Which drug is effective in terminating refractory paroxysmal supraventricular tachycardia (PSVT)?

Adenosine is the drug that is most effective in terminating refractory paroxysmal supraventricular tachycardia (PSVT). Adenosine works by temporarily blocking the conduction through the atrioventricular (AV) node, which can interrupt the reentrant circuits often responsible for PSVT. This action leads to a transient asystole that can restore normal sinus rhythm in patients who are experiencing this type of tachycardia.

In contrast, the other medications, while they may have some effect on heart rate and rhythm, are not the primary agents recommended for acute termination of PSVT. Verapamil, which is a calcium channel blocker, is effective in controlling rate in atrial fibrillation and may help with PSVT but is not as immediate or effective as adenosine in acutely terminating episodes. Digoxin, primarily used for heart failure and certain arrhythmias, typically does not provide rapid control in a tachycardia emergency. Amiodarone, while useful in a variety of arrhythmias, is generally reserved for more complex situations such as ventricular tachycardia or ventricular fibrillation, rather than acute management of PSVT.