Adenosine

How it works

Acting on A1 receptors it transiently slows conduction through the atrioventricular node, interrupting re-entry circuits that depend on the AV node and restoring sinus rhythm.

Prescribing in practice

• It can cause transient asystole, profound bradycardia, and bronchospasm, so it must be given with continuous ECG and resuscitation facilities and used cautiously or avoided in asthma.
• Because its half-life is extremely short it must be given as a rapid bolus into a large proximal vein followed by an immediate saline flush.
• Effect is potentiated by dipyridamole and antagonised by caffeine and theophylline, and it should be avoided in second- or third-degree heart block without a pacemaker.

Monitoring

Record continuous ECG during administration to capture the rhythm response and to detect transient pauses, AV block, or new arrhythmia.

Counselling the patient

• Warn the patient they may briefly feel flushing, chest tightness, or a sense of impending doom that passes within seconds.
• Reassure that these effects are short-lived because the drug is broken down very quickly.
• Explain the heart rhythm is being recorded throughout to guide treatment.

Evidence & guidelines

Adenosine is the first-line agent for terminating AV-nodal-dependent supraventricular tachycardia in UK and Resuscitation Council tachycardia algorithms.