Question

Explain the principle of First Pass metabolism and the importance of consideration of this process when giving an oral medication?

Answer 1

In first pass metabolism the drug enters the liver first which is the prime site of first pass metabolism and after that it goes to portal vein and then the circulatory system. The bioavailability of drug is reduced because it has to go through the liver and get affected by hepatic enzyme and gut enzymes. A fraction of drug is lost in this process. Many drugs like cannabis have enhanced effect with this process also . The parenteral route bypasses this so drugs may have different doses compared to oral and iv. In liver disorders same drug can become toxic as more biovailability is there . Two drugs given together competing for bioavailability also effect the sustemic concentration of the drug