Editing First pass effect (section)

{{Short description|Phenomenon of drug metabolism}}
{{Distinguish|First dose effect}}
{{More citations needed|date=December 2016}}
[[File:2138 Hepatic Portal Vein System.jpg|thumb|Illustration showing the hepatic portal vein system]]
The '''first pass effect''' (also known as '''first-pass metabolism''' or '''presystemic metabolism''') is a phenomenon of [[drug metabolism]] at a specific location in the body which leads to a reduction in the [[concentration]] of the active [[drug]] before it reaches the site of action or systemic circulation.<ref name="Rowland1972">{{cite journal|last1=Rowland|first1=Malcolm|title=Influence of route of administration on drug availability|journal=Journal of Pharmaceutical Sciences|volume=61|issue=1|date=January 1972|pages=70–74|pmid=5019220|issn=0022-3549|doi=10.1002/jps.2600610111}}</ref><ref name="PondTozer1984">{{cite journal|last1=Pond|first1=Susan M.|last2=Tozer|first2=Thomas N.|title=First-Pass Elimination|journal=Clinical Pharmacokinetics|volume=9|issue=1|date=January 1984|pages=1–25|pmid=6362950|issn=0312-5963|doi=10.2165/00003088-198409010-00001|s2cid=28006040}}</ref> The effect is most associated with [[orally administered]] [[Medication|medications]], but some drugs still undergo first-pass metabolism even when delivered via an alternate route (e.g., [[Intravenous therapy|IV]], [[Intramuscular injection|IM]], etc.).<ref>{{Citation |last=Carlin |first=Michelle G. |title=Pharmacology and Mechanism of Action of Drugs |date=2023-01-01 |url=https://www.sciencedirect.com/science/article/pii/B9780128236772000866 |encyclopedia=Encyclopedia of Forensic Sciences, Third Edition (Third Edition) |pages=144–154 |editor-last=Houck |editor-first=Max M. |access-date=2024-01-17 |place=Oxford |publisher=Elsevier |doi=10.1016/b978-0-12-823677-2.00086-6 |isbn=978-0-12-823678-9|url-access=subscription }}</ref> During this metabolism, drug is lost during the process of [[Absorption (pharmacology)|absorption]] which is generally related to the [[liver]] and [[gut wall]]. The liver is the major site of first pass effect; however, it can also occur in the lungs, vasculature or other metabolically active tissues in the body. 

Notable drugs that experience a significant first pass effect are [[buprenorphine]], [[chlorpromazine]], [[cimetidine]], [[diazepam]], [[Alcohol (drug)|ethanol]] (drinking alcohol), [[imipramine]], [[Insulin (medication)|insulin]], [[lidocaine]], [[midazolam]], [[morphine]], [[pethidine]], [[propranolol]], and [[tetrahydrocannabinol]] (THC). 

First-pass metabolism is not to be confused with [[phase I metabolism]], which is a separate process.