dose (as low as 1 mg).
Theophylline/aminophylline: antagonise adenosine → reduced effect.
Carbamazepine: enhances AV block → use lower doses.

📚 References

BNF: Adenosine

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