This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CHF, Angina Pectoris and Myocardial Infarction, Subject name: Pharmacology
Which of the following is an active metabolite of another drug and is available as a separate drug for the treatment of angina? 
Select and explain. 
A. Isosorbide mononitrate, B. Isosorbide dinitrate, C. Nitroglycerine, D. Propanolol
A: Isosorbide mononitrate
Answer: A: Isosorbide mononitrate 
Explanation: Isosorbide mononitrate (IMN) is a metabolite of isosorbide dinitrate (IDN) and is also available as a separate drug. IMN undergoes min. first pass metabolism. Nitroglycerine: High first pass metabolism.