This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
GTN is given sub-lingually, why? 
Select and explain. 
A. To avoid first pass metabolism, B. Rapid effect, C. Gastric irritation, D. To avoid side effects
A: To avoid first pass metabolism
Answer: A: To avoid first pass metabolism 
Explanation: Ans: a (To avoid first pass metabolism) Ref: Goodman & Gilman, 11th ed, p. 3SUBLINGUAL ADMINISTRATIONVenous drainage from the mouth is to the superior vena cava, which protects highly soluble drugs like nitroglycerin from rapid hepatic first-pass metabolism. If a tablet of nitroglycerin were swallowed, the accompanying hepatic metabolism would be sufficient to prevent the appearance of any active nitroglycerin in the systemic circulation.