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en.wikipedia.org/wiki/First_pass_effect

The first pass effect (also known as first-pass metabolism or presystemic metabolism) is a phenomenon of drug metabolism whereby the concentration of a drug, specifically when administered orally, is greatly reduced before it reaches the systemic circulation. It is the fraction of drug lost during the process of absorption which is generally related to the liver and gut wall.

www.labce.com/spg1094059_first_pass_hepatic_metabolism.aspx

First Pass Hepatic Metabolism Phase I metabolic reactions can occur during the absorptive phase in the gut wall or liver before reaching the blood stream. This results in a reduction in the concentration of the drug before it reaches the circulation.

www.sciencedirect.com/.../first-pass-effect

A first-pass effect is defined as a low systemic availability of the drug as a result of significant metabolism. Although a first-pass effect can occur in a variety of tissues, including the intestines Doherty and Pang (1997) and uterus De Ziegler et al (1997), it is most often observed with the liver. Drug absorbed from the gastrointestinal tract travels immediately to the liver through the ...

www.ncbi.nlm.nih.gov/pubmed/6362950

Clinically, first-pass metabolism is important when the fraction of the dose administered that escapes metabolism is small and variable. The liver is usually assumed to be the major site of first-pass metabolism of a drug administered orally, but other potential sites are the gastrointestinal tract, blood, vascular endothelium, lungs, and the ...

www.researchgate.net/post/What_are_the_drugs_that_do_not_undergo_first-pass...

First-pass effect consists of (a) intestinal first pass effect-and (b) hepatic first-pass effect. a. Intestinal first-pass effect : Drugs may be metabolized by gastric acid, digestive enzymes or ...

medical-dictionary.thefreedictionary.com/first-pass+metabolism

first-pass metabolism the intestinal and hepatic degradation or alteration of a drug or substance taken by mouth, after absorption, removing some of the active substance from the blood before it enters the general circulation. Synonym(s): first-pass effect first-pass me·tab·o·lism , first-pass effect (fĭrst-pas mĕ-tab'ŏ-lizm, e-fekt') The ...

sepia.unil.ch/pharmacology/index.php?id=55

Hepatic first pass effect: All drug dose absorbed from the gastrointestinal tract is first delivered to the liver by the portal vein. A fraction of the drug can then be metabolized in the liver before it even reaches the systemic circulation. Therefore the oral bioavailability of the drug is reduced.

study.com/academy/lesson/the-first-pass-effect-in-pharmacology.html

The First Pass Effect. When you take a medication by mouth, it doesn't just magically get into your body and start doing its thing. It actually has to go through a whole host of organs and a big ...

pharmawiki.in/.../uploads/2014/01/Bioavailability-And-First-Pass-Metabolism.pdf

first pass metabolism 5. primary systems effect presystemic metabolism 6. hepatic enzymes 7. drug interactions involving drug metabolism 8. evidences of first pass effect 9. liver extraction ratio 10. relationship between absolute bioavailability and liver extraction 11. estimation of reduceds bioavailability due to liver

www.ncbi.nlm.nih.gov/books/NBK551679

The first pass effect is a phenomenon in which a drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug upon reaching its site of action or the systemic circulation. The first pass effect is often associated with the liver, as this is a major site of drug metabolism. However, the first pass effect can also occur in the lungs ...