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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.

tmedweb.tulane.edu/pharmwiki/doku.php/bioavailability_the_first_pass_effect

Examples of Drugs with Significant First Pass Effect or Low Bioavailability Drug: Propranolol - ~26% Bioavailability because 75-85 % is metabolized by the liver before it can reach the circulation when taken orally.

www.sciencedirect.com/topics/medicine-and-dentistry/bioavailability

first-pass metabolism in the gut lumen, during passage across the gut wall or by the liver before the drug reaches the systemic circulation. The bioavailability of a drug has important therapeutic implications, because it is the major factor determining the drug dosage for different routes of administration.

ascpt.onlinelibrary.wiley.com/doi/abs/10.1002/cpt1977226888

The average bioavailability was found to be 18.4 ± 7.8% (SD, n = 5). It is shown that this low bioavailability depend almost entirely on the first‐pass metabolism of pentazocine following oral administration by application of intravenous clearance concepts.

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

3. bioavailability 4. 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

aibolita.com/.../45563-first-pass-metabolism-and-bioavailability.html

First-pass metabolism and bioavailability. Drugs may be destroyed by the acid in the stomach or by enzymes in the gastrointestinal tract, or may hardly be absorbed at all because of their chemical nature. These factors reduce the drug’s bioavailability.

pharmawiki.in/ppt-bioavailability-and-first-pass-metabolism

bioavailability 4. 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.

pubmed.ncbi.nlm.nih.gov/6362950

Bioavailability, defined as the ratio of the areas under the blood concentration-time curves, after extra- and intravascular drug administration (corrected for dosage if necessary), is often used as a measure of the extent of first-pass metabolism. When several sites of first-pass metabolism are in series, the bioavailability is the product of ...

pharmetrx.wordpress.com/2013/11/18/bioavailability-first-pass-metabolism

Bioavailability & First-pass metabolism. P. Chotsiri Pharmacokinetic 2013/11/18 2018/12/10 1 Minute. Bioavailability หรือที่ถูกนิยามให้เป็นภาษาไทย คือ ชีวปริมาณออกฤทธิ์ หรือ ชีวประสิทธิผล ...