How is adenosine pharmacologically classified?

• A. Beta blocker
• B. Vasodilator
• C. Antiarrhythmic
• D. Calcium channel blocker

Answer: (C)

Adenosine is best thought of as an antiarrhythmic agent. It terminates certain fast heart rhythms—specifically paroxysmal supraventricular tachycardia—by causing a brief block in conduction through the AV node. This happens because adenosine binds to A1 receptors in the AV node, which opens potassium channels, hyperpolarizes the cell, and reduces calcium influx. The result is a transient slowdown or interruption of AV nodal conduction, which can interrupt reentrant circuits that drive the tachycardia.

Its effects are extremely short-lived, because adenosine has a very rapid half-life. Clinically, it’s given as a rapid IV push followed by a saline flush so the drug reaches the heart quickly before it is cleared. You’ll typically see a rapid onset of effect, sometimes a brief pause in rhythm, and then restoration of a normal rhythm if the tachycardia terminates.

It’s not a beta blocker, not a vasodilator, and not a calcium channel blocker. Those classes work through different receptor targets or ion-channel mechanisms, whereas adenosine’s action is through purinergic receptors leading to a temporary AV nodal block. Use is acute (for terminating SVT) rather than for long-term rhythm control, and there are cautions like potential bronchospasm and avoidance in certain AV conduction disorders.