2-year-old boy was brought to the emergency department because of fever, irritability, increased lethargy, and multiple episodes of diarrhea. The mother reported that she found her levothyroxine bottle empty a few hours earlier. Vital signs of the boy were blood pressure 130/80 mm Hg, heart rate 180 bpm, respirations 26/min. Laboratory test results on admission showed a total tri-iodothyronine level of 472 ng/dL (normal:
40-130 ng/dL). Which of the following drugs should be administered first to control hormone-related effects that could be rapidly lethal in this patient?