What is the maximum dose for the first adenosine administration in the stable narrow complex tachycardia protocol?

• A. 3 mg
• B. 9 mg
• C. 6 mg
• D. 12 mg

Answer: (C)

Adenosine is used in stable narrow complex tachycardia to transiently block AV nodal conduction and interrupt AV-nodal dependent reentrant circuits, delivering rapid, short-lived effects that help reveal or terminate the rhythm. Because it acts very quickly and has a short half-life, dosing starts low and is given as a rapid IV push with a saline flush to ensure it reaches the heart promptly. The standard starting dose is 6 mg, and this is the maximum for the first administration. If there’s no response after a short interval, a second dose of 12 mg can be given, and sometimes a third 12 mg dose may be used, but the initial dose remains 6 mg to balance effectiveness with safety.