The initial pharmacologic therapy of choice in this stable patient (refer to Q 87) is
Adenosine 6 mg rapid IV bolus
Verapamil 2.5 to 5 mg IV over 1 to 2 min
Diltiazem 0.25 mg /kg IV over 2 min
Digoxin 0.5 mg IV slowly
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.