What is the initial pharmacologic dose of adenosine for terminating a stable AVNRT or AVRT?

• A. 12 mg IV bolus; if needed, 24 mg
• B. 6 mg IV bolus; if needed, 12 mg
• C. 3 mg IV bolus; if needed, 6 mg
• D. 1 mg IV bolus; if needed, 2 mg

Answer: (B)

Adenosine terminates AVNRT or AVRT by briefly blocking conduction through the AV node, interrupting the reentrant circuit. Because it is cleared extremely quickly (half-life of only a few seconds), it must be given as a rapid IV bolus (followed by a saline flush) to reach the AV node before it is cleared.

The standard starting dose in adults is 6 mg. If there is no termination within a few seconds, a second dose of 12 mg is given. This dosing approach balances effectiveness with safety, using a dose high enough to acutely block the AV node but not so large as to cause unnecessary side effects. Lower initial doses are typically insufficient to terminate the tachycardia, while a first-dose 12 mg is not necessary in most cases and increases the risk of adverse effects.