Mechanism of action

Adenosine works by slowing down the impulse transmission through the atrioventricular (AV) node, thereby interfering with the pathway that enables reentry tachyarrhythmias (AVNRT and AVRT). These arrhythmias rely on AV node transmission. By disrupting this transmission, the reentry- and hence, the arrhythmia- may be terminated. Generally, adenosine is considered safe for patients with narrow complex tachycardia (NCT).

Adenosine typically causes a short-lasting second- or third-degree AV block which may be unpleasant to the patient. This side effect lasts a few seconds. Case reports have indicated that the risk of high-degree AV block and ventricular arrhythmias is greater in patients on digoxin or verapamil, although this is not an established drug interaction.

The half-life of adenosine is 8 seconds. Adverse effects are therefore very brief.

Indications

Paroxysmal supraventricular tachycardia (PSVT), which includes forms that are caused by pre-excitation.
Myocardial perfusion scintigraphy.

Contraindications

Asthma and COPD. Adenosine has caused mild to moderate exacerbation of asthma symptoms. Adenosine should be used with caution in patients with obstructive lung disease or asthma.
Irregular wide complex tachycardia (absolute contraindication).

Irregular wide complex tachycardia is most often due to atrial fibrillation with wide QRS complexes due to bundle branch blocks or other conduction defects. However, in rare instances, it may be due to *pre-excited atrial fibrillation (i.e.* atrial fibrillation with impulses conducted via an accessory pathway [see Wolff-Parkinson-White Syndrome]); blocking AV node conduction may result in accelerated transmission of atrial impulses to the ventricles and thus ventricular fibrillation and cardiac arrest.

High-degree AV block (second-degree Mobitz type 2 AV block, third-degree AV block).
Sick sinus syndrome or symptomatic bradycardia in the absence of a pacemaker.
Hypersensitivity to adenosine.

Administration

Normal route: Peripheral intravenous (IV).
Alternative route: Central venous administration of adenosine is suitable in the intensive care unit or coronary care unit.
Adenosine injection must be administered quickly (1-2 seconds), followed immediately by a rapid saline flush (use a three-way tap system).
Compatible IV fluids: normal saline.
Storage: room temperature.

Dosage

Adults

Initial dose: 6 mg
Wait 60 seconds before attempting a second dose.
Second dose: 12 mg.
Wait 60 seconds before attempting a third dose.
Third dose: 12 or 16 mg.

Renal failure or renal replacement therapy

No dosage adjustment is required in renal failure or renal replacement therapy.

Pediatric patients

Body weight < 50 kg:

Initial dose: 0.05 to 0.1 mg/kg

Second dose: Increase the dose by 0.05 to 0.1 mg/kg.
Maximum single dose: 0.3 mg/kg

Body weight >50 kg:

Adult dosage.

Adverse effects

Adverse effects typically persist <10 seconds due to the short half-life of adenosine.

Anxiety
Chestpain.
Palpitations.
Headache
Hypotension.
Facial flushing.
Sweating.
Bronchospasm
Dyspnea
Nausea
Metallic taste
Tightness in throat
Lightheadedness, dizziness, tingling in arms, numbness, blurred vision, burning sensation.

Relevant reading

https://ecgwaves.com/topic/diagnosis-management-tachycardia-tachyarrhythmia-wide-narrow/

References

Drug Bank

Zipes et al: Arrhythmology, Elsevier (2019).

Wellington ICU Drug Manual

Adenosine for tachyarrhythmias (AVNRT, AVRT, NCT)