Question

Where does first pass metabolism occur? / what route of administration is used to avoid complete first pass metabolism?

Answer 1

First pass metabolism of a drug is said to occur when the concentration of a drug that is administered orally is significantly reduced before it reaches the systemic circulation. 
First pass metabolism usually occur in the liver.
The routes of drug administration that avoid complete first pass metabolism are: sublingual, transdermal, rectal and inhalation.