This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
An old man enters the hospital with myocardial infarction and a severe ventricular arrhythmia. The antiarrhythmic drug chosen has a narrow therapeutic window. The minimum toxic plasma concentration is 1.5 times the minimum therapeutic plasma concentration. The half life is 6 hrs. It is essential to maintain the plasma concentration above the minimum therapeutic level to prevent a possible lethal arrhythmia. Of the following, the most appropriate dosing regimen would be 
Select and explain. 
A. Once a day, B. Twice a day, C. Four times a day, D. Constant intravenous infusion
D: Constant intravenous infusion
Answer: D: Constant intravenous infusion 
Explanation: None