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
Which of the following drugs have narrow therapeutic index 
Select and explain. 
A. Phenytoin, B. Lithium, C. Digoxin, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Therapeutic index measures the safety of the drug. Wider therapeutic index safer is the drug. Hence, drugs like lithium, Phenytoin, Digoxin which have narrow therapeutic index can become either ineffective or toxic with small variations in the dosage.