A 58-year-old woman presented to the Emergency Department with a large fluctuant swelling the site of a recent insect bite. She is anxious, tachycardic and pyrexial. An ECG shows critical fibrillation. She is noted to have a goiter. The swelling at the site of the bite requires surgical drainage. Which of the following classes of drug would be most appropriate as part of her preoperative preparation for surgery?