This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Electrolyte Imbalance, Subject name: Medicine
Immediate treatment for hyperkalemia with significant ECG changes? 
Select and explain. 
A. Calcium chloride, B. Calcium hydroxide, C. K+ Binding Resin Enema, D. Calcium Carbonate
A: Calcium chloride
Answer: A: Calcium chloride 
Explanation: Calcium increases threshold potential- restoring normal gradient between threshold potential and resting membrane potential (elevated abnormally in hyperkalemia) Calcium chloride - onset of action is < 5min and lasts about 30-60 min. Doses should be titrated with constant monitoring of ECG changes during administration Potassium binding resin exchanges Na+ for K+ :onset of action after PO ranges from 2-12 h. Calcium hydroxide and calcium carbonate have no role in management of hyperkalemia.