Adenosine

Adenosine

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Adenosine is an endogenous nucleoside that acts on specific A1 adenosine receptors. It depresses automaticity and conduction through the sinus and atrioventricular nodes and causes coronary vasodilatation. It has effects on supraventricular conduction but limited or no effect on ventricular conduction.

Adenosine is mainly used for the treatment of paroxysmal supraventricular tachycardias involving the atrioventricular (AV) node, and to help distinguish paroxysmal supraventricular tachycardia with aberrancy, from other broad complex tachycardias of ventricular origin.

Adenosine is rapidly removed from the circulation by the cytosolic enzymes of erythrocytes, endothelial cells and cardiomyocytes. This results in a very short half-life of less than ten seconds. Therefore, adenosine must be administered by rapid (over approximately 2 seconds) bolus injection into as large a vein as possible, followed immediately by a normal saline flush, so that as much of the drug as possible reaches the site of action before being metabolised. The very short duration of action means that repeat doses, other drugs, or electroconversion can be used soon after a dose of adenosine if needed.

Adverse effects are common but exceedingly short-lived (approximately 15 seconds). Prior to administration, patients should be warned that they might experience a short period of facial flushing, chest tightness, dizziness, dyspnoea and a sense of impending doom. Adenosine may cause bronchospasm in asthmatic patients. Adenosine has the advantage over verapamil in that it can be used in patients with poor left ventricular function or who are concurrently taking beta blockers, and in those who have broad complex tachycardias, which turn out to be ventricular tachycardias. Its disadvantage is a greater incidence of recurrence of paroxysmal supraventricular tachycardias after initial reversion, compared with verapamil. A number of medications, including carbamazepine, may exaggerate the AV node blockade associated with adenosine. In addition, dipyridamole (including the dipyridamole/aspirin combination product) may reduce the metabolism of adenosine, which also prolongs its duration of action.