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
Plasma drug monitoring is done for: 
Select and explain. 
A. Drug with high safety margin, B. Drug with low safety margin, C. Drug with high therapeutic index, D. None
B: Drug with low safety margin
Answer: B: Drug with low safety margin 
Explanation: None