This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
The initial pharmacologic therapy of choice in this stable patient (refer to Q 87) is 
Select and explain. 
A. Adenosine 6 mg rapid IV bolus, B. Verapamil 2.5 to 5 mg IV over 1 to 2 min, C. Diltiazem 0.25 mg /kg IV over 2 min, D. Digoxin 0.5 mg IV slowly
A: Adenosine 6 mg rapid IV bolus
Answer: A: Adenosine 6 mg rapid IV bolus 
Explanation: Vagotonic maneuvers such as carotid massage or the Valsalva maneuver could ceainly be tried first. If these are unsuccessful, adenosine, with its excellent safety profile and extremely sho half-life, is the drug of choice for supraventricular tachycardia at an initial dose of 6 mg. Dosage can be repeated if necessary a few minutes later at 12 mg. Verapamil is the next alternative; if the initial dose of 2.5 to 5 mg does not yield conversion, one or two additional boluses 10 min apa can be used. Diltiazem and digoxin may be useful in rate control and conversion, but have a much slower onset of action.