A 52-year-old man presents to the emergency room with nausea, vomiting, muscle cramps, and weakness that began three days ago. He recently started Penicillin G for pharyngitis and is also taking lisinopril, atorvastatin, and spironolactone. On examination, he appears anxious, has difficulty walking, and exhibits decreased sensations and reflexes. Laboratory studies reveal a potassium level of 6.8 mmol/L, and his ECG shows changes consistent with hyperkalemia. Which of the following is the antidote of choice for life-threatening arrhythmias caused by hyperkalemia?
