PANRE Practice Test 13

A 54-year-old woman is brought to the emergency department after fainting twice at home. She takes methadone for opioid use disorder and started levofloxacin 3 days ago for community-acquired pneumonia. Between episodes, temperature is 37.4°C (99.3°F), heart rate 58/min, respirations 18/min, blood pressure 118/72 mmHg, and oxygen saturation 96% on room air, and ECG shows sinus bradycardia with a QTc of 610 ms. On the monitor she then has repeated, self-terminating runs of the rhythm shown: a polymorphic wide-complex tachycardia at about 240/min whose QRS amplitude waxes and wanes around the baseline. She remains awake with a palpable pulse. Electrolyte results are pending. Which of the following is the most appropriate pharmacotherapy?