Editing First pass effect (section)

== Hepatic first-pass ==
After a drug is swallowed, it is absorbed by the [[digestive system]] and enters the [[hepatic portal system]]. It is carried through the [[Hepatic portal vein|portal vein]] into the [[liver]] before it reaches the rest of the body. The liver [[metabolism|metabolizes]] many drugs, sometimes to such an extent that only a small amount of [[active pharmaceutical ingredient|active drug]] emerges from the liver to the rest of the [[circulatory system]]. This ''first pass'' through the liver thus may greatly reduce the [[bioavailability]] of the drug.

An example of a drug where first-pass metabolism is a complication and disadvantage is in the antiviral drug [[remdesivir]]. Remdesivir cannot be administered orally because the entire dose would be trapped in the liver with little achieving systemic circulation or reaching target organs and cells (for example, cells infected with [[SARS-CoV-2]]).<ref>{{Cite journal|doi = 10.1021/acsmedchemlett.0c00316|title = Advantages of the Parent Nucleoside GS-441524 over Remdesivir for Covid-19 Treatment|year = 2020|last1 = Yan|first1 = Victoria C.|last2 = Muller|first2 = Florian L.|journal = ACS Medicinal Chemistry Letters|volume = 11|issue = 7|pages = 1361–1366|pmid = 32665809|pmc = 7315846}}</ref><ref>{{cite web |title=Fact sheet for health care providers Emergency Use Authorization (EUA) of Veklury®(remdesivir) |website=[[Food and Drug Administration]] |url=https://www.fda.gov/media/137566/download |url-status=live |archive-url=https://web.archive.org/web/20200512234546/https://www.fda.gov/media/137566/download |archive-date=12 May 2020 |access-date=4 July 2024}}</ref> For this reason, remdesivir is administered by IV infusion, bypassing the portal vein. However, significant hepatic extraction still occurs because of second pass metabolism, whereby a fraction of venous blood travels through the hepatic portal vein and hepatocytes.