A 45-yeаr-оld mаn hаd cоrоnary artery stents placed 2 days ago. Today, he is in severe distress and is reporting "crushing" chest discomfort. He is pale, diaphoretic, and cool to the touch. His radial pulse is very weak, blood pressure is 64/40 mm Hg, respiratory rate is 28 breaths per minute, and oxygen saturation is 89% on room air. When applied, the cardiac monitor initially showed ventricular tachycardia, which then quickly changed to ventricular fibrillationDespite a defibrillation attempt, the patient remains in ventricular fibrillation. Which drug and dose should you administer first to this patient?