adenosine
antiarrhythmic· Brands: Adenocard, AdenoscanIV
Mechanism of action
Adenosine is an endogenous purine nucleoside that acts on A1 adenosine receptors in the heart. It causes transient atrioventricular (AV) nodal block by increasing potassium conductance and reducing cyclic AMP, slowing conduction through the AV node. This interrupts re-entrant circuits that include the AV node, terminating paroxysmal supraventricular tachycardias. It also causes coronary vasodilation.
Pharmacokinetics
Adenosine is taken up by cells and rapidly metabolised by adenosine deaminase, with a plasma half-life of less than 10 seconds. Its effects are therefore brief. It is administered as a rapid intravenous bolus. Metabolism occurs in the endothelium and red blood cells, with no significant hepatic or renal elimination. The onset of action is immediate, and the duration of effect is typically 10 to 30 seconds.
Indications & dosing
Paroxysmal supraventricular tachycardia (PSVT) termination
Initial 6 mg rapid IV push; if no conversion after 1-2 min, give 12 mg, may repeat 12 mg once.
- adult · IV: 6 mg Rapid IV push · Initial 6 mg rapid IV push; if no conversion after 1-2 min, give 12 mg, may repeat 12 mg once.
Pharmacologic stress testing (myocardial perfusion imaging)
Infuse at 140 mcg/kg/min for 6 minutes; monitor for adverse effects such as flushing, chest pain, arrhythmias.
- adult · IV: 140 mcg/kg/min Continuous infusion · Infuse at 140 mcg/kg/min for 6 minutes; monitor for adverse effects such as flushing, chest pain, arrhythmias.
Paroxysmal supraventricular tachycardia (PSVT) termination (pediatric)
Initial 0.1 mg/kg (max 6 mg); if no response, give 0.2 mg/kg (max 12 mg) after 1-2 min.
- pediatric · IV: 0.1–0.2 mg/kg Rapid IV push · Initial 0.1 mg/kg (max 6 mg); if no response, give 0.2 mg/kg (max 12 mg) after 1-2 min.
Contraindications & precautions
- Second- or third-degree AV block without a functioning pacemaker · Adenosine can further depress AV conduction and cause complete heart block.
- Sick sinus syndrome without a functioning pacemaker · Adenosine can exacerbate bradyarrhythmias and cause prolonged asystole.
- Asthma or severe bronchospastic disease · Adenosine can induce bronchoconstriction and precipitate severe respiratory distress.
- Known hypersensitivity to adenosine · Includes allergy to adenosine or any formulation component.
- Transplanted heart · Patients with a cardiac transplant are hypersensitive to adenosine, risking prolonged asystole.
- Administer as a rapid IV push (over 1-2 seconds) with a saline flush to ensure delivery to the heart.
- Monitor ECG continuously during administration and have resuscitation equipment available.
- Reduce the dose in patients taking dipyridamole (which potentiates adenosine).
- Consider a higher dose in patients taking methylxanthines (e.g., theophylline, caffeine) that antagonise adenosine.
- Use caution in patients with a history of bronchospastic disease or severe asthma, and in coronary artery disease (risk of angina).
- Avoid in patients with a transplanted heart due to the risk of prolonged asystole.
Adverse effects
- Flushing of the face, neck, and upper chest
- Dyspnoea or a sense of chest tightness
- Chest pain (typically transient)
- Nausea and headache
- Hypotension (usually transient)
- Bradycardia (may progress to asystole)serious
- Asystole (brief, usually self-limiting, but requires emergency management)serious
- Bronchospasm in at-risk patientsserious
Monitoring, pregnancy & toxicity
- Continuous ECG and heart rate monitoring · During administration
- Blood pressure · During and after administration
- Respiratory status, especially in patients with asthma or COPD · During and after administration
- Pregnancy: Use in pregnancy only if clearly needed. Limited human data, but the short half-life and rapid metabolism minimise fetal exposure.
- Toxicity: Profound bradycardia or transient asystole · Transient and usually resolves without intervention. Monitor and provide supportive care. Atropine may be given if prolonged.
- Toxicity: Hypotension · Transient. Supportive measures with fluids if needed.
- Toxicity: Bronchospasm · In patients with asthma or COPD, may precipitate bronchospasm. Treat with inhaled beta-agonists if necessary.
- Toxicity: Chest pain and flushing · Common and transient. Reassure the patient.
Clinical notes
Adenosine is used to terminate paroxysmal supraventricular tachycardia (PSVT) when vagal manoeuvres have failed. It is given as a rapid intravenous bolus, preferably into a large vein with a saline flush. Typical adult doses are 6 mg followed by 12 mg after 1 to 2 minutes if conversion has not occurred, then a further 12 mg if needed. Transient adverse effects include flushing, chest tightness, dyspnoea, and a feeling of impending doom; these are usually short-lived. Adenosine is contraindicated in second- or third-degree AV block, sick sinus syndrome, asthma, and in patients taking dipyridamole. Caution is needed in those with a transplanted heart, as they may be extremely sensitive to the effects of adenosine.
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BNF; local formulary