A patient, 3 days after an anterior wall MI, is in the critical care unit. She is currently receiving oxygen at 4 L/min by nasal cannula; nitroglycerin paste, 1 inch qh; and the beta-blocker Lopressor 25 mg PO qh. The monitor shows that she begins to have PVCs. Over the course of the next several hours, the PVCs increase in frequency to more than 15 per minute, with occasional runs of multifocal bigeminal PVCs. The patient's vital signs are heart rate, 84 beats/min, sinus rhythm, with described PVCs; blood pressure, 124/68 mm Hg; respirations, 20 breaths/min; SpO2, 92 Laboratory values are blood pH, 7.44; potassium, 4.4 mEq/L; and magnesium, 0.2 mEq/L. Which of the following, if ordered, would be inappropriate for this patient.